The University of Adelaide

School of Mechanical Engineering

Gas Turbine Reheat Combustor

Final Report

Project Number: 1830

Helen Hobbs (1211714)Fiona Lake (1160419)

Alexander Schumacher (1629503)

Supervisors:Dr Paul MedwellDr Cristian Birzer

Dr Zhao Tian

October 30, 2015

Word Count: 16,125

Abstract

Combustion is the leading method for the generation of electricity. Despite the development ofalternative energy sources, combustion technology will remain dominant in meeting the risingenergy demands for the foreseeable future. However, a paradox arises as a greater demandof energy is evolving alongside a growing recognition of environmental degradation as a resultglobal warming. The negative changes occurring in the environment can be correlated withpollutants, in particular those that are generated from the combustion process. Strict emissionregulations and an industry-wide focus on reducing operational cost has developed a drivingfocus on increasing the efficiency of combustion and reducing unwanted by-products. Moderateor Intense Low oxygen Dilution (MILD) is a unique combustion regime capable of meetingthese desired objectives. The framework of the regime is characterised by reactants at elevatedtemperatures and low oxygen concentrations. Together, these specifications work to create adistributed and more homogeneous reaction zone facilitating higher thermal efficiency and lowerthermal nitrogen oxides and soot production. As such, it can be advantageous to any combustionapplication where MILD is a feasible alternative.

The application of MILD combustion has been successfully applied in furnace environments,and shows promise in gas turbine applications. However, the absence of a sound fundamentalknowledge-base limits confidence regarding function. The scope of this continuation project is toestablish a MILD reaction in a linear, sequential combustion apparatus enabling the collection ofclear, experimentally repeatable data. The apparatus rig enables the varying of input parametersto generate a detailed understanding of flame stability and determine extinction points duringexperimental testing. This subsequent testing will be used to validate redesigned componentsby establishing MILD combustion, and further fundamental knowledge on the stability of MILDflame in an apparatus representative of practical systems.

This document demonstrates the research undertaken and the process pertaining to the redesignof the apparatus components fundamental to the evolution of a MILD flame. The necessary eval-uation of an existing design is presented, from which updated concept designs were based. Fromthe installation of these components, an experimental testing program was launched focusingon three areas, an iterative burner assessment, parametric coflow study and a visual assessmentof jet flames. Via this study, an improved auxiliary burner system was developed, redesignedcomponents were validated and MILD combustion was established using natural gas. Subse-quent qualitative and quantitative flame analysis was completed using standard photographsand OH* chemiluminescence images. Through the use of these tools and data processing soft-ware, conclusions were realised pertaining to the stability of the jet flames. These conclusions,in addition to preliminary pressurisation design work, will be significant for future research andin the broadening of MILD combustion knowledge.

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Acknowledgements

As a group we would like to thank Dr Paul Medwell and Dr Cristian Birzer for their supportand guidance throughout the project. Marc Simpson for teaching us patience. Pascale Symonsfor his countless hours cutting plates, producing ring burners and helping in the job crisis.

Special thanks also go to:

• The School of Mechanical Engineering workshop; for their general guidance and assistancein developing a feasible design

• The School of Mechanical Engineering for their continued assistance and support in com-pleting the project

• The Asian Office of Aerospace Research & Development

• The Air Force Research Laboratory

• The Australian Research Council

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Contents

1 Introduction 1

2 Background 32.1 Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Flame Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 Combustion products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3.1 Carbon Monoxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3.2 Hydroxyl Radical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.4 MILD Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.5 Gas Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 Prior Work 163.1 Cabra Vitiated Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.2 Adelaide Jet-in-hot coflow burner . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.3 Delft Jet-in-hot coflow burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.4 Jet-in-hot Crossflow burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.5 DLR JHC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4 Aims 234.1 Primary Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.1.1 Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.1.2 Experimental goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.2 Extension Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5 Combustor Design 265.1 Original Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265.2 Original Design Weaknesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285.3 Design Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5.3.1 Primary Jet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305.3.2 Auxiliary Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.3.3 Flow Conditioner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345.3.4 Extension Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

6 Experimental Testing 396.1 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.3 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

6.3.1 Combustor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.3.2 Gas Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.3.3 Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426.3.4 Measurement Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . 446.3.5 Cameras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.3.6 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6.4 Central Jet Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.4.1 Coflow Input Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.4.2 Central Jet Input Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 48

6.5 Coflow Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

7 Experimental Results and Analysis 497.1 Auxiliary burner testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497.2 Coflow Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

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7.2.1 Coflow Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507.2.2 Coflow Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527.2.3 Coflow species composition . . . . . . . . . . . . . . . . . . . . . . . . . . 55

7.3 Coflow Testing with Flow Conditioner . . . . . . . . . . . . . . . . . . . . . . . . 577.4 Central Jet Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

7.4.1 Key Flame Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 587.4.2 Jet Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607.4.3 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647.4.4 Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667.4.5 MILD combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

8 Design of Future Components 718.1 Preliminary Design of Pressurised Combustor . . . . . . . . . . . . . . . . . . . . 71

8.1.1 Design Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718.1.2 Design Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718.1.3 Final Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728.1.4 Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738.1.5 Design calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738.1.6 Future Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

8.2 Future Auxiliary Burner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748.3 Future Flow Conditioner Concept Designs . . . . . . . . . . . . . . . . . . . . . . 75

9 Conclusions 76

10 Future Work 79

Appendices 84

Appendix A Management 84A.1 Work Breakdown Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84A.2 Gantt Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87A.3 Project Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90A.4 Risk and Safety Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97A.5 Cost Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97A.6 Workshop and Resource Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 99A.7 Lessons Learnt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Appendix B Central Jet Design Calculations 101

Appendix C Engineering Drawings 104

Appendix D Testing Notes 114

Appendix E Gaseq 121

Appendix F Flame Visual Analysis Results 124

Appendix G Pressure Calculations 130

Appendix H AS1210 - PT430 Tensile Strength 133

Appendix I RMSS 135

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Appendix J SOP for Start-up of Combustor 152

Appendix K SOP for Installation and Removal of Insulation 155

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List of Figures

1 Sequential Gas Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 NOx emissions vs process temperature [1] . . . . . . . . . . . . . . . . . . . . . . 83 CFD Simulation of MILD (Flameless) Combustion [2] . . . . . . . . . . . . . . . 94 MILD Combustion Furnace Images [2] . . . . . . . . . . . . . . . . . . . . . . . . 95 Regime Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Stability Regions of MILD Combustion . . . . . . . . . . . . . . . . . . . . . . . . 117 Layout of SCCT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Entropy vs. Enthalpy of both conventional and sequential combustion with the

same work outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Basic JHC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1610 Schematic of the Cabra Vitiated Burner . . . . . . . . . . . . . . . . . . . . . . . 1811 Adelaide Jet-in-Hot Coflow Burner . . . . . . . . . . . . . . . . . . . . . . . . . . 1912 Delft JHC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2013 Jet-in-hot crossflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2114 Schematic of the DLR JHC burner . . . . . . . . . . . . . . . . . . . . . . . . . . 2215 Overall Design of Original Combustor . . . . . . . . . . . . . . . . . . . . . . . . 2716 Mole Fraction of Methane at Varying Times and Temperatures . . . . . . . . . . 2817 Velocity contour plot in ZY plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918 Central Jet Tip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3019 Original Auxiliary Burner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 3220 Auxiliary Burner Concept Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 3321 Previous temperature distribution with and without honeycomb . . . . . . . . . 3522 Steatite flow conditioner failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3723 Experimental Testing Extension Tube . . . . . . . . . . . . . . . . . . . . . . . . 3824 Experimental Testing Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . 4025 Measurement Plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4026 Thebarton Piping and Instrument Diagram . . . . . . . . . . . . . . . . . . . . . 4327 Apparatus Plumbing Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . 4428 Auxiliary Burner Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5029 Radial Velocity Plots at the Jet Exit Plane . . . . . . . . . . . . . . . . . . . . . 5130 Radial Standard Deviation Plots at the Jet Exit Plane . . . . . . . . . . . . . . 5231 Radial Temperature Plots at the Jet Exit Plane . . . . . . . . . . . . . . . . . . 5332 Sliced Temperature Plots at Exit Plane . . . . . . . . . . . . . . . . . . . . . . . 5433 Radial Oxygen Plots at the Jet Exit Plane . . . . . . . . . . . . . . . . . . . . . 5634 Radial Carbon Monoxide Plots at the Jet Exit Plane . . . . . . . . . . . . . . . 5735 Oxygen and Temperature Profiles with Steatite Flow Conditioning System . . . . 5836 Flame Lift-Off Height versus Jet Reynolds Number . . . . . . . . . . . . . . . . . 6137 Lift-Off Heights vs. Jet Reynolds Number in the Delft burner . . . . . . . . . . . 6238 Standard images of jet flames at φ = 0.72 and T = 850◦C . . . . . . . . . . . . . 6339 Chemiluminescence Images of Jet Flames at φ = 0.72 and T = 850◦C . . . . . . 6340 Standard Images of Jet Flames at φ = 0.72 and T = 870◦C . . . . . . . . . . . . 6341 Chemiluminescence Images of Jet Flames at φ = 0.72 and T = 870◦C . . . . . . 6442 Standard Images of Jet Flames at φ = 0.72 and T= 940◦C . . . . . . . . . . . . 6443 Chemiluminescence images of jet flames at φ = 0.72 and T = 940◦C . . . . . . . 6444 Standard Photographs of Central Jet Flame at φ=0.72, Rejet=5000, O2 = 5.3% . 6545 OH* Photographs of Central Jet Flame at φ=0.72, Rejet=5000, O2 = 5.3% . . . 6646 Standard photographs at Rejet=5000 and 27kW . . . . . . . . . . . . . . . . . . 6747 OH* photographs at Rejet = 5000 and 27kW . . . . . . . . . . . . . . . . . . . . 6748 Mean oxygen content vs. radius for case 2 . . . . . . . . . . . . . . . . . . . . . . 6949 Schematic of Pressure Vessel Design . . . . . . . . . . . . . . . . . . . . . . . . . 72

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50 Heat transfer through pressurised combustor . . . . . . . . . . . . . . . . . . . . 74

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List of Tables

1 Previous JHC burners and experimental conditions . . . . . . . . . . . . . . . . . 172 Ring Burner Concept Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 Natural Gas Composition at Thebarton . . . . . . . . . . . . . . . . . . . . . . . 424 Nominal Accuracies For the Gas Analysis Equipment . . . . . . . . . . . . . . . . 465 Natural Gas and Compressed Air Flowmeters . . . . . . . . . . . . . . . . . . . . 466 Central Jet Testing Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 Central Jet Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 Coflow Testing Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 Ring Burner Concept Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4910 Temperature Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5411 Flame Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6012 MILD Jet Flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6813 Material properties used for heat transfer calculations . . . . . . . . . . . . . . . 73

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1 Introduction

The process of combustion has been pivotal to the advancement of human civilisation [3]. Despitethe development of alternative methods, combustion remains the dominant power generationtechnique and will continue to be so in the foreseeable future [3, 4]. However, it is not withoutcompromise; combustion inherently produces harmful pollutants [5]. Consequently, large-scaleuse of combustion for aeropropulsion and power production is a major contributor to climatechange. While the defining chemical processes are exceptionally complex, an increased under-standing of the driving mechanisms of the combustion process has allowed for improvements tobe identified and employed [6]. Integration of these improvements is gaining an increased focusas a means to decrease fuel costs and mitigate climate change. As a result, industries usingcombustion are in an opportune position to both leverage efficiency improvements and reducepollutant emissions to realise economic gains.

Gas turbines provide an efficient method of extracting thermal energy from the combustionof fossil fuels and are therefore the dominant tool for electricity production and currently theonly viable propulsion option for commercial aircraft. Technological improvements to materialsand the manipulation of the combustion process have led to efficiencies nearing 60%, howeverthe inherent decline of finite fossil fuels and environmental state requires further improvementsto be made [7]. The current method implemented to reduce harmful emissions and increaseefficiencies in turbines is lean premixed operation. However, integration in practical applicationsis limited by low reaction rates, extinction, instabilities and sensitivity to fuel and oxidantmixing [8]. While flame monitoring and re-ignition is possible, the integration of a regime freefrom instabilities would be advantageous. A method that delivers a greater degree of stability,lower pollutants and potentially higher efficiencies is MILD combustion.

The MILD combustion process is characterised by the oxidation of high temperature reactants ina low oxygen environment. The benefits of this particular regime include a higher energy releasealong with a distributed reaction zone producing a homogeneous temperature profile [9]. Thehigher degree of homogeneity results in a reduction in peak temperatures. If correctly harnessed,the higher energy release can increase the power output for a given fuel input and thereforeefficiency of the turbine while the uniform temperature profile will reduce the amount of thermalNOx produced. This technology has not yet been implemented in gas turbine applications asthe fundamental knowledge of its stabilisation mechanisms and its response to environmentalchanges necessary for its successful integration is absent.

MILD combustion is a promising technology for sequential combustion turbines as the tempera-ture and low oxygen exhaust created by the initial combustion is an environment similar to thatrequired by this mode. Figure 1 shows a basic schematic of a sequential combustion turbine. Theapplication of this regime could decrease pollutant emissions, thermo-acoustic instabilities andmaterial deterioration while increasing thermal efficiencies. However, a greater understandingof the conditions required to achieve a stable MILD reaction is necessary.

Previous work undertaken in 2013 as part of a fourth year honours project [10] resulted in thedesign and build of a testing apparatus to enable experimental research into the MILD regime.This consisted of an auxiliary burner to create the high-temperature, low oxygen coflow streamand a primary jet to implement the MILD regime. The testing results showed that MILDcombustion was not achieved, several components were identified to require modifications forthe successful generation of a MILD flame before data collection and analysis could be carriedout. The data of interest to this project includes coflow stream temperature, velocity, and gascomposition in addition to jet flame lift-off height and reaction intensities. Collectively, the data

1

Figure 1: Sequential Gas Turbine [10]

acquired will enable the formation of flame stability conclusions for this apparatus along withthe requirements for the development of a MILD flame.

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2 Background

2.1 Combustion

Combustion is the rapid chemical oxidation that occurs between a fuel and oxygen to producethermal energy [11]. Combustion will remain vital in the foreseeable future due increasingenergy demands owing to global population growth and rising living standards throughout thedeveloping world [3]. Currently, fossil fuels remain dominant as they are cost effective, energydense and abundant [12], [13]. In many applications, suitable alternatives to combustion areinferior. For example, batteries have been developed as an alternative to engines in motorvehicles, however the energy density is two orders of magnitude lower than liquid fuels [14].Renewable energy technologies have been developed to provide a cleaner avenue for energyproduction, however combustion remains a vital process in energy generation due to the existinginfrastructure and knowledge-base [15]. The focus of combustion research is to increase thethermal efficiency and reduce emissions [12].

For a combustion process to occur, an ignition source, fuel and oxidant are required. Fuel andoxidant quantities are adjusted depending application, this can be represented by the equivalenceratio (φ). This quantifies the fuel-air ratio present in a reaction, in relation to stoichiometricquantities [3], [16], [17]:

Φ =F/A

(F/A)st=

mf/ma

(mf/ma)st(1)

The stoichiometric quantity (φ = 1) is the minimum amount of oxidant that is required forcomplete combustion of the fuel [3]. The reaction is described as fuel-rich if the fuel-air ratiois greater than the stoichiometric quantity (φ > 1). Conversely, if the fuel-air ratio is less thanthe stoichiometric quantity, the mixture is fuel-lean.

Mixing at a molecular level is another prerequisite for combustion and effects reaction propertiesincluding pollution formation and safety [16]. The mixing can either occur prior to combustion(premixed), in the combustion reaction zone (non premixed) or a combination of these modes(partially premixed) [3], [17]. Soot formation is higher in nonpremixed combustion versus pre-mixed, as it forms when carbon molecules in the fuel become heated but are yet to react withthe oxidant. Despite lower soot formation, greater safety hazards are associated with pre-mixed combustion due to risk of flashback. This phenomenon occurs when chemical kineticsare faster than the fuel velocity, resulting in flame propagating back through the fuel deliverysource [18]. Flashback is undesirable as it threatens personnel safety and equipment integrity.Partial premixing is advantageous as it can be used to reduce the higher pollutant concentrationof nonpremixed or flashback hazards related to premixed combustion [3]. In addition to emissionformation and occurrence of flashback, mixing also influences the turbulence of the combustionreaction [16], [19].

Turbulent Combustion

Turbulent flows are prevalent in most practical applications and are unsteady, irregular andchaotic [16]. Turbulence is present from either the intentional mixing of reactants, or as a resultof the heat and expansion from combustion [3, 16, 19]. Turbulence contains a series of vortices,known as eddies, of different sizes and orientations [19]. The size of these eddies can be charac-terised using the standard length scales outlined below in decreasing order of magnitude [3]:L Characteristic width of flow or macroscale: determined by the system that the combustion is

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occurring in, for example the diameter of the combustion chamber`0 Integral scale or turbulence macroscale: similar order of magnitude to the largest length scale,characterising the mean size of the largest eddies in a turbulent flow`λ Taylor microscale: average rate of strain in a turbulent scale and has a much lower order ofmagnitude`K Kolmogorov microscale: smallest length scale and is used to define the point where kineticenergy is dissipated to fluid internal energyThe degree of turbulence in a flow can be represented by its Reynolds number, which is a theratio of viscous to inertial forces [19].

Re =ρV l

µ(2)

Where:ρ is the fluid density [kg/m3]V is the velocity [m/s]l is the characteristic length [m]µ is the dynamic viscosity[Pa.s]

As turbulent flows are prevalent in practical combustion systems, understanding the impactof turbulence on flow behaviour and reaction chemistry is important.The Damkohler numberis a non-dimensional parameter that represents the association between the turbulence and thecombustion:

Da =τflowτchem

(3)

Where:τflow is the lifetime of large eddies in the flowτchem is a chemical timescale based on a laminar flame

The Damkohler number is the ratio between the flow time scale and the chemical time scale and isused to determine the speed of the chemistry compared to the mixing rate of the reactants [16].It is also a key parameter when considering the interaction between turbulence and reactionchemistry in premixed flames. For Da< 1 diffusion occurs much faster than chemistry, hencea greater degree of mixing occurs before reactions between fuel and oxidant occur [16]. LowDamkohler numbers are currently seen in applications that operate with a high degree of exhaustgas recirculation [16], [20]. Fast chemistry (Da�1) means that the reaction rate is greater thanthe diffusion rate. The application of low Damkohler numbers is a current area of interest in newcombustion technologies due to the desirable properties such as lower combustion pollutants [20].

2.2 Flame Stability

Flame stability is of fundamental importance to combustion systems for control, safety, emissionsand efficiency. A stable flame is considered to be anchored at a desired location and resistantto both flashback and blow-off. Conditions for lift-off and blow-off are important considerations

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for the steady and efficient operation of combustion systems [3]. The proceeding terminologyare necessary for an understanding of flame stability.

Flame Speed

Essential to flame stability is the principle of flame speed. For the stability of a flame in aturbulent flow, the flame speed is required to match the local mean flow velocity. Flame speed isdefined as the measured rate of expansion of the flame front in a combustion reaction. It can bedescribed as the velocity at which unburned mixture enters the flame zone in a direction normalto the flame [3]. It is a key consideration as it dictates both the flame shape and behaviour suchas blow-off and flashback.

Lift-Off

The distance between the base of a lifted flame and the burner rim is termed the lift-off height.Higher fuel flow rates will tend to increase lift-off, and past a critical point will cause theflame to blow-off or extinguish [21]. Understanding the mechanisms behind lift-off in a MILDenvironment is fundamental for a better understanding of operational limits.

blow-off

Blow-off describes the scenario where the fuel velocity is greater than the flame speed, risingthe lift-off height and pushing the flame further downstream until a reaction can no longer besustained and the flame is extinguished. The fuel velocity that causes flame extinction is termedthe blow-off velocity [3].

Flashback

Flashback is the alternative scenario and is of concern in premixed flames, where the fuel velocityis significantly lower than the flame speed and the flame propagates in the reverse direction.Reducing the fuel flowrate can cause such stability problems, often occurring when the fuel iscut off. Flashback arrest devices are traditionally installed to prevent dangerous propagationalong the fuel line.

Autoignition

Autoignition describes the rapid evolution of heat when a combustible mixture undergoes achemical reaction, in the absence of an ignition source such as a flame or spark [6]. A uniqueautoignition temperature exists for each fuel.

Ignition Kernel

A flame or ignition kernel is the early stage of flame initiation during combustion. Provided thatthe kernel is not extinguished, flame propagation will follow [22].The understanding of kerneldevelopment mechanisms and propagation is important for the development of new combustiontechnologies.

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2.3 Combustion products

2.3.1 Carbon Monoxide

Carbon monoxide is both a toxic emission and an intermediate product in the combustionprocess. Complete combustion of hydrocarbon fuels generates the principle chemical productsCO2 and H2O. The combustion of hydrocarbons can be broken down into a two step process,firstly fuel is broken down into carbon monoxide, followed by the oxidation of carbon monoxideto carbon dioxide [3]. The oxidation of CO is described by equations 4 through 7.

CO +O2 → CO2 +O (4)

O +H2O → OH +OH (5)

CO +OH → CO2 +H (6)

H +O2 → OH +O (7)

The production of CO2 from CO relies on the availability of oxygen, mixing turbulence, andcontact time at high temperatures. Hence, when pockets of gas exist with insufficient time athigh temperatures and insufficient oxygen, carbon monoxide results as a final product in exhaustgases.

For the purposes of this research project, carbon monoxide was reviewed to determine thecompleteness of combustion and the effectiveness of the auxiliary burners. Along with visualobservations, it was used during the trial and error phase to determine the best performing ringburner design and configuration.

2.3.2 Hydroxyl Radical

The hydroxyl radical (OH) is a primary intermediate species for the combustion of any hydro-carbon fuel comprised of H2 −O2 reactions [23]. Hydrocarbon combustion in lean to moderatelyrich conditions is governed by two reactions:

H +O2 → OH +O (8)

CO +OH → CO2 +H (9)

Equation 8 is defined by a relatively high activation energy, and as such OH production occursprimarily in the mid-to-high temperature ranges [24]. The OH radical is a good tool for combus-tion diagnostics as it can provide information on flame mixing, propagation, ignition, structureand local extinctions. This is particularly true for the MILD regime where CH* luminosity isabsent. The chemiluminescence of OH* is a natural emission of light within the flame whenchemically excited OH relaxes from an upper electronic state to a lower electronic state. Hence,areas of high OH concentration are indicated by OH* chemiluminescence. Furthermore, OH*can be used to indicate high flame temperatures as OH* is formed within the high temperatureregion of a flame, and the mole fraction of OH* peaks at the maximum flame temperature [25].The OH* light emissions can be recorded using a chemiluminescence filter.

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Combustion Pollution

A paradigm shift that is characterised by sustainable energy production is vital given the fore-seeable environmental degradation. Pollution abatement is hence a top priority and currentcombustion in practical applications demands significant focus as the process forms a collectiveof harmful species. Nitrogen oxides (NOx), sulphur oxides (SOx), carbon dioxide (CO2), carbonmonoxide (CO) and soot negatively effect both human health and the environment [3]. Pollu-tion from these products is linked to temperature changes, unstable weather, and rising oceanlevels [26]. The simplified chemical equation for the ideal combustion of methane in air is:

CH4 + 2(O2 + 3.76N2)→ CO2 + 2H2O + 7.52N2 (10)

This equation illustrates the ideal reaction producing CO2, H2O and N2 however, in reality,other compounds are formed [26]. As aforementioned, NOx, SOx, CO and soot are additionalspecies produced during the combustion process which are undesirable. Emissions of NOx andSOx can produce photochemical smog and acid rain, CO and soot have been correlated toadverse health effects [3]. The formation pathways of these undesirable species are well known.This knowledge-base offers an opportunity to focus on improvements to practical applicationspertaining to the formation of pollutants.

Nitrogen Oxides

Each pollutant formed during combustion causes specific adverse environmental and healtheffects. Focusing on NOx is a high priority when considering mitigation strategies to reduceglobal warming, acid rain formation and smog [27]. Both nitric oxide (NO) and nitrogen dioxide(NO2) are combustion emissions, collectively referenced as NOx. NO is produced within thecombustion region, while away from the reaction zone, its presence leads to the formation ofNO2 [28]. The subsequent interactions of NO2 with oxygen can lead to the formation of ozone,causing adverse health effects. As NO is the predominant species formed in the combustion zoneand the precursor to the formation of NO2, its pathway is of particular interest. NO formationoccurs in three independent pathways; the Zel’dovich mechanism, the Fenimore mechanism andthrough the fuel source. Each pathway dictates a distinct type of NOx formed, being thermal,prompt and fuel NOx respectively. The creation of fuel NOx is dependent only on the presenceof nitrogen in the fuel compound and prompt NOx formation is linked to fuel rich systems. Theoptimisation of stoichiometric ratios and deliberate fuel choice have been used to curtail promptand fuel NOx respectively. The creation of thermal NOx however, is due to the oxidationof nitrogen molecules within a high temperature reaction region, leaving significant scope forthermal NOx abatement by deviating from the conventional combustion process.

The pathway for thermal NOx formation is endothermic and as such is strongly dependent ontemperature [29]. Due to the high activation energy of the mechanism, the formation of thermalNOx increases at an increasing rate at temperatures higher 1500◦C [28]. This can be seenfrom research performed by Wunning and Wunning [30], where considerable thermal NOx wasmeasured after seconds for temperatures above 1600◦C, and in milliseconds for temperaturesabove 2000◦C.

The formation of thermal NOx occurs in three steps and are shown in Equations 11 - 13. Therequirement for a strong N2 triple bond to be broken makes the first reaction the rate limitingstep. Due to the high activation energy required to separate these bonds, NOx production bythis mechanism proceeds at a slower rate and is very temperature sensitive. Reducing residence

7

times at high temperatures is therefore critical for NOx abatement [31]. Additionally, as is evi-dent by the Zel’dovich pathways, the concentration of available oxygen will significantly alter thereaction kinetics. This strong dependency of NOx production on both temperature and oxygenprovides an opportunity for the manipulation of thermodynamic and compositional parametersfor emission reductions.

N2 +O ↔ NO +N (11)

N +O2 ↔ NO +N (12)

N +OH ↔ NO +H (13)

2.4 MILD Combustion

One promising technology available to reduce thermal NOx emissions is Moderate or IntenseLow Oxygen Dilution (MILD) combustion. The reduction in NOx emissions compared to bothconventional and staged combustion is illustrated in Figure 2. The low NOx potential of MILDcombustion is due to the low maximum temperatures in the reaction zone [24]. In additionto NOx abatement, MILD is characterised by reduced soot emissions, a uniform temperaturedistribution in the reaction zone and an increase in process efficiency when compared to stan-dard combustion [28], [30]. The latter two features being drivers for implementation in furnaceenvironments, particularly within the steel making industry. The MILD regime is referencedusing various names, including: Flameless Combustion, Colourless Combustion, High Tempera-ture Air Combustion (HiTAC) or FLameless OXidation (FLOX R©). There are subtle differencesbetween each, but the precise demarcation is unclear.

Figure 2: NOx emissions vs process temperature [1]

The conditions required for MILD combustion to occur include depleted oxygen and high tem-perature reactants. Once these conditions have been met, the MILD regime can be identified

8

by a shift to a colourless flame and a reduction in temperature gradients [32]. This phenomenonis commonly demonstrated by using a well stirred reactor. Cavaliere and de Joannon [24] useda stoichiometric methane/oxygen/nitrogen mixture at an inlet temperature of 1100K and adecreasing oxygen molar fraction to demonstrate the relationship between dilution and temper-ature increase during combustion. While keeping the ratio of oxygen to methane (φ) constant,but decreasing the oxygen molar fraction from 0.2 to 0.05, the temperature change lowered from∆ T=1000K to ∆ T=550K. The MILD combustion regime being the latter case investigated.From this research, it is evident that higher thermodynamic efficiencies and reliability can berealised through the higher average outlet temperatures and lower maximum fluctuating tem-peratures in the regime. The narrow temperature variance is of particular interest for emissionsreductions and for applications where material reliability is significantly impacted by high peaktemperatures. The clear difference in temperature gradients can be observed through CFDanalyses in Figure 3 and furnace images in Figure 4.

Figure 3: CFD Simulation of MILD (Flameless) Combustion [2]

(a) MILD Combustion of Natural Gas (b) Conventional Combustion of Natural Gas

Figure 4: MILD Combustion Furnace Images [2]

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The operating range for MILD and other combustion regimes can be seen in Figure 5. The lowerhorizontal boundary illustrates that the temperature of the inlet reactants must be higher thanthe auto-ignition temperature of the fuel [24], while the vertical boundaries indicate the dilutionrequirements. Conventional combustion will proceed if the oxygen concentration is above 21%,whereas MILD combustion requires an oxygen concentration below 15%. Previous work on theregime has gone as far as applying the technology in steel, ceramic and glass furnaces [33].Extending the knowledge-base through research and development could allow the regime to beimplemented in a broader spectrum of applications. In particular, understanding the stabili-sation of flames and their operating regions is important. For oxygen concentrations between15 and 21%, it is known that an unstable, lifted region exists, threatening extinction. Dally etal. [34] researched the MILD mode by reviewing the flame structure while varying the oxygenconcentration from 9 to 3% in the exhaust gases. By reducing the oxygen level in the hot coflow,it was evident that the flame became less luminous and the temperature increase in the reactionzone was reduced to 100K. In particular, it was found that at 3% oxygen, a different chemicalpathway for NO formation was evident exhibiting reduced temperature dependence. Achievinga flameless reaction zone is non-trivial. In particular, understanding how to achieve a stableflame in a range of combustion applications requires in-depth understanding of the interactionsbetween oxygen dilution, temperature and the operational parameters of the system.

Figure 5: Dominant combustion regimes at varying oxygen and temperature combinations [35]

For furnace environments, the dilution and high temperature requirements are met by circulatinghigh volumes of exhaust gases containing large concentrations of inerts into the combustionzone. Figure 6 demonstrates the relationship between different combustion regimes in a furnaceenvironment and the exhaust gas recirculation [30]. The precise recirculation requirementsare described by the non-dimensional recirculation coefficient, Kv, which is the measure of thevolume of clean air to exhaust gases [28]. It is the ratio between the mass flow rates of therecirculated flow mR and the mixed flow mM , where the mixed flow is comprised of the massflow rate of the fuel mF and the air mA [36]:

Kv =mR

mF +mA(14)

10

What can be seen is that the MILD combustion region operates in wider range of tempera-ture and recirculation ratio combinations beyond the critical limits of conventional combustion.Furthermore, it is evident that the the transitional region between MILD and conventionalcombustion is unstable. If exhaust gases are above the auto-ignition temperature, but the recir-culation ratio is too low, the flame moves into an unstable region. If the furnace temperaturethen drops below the auto-ignition temperature of the fuel, then the flame will extinguish [28].This graph shows that a new combustion regime is established when recirculation rates aresufficiently high and operating temperatures are above auto-ignition. However, the specific tem-perature requirements and recirculation rates are variables dependent on application and arenot well understood or in practical combustor applications, which is the focus of this researchproject.

Figure 6: Stability regions of MILD combustion [2]

The low oxygen environment is essential for the formation of a distributed reaction zone, withhigh residence times resulting in low temperature increases and a uniform temperature distri-bution. The strong dilution lowers the reaction rate, facilitating a distributed combustion zoneas reactants are given more time to disperse before product formation [37]. Cavaliere and deJoannon [24] found that a distributed reaction zone is achieved with MILD combustion becauseits ignition time delay is longer than the fuel and exhaust gas mixing time, hence the Damkohlernumber is of the order of unity. Kumar, Paul & Mukunda [38] found that the spatial temper-ature variation in their combustor was 15% for MILD combustion and 51% for a classical jetflame. This dispersed structure enables a reduction in peak temperatures, a more stable flame,and an increase in efficiency [36]. Furthermore, the temperature profile homogeneity and a re-duction in peak temperatures reduces high amplitude pressure oscillations due to the steadierheat release. The high amplitude pressure oscillations are a result of the feedback loop fromchamber acoustics and heat release perturbations. These features are concerns for the conven-tional combustion processes as they threaten flame stability. Through the absence of a flamefront and a higher degree of uniformity owing to the distributed reaction zone in MILD com-bustion, they can be eliminated [1]. Furthermore, the presence of the pressure oscillations inthe conventional combustion process have a significant negative impact on the life of materialsdue to the high cyclic vibration amplitudes at elevated temperatures [39]. Understanding theapplication of MILD combustion within gas turbines would hence be advantageous to increasetheir lifespans.

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The application and implementation of the MILD combustion regime has been traditionallydominated by a focus on furnace environments. For such applications, significant gains havebeen shown in industry with regards to thermal efficiency and reduction in NOx emissions. Fur-thermore, improvements in the material treatment field, particularly in the steel industry, haveresulted from the MILD regime’s homogeneous temperature profile [24]. However, the efficiencyand environmental benefits of MILD combustion are not limited to furnaces. Understandinghow to initiate and sustain a stable MILD reaction zone in applications with more strict operat-ing parameters requires further experimental research. Particularly with regards to the stabilitylimits and extinction points.

2.5 Gas Turbines

Since their introduction, gas turbines (GTs) have revolutionised the power production andaerospace industries as they provide an efficient method of extracting energy from liquid andgaseous fuels. Their high reliability, versatility and power per unit volume means that thereis currently no viable alternative for propulsion of transonic aircraft [7]. However, with the in-creasing demand for electricity and the focus on climate change, improving the efficiency of GTsis of great importance to lower operational cost, the demand on scarce resources and harmfulemissions. These are currently conflicting goals, higher temperatures are required to improveefficiency however thermal NOx formation increases with temperature [31]. Significant develop-ments have been made to conventional gas turbines to improve their efficiency and reduce theemission outputs, however in their isolated form, efficiency limits are being approached withcurrent efficiencies of approximately 40% [40]. For this reason, technological improvements thatenable higher power densities with concurrent emission reductions are gaining attention. Currentpractices include altering the air-fuel mixtures as well as staging the combustion and recoveringlatent heat. While these practices improve the operation of gas turbines, avenues still exist fromwhich exploration could yield significant benefits.

Simple cycle combustion turbines (SCCT) consist of compression, combustion and exhauststages, shown in Figure 7. The compression and combustion stages increase the pressure andtemperature of the working fluid, the energy is extracted by the turbine before exhaust gasesexit. While the operational parameters differ between aeropropulsion and ground based GTs,the fundamental design is the same and therefore both suffer from the same instabilities. Theseinclude pressure fluctuations, unburnt hydrocarbon emissions and flame instabilities [7].

Figure 7: Simple Cycle Combustion Turbine Schematic [41]

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A common stability issue with GTs is the combustion pressure oscillations that occur withinthe combustion chamber. These oscillations are a result of a feedback loop produced by thenon-uniform release of heat creating sound waves and fluctuations in velocity and pressure, thusfurther perturbing the heat release [39]. This coupling causes major combustion instabilitiesin the system and the effects are mechanical vibrations and possible flame blow-off. Mechan-ical vibrations produce cyclic loading in the GT and can cause undesirable fatigue in turbinecomponents, reducing lifespan and possibly resulting in catastrophic failure [42]. Combustionpressure oscillations occur in both ground based GTs and aeropropulsion, however the effectscan be more catastrophic in air-based applications where reliability is a major safety concern.

Increasing thermal efficiency of gas turbines, along with reliability, is another area that requiresfurther research. Thermal efficiency of SCCTs is improved by increasing the temperature ofthe working fluid within the combustion stage of the cycle, however metallurgical tolerancesof the alloys in the turbine limit the allowable operating temperatures [43]. Potential energyin the form of pressure carried by the working fluid is converted to usable work by turningthe turbine rotors. Hence, to increase power output, the pressure drop over the turbine mustbe raised. This can be achieved by raising the compression ratio of the turbine or increasingTurbine Inlet Temperature (TIT) through combustion. Smith et al. [43] state that an increase offiring temperature of around 55◦C increases the power output by 10-13% and raises the thermalefficiency by 2-4%. The TIT is however limited by loss of material strength of the turbineblades that results from operating temperatures nearing the melting temperature of the alloy.While modern alloys have allowed TITs to be increased to temperatures of around 1800K [7],overall thermal efficiency of simple cycle turbines still remains at around 40%, hence scope forinvestigating cycle improvements exists.

Alterations to the combustion modes of simple cycle turbines have been developed to increaseperformance pertaining to efficiency and emissions. Common combustion modes include leanpremixed combustion, combined cycles and sequential combustion [7]. The Lean PreMixed(LPM) combustion regime involves mixing the air and fuel before entry to the combustor, LPMeffectively reduces the flame temperature inside the combustor and hence reduces thermal NOx

emissions [43]. Combined Cycle however uses latent heat in the exhaust stream of a turbineto increase the cycles’ thermal efficiency. By preheating other substances, such as water in aseparate cycle, the overall thermal efficiency of the two cycles is improved to values nearing60% [7]. Similarly, Sequential Combustion GTs improve the thermal efficiency by preheatingthe working fluid of another cycle. This is achieved through introducing a second combustionand turbine stage to the SCCT cycle. The initial combustor burns a portion of the fuel mixture,the energy is extracted and then passed through the reheat combustor where the remaining fuelmixture is burnt and the energy extracted. The advantage of sequential turbines is that throughburning the fuel mixture twice, the TIT of each turbine is lower than that of a conventionalturbine for the same power output [44].

Sequential gas turbines are currently available for the industrial power generation market. Theinitial combustor heats the compressed air using around half of the fuel, the combusted gasesthen expand through the high-pressure turbine. Cooling air is added to the exhaust gases andcombusted again, after which they pass through a second high-pressure turbine. The secondstage of combustion does not require an ignition source as the gases are above their autoignitiontemperature, making the combustor more stable. When compared with conventional turbines,given the same specific power output, a lower TIT is achieved (Figure 8) [44]. The advantagesof this turbine layout are reduced O2 and increased H2O levels in the second combustor leadingto lower TITs and flame stabilisation through autoignition [44]. These factors all contribute tolowering the NOx produced.

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The initial combustion stage consumes some of the available oxygen resulting in a reducedamount in the second chamber. This reduced oxygen level lowers the peak temperatures duringcombustion and hence limits the formation of NOx. Furthermore, additional CO2 and H2Oincrease inert concentration, reducing the peak flame temperatures. A reduction in peak flametemperatures is not only advantageous to the life of the turbine components, but also ben-eficial for emission abatement due to the relationship between thermal NOx production andtemperature [24].

Figure 8: Entropy vs. Enthalpy of both conventional and sequential combustion with the samework outputs [44]

While Sequential Combustion GTs provide lower NOx emissions and lower TITs, improvementscan still be made to increase performance. The cooling air added before the second stage ofcombustion reduces net power output. Therefore, improvements to the thermal efficiency ofsequential gas turbines are possible through omitting the additional cooling air.

Gas Turbines for both power production and aeropropulsion could benefit from the lower emis-sions and higher stability of MILD combustion. In particular, the second stage of sequentialGTs could make use of MILD combustion as the conditions presented in this stage of combus-tion are similar to that required for the MILD regime to occur. The dispersed reaction zonecharacterising this regime abates large pressure fluctuations, hence reducing the thermoacousticinstabilities associated with lean-premixed combustion [30]. Furthermore, the reduction in peaktemperatures and lower temperature fluctuations enable the turbine to be operated at higheraverage outlet temperatures, increasing the thermal efficiency of the system [24]. These benefits,along with the reduction in NOx formation, make MILD combustion a promising technology forgas turbines.

Despite the advantages of MILD combustion, little is known about the stability of the reactionzone at high pressures. It has been shown that MILD combustion can successfully reduce NOx

in gas turbine combustors. Duwig et al. [45] exhibited low NOx emissions, below 10ppm, at at-mospheric conditions however pressure fluctuations were also recorded indicating that the MILDcombustion regime had not been reached. Additionally, Flamme [46] presented emissions below3ppm at atmospheric pressure and 15% O2 content. Luckerath et al. [37] operated a FLOX R©

combustor at 15% O2 content and pressure of 20 bar and found the NOx emissions and operatingtemperature range improved with an increased fuel nozzle velocity. These studies indicate that

14

the MILD combustion regime could reduce NOx emissions in a gas turbine environment howeverthe stability of the regime needs more investigation before it can be successfully applied.

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3 Prior Work

The study of nonpremixed flames in vitiated coflow has been the subject of extensive researchto further understanding of flame stability in combustion systems using exhaust gas flow [23,47–49]. Previous experimental and computational research has focused on jet flame stability ina series of coflow environments and jet conditions at atmospheric pressure. To emulate vitiatedcombustion conditions in a controlled environment, a jet issuing into a hot coflow is commonlyused, the basic design of which can be seen in Figure 9. The inclusion of a secondary burnersystem upstream of the jet allows the chemical kinetics to be decoupled from the complexrecirculating flows that are often present in practical applications. The described arrangementdoes not completely replicate actual practical systems, but mimics the basic environmentalparameters and independent control of parameters, enabling the decoupling of input variablesWhile analysis at atmospheric pressure is imprecise, an open jet exit plane provides greateraccess to experimental data, particularly critical optical diagnostics.

Presented in this section are relevant and recent analyses of jet flames issuing into a vitiatedcoflow or crossflow environments. The experimental JHCs used in each study were operatedunder MILD conditions with the exception of the research undertaken by Cabra where excessoxygen was maintained above the commonly defined MILD range. The major parameters alteredwere the temperature, velocity and excess oxygen of the coflow and the velocity or Reynoldsnumber of the jet. The overall objective of the studies reviewed was to increase the understand-ing of the stabilisation mechanisms for jet flames in diluted and preheated flows. The differencesbetween the studies lie in their area of focus, fuel type, apparatus details, measurement tech-niques and ability to decouple input parameters. Information displayed in Table 1 highlightsthe key parameters of each research study.

Figure 9: Basic Jet-in-hot coflow design [23]

3.1 Cabra Vitiated Burner

In 2002, Cabra et al. [47] presented results on a vitiated coflow burner, operating both hydro-gen and methane jet flames in an environment of hot combustion products. The study aimed

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Table 1: Previous JHC burners and experimental conditions

JHC Burner Fuel XO2 [%] Tcoflow(K)

Vcoflow[m/s]

ReJet

Cabra vitiatedcoflow

CH4 12 1350 5.4 23,600

Delft jet-in-hotcoflow

Natural gas(81.3% O2)

8.4 & 9.5 1395-1540 4.34.6

3,0009,500

Adelaide Natural gas(92% O2)diluted withH2

3 & 9 1100 2.3 5,00010,00015,000

Cross flow CH4 5.7-8.7 1234-1997 1.67-2.76 1,9145,0088,050

DLR burner CH4 10.1-13 1250-1550 10,000-30,000(Reynolds)

0.3 (m/s)

to further understand the stabilisation mechanisms of lifted turbulent jet flames in a coflow of12-15% excess oxygen, emulating mixing and chemical kinetics in the recirculation region ofadvanced combustors. The Cabra burner, shown in Figure 10, consisted of a jet in a cylindri-cal chamber directing exhaust gases from a lean premixed flame to the upstream jets reactingzone. Consideration was taken to ensure the burner diameter was greater than the jet diame-ter to avoid the entrainment of the surrounding air, enabling the research to be modelled as atwo stream problem. The research project observed jet flame behaviour with changing coflowand jet fuel flow conditions. By undertaking a series of parametric experiments and compu-tational assessments, the sensitivity of flame lift-off height to jet velocity, coflow velocity andcoflow temperature was reviewed. Noteworthy is the realisation that all chemical kinetic activityoccurred in regions associated with higher temperatures, lower coflow velocities and lower tur-bulence intensities, highlighting the degree of jet sensitivity to coflow environment rather thanjet velocity. Furthermore, experimental results found that all parameters (jet velocity, coflowvelocity and coflow temperature) influenced the lift off height, but the greatest sensitivity wasto the coflow temperature. Specifically, a 5% drop in co-flow temperature was found to roughlydouble the lift-off height. While this work greatly broadened the understanding of jet flames invitiated coflow, the excess oxygen levels analysed are generally not considered to be conducivefor MILD combustion. Hence similar work is necessary for a lower excess oxygen environmentto understand how the aforementioned parameters alter a MILD jet flame.

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Figure 10: Schematic of the Cabra Vitiated Burner [47]

3.2 Adelaide Jet-in-hot coflow burner

Medwell et al. [50] reported on experimental research undertaken on turbulent nonpremixed jetflames in a hot, diluted coflow that emulates the defined MILD conditions. They undertook theexperimental study using CH4/H2 as the jet fuel at three different Reynolds numbers withina coflow of two oxygen levels (3% and 9%). By using planar laser-induced fluorescence andRayleigh scattering laser diagnostic techniques, the spatial distributions of the hydroxyl radical,formaldehyde and temperature were recorded at 35mm and 125mm above the jet exit. Thesemeasurement locations were chosen to represent two different oxidant streams, at 35mm purelycoflow and jet fuel mixing occurs, while at 125mm external air is entrained in the flow. Figure 11shows the JHC burner design, and as aforementioned it follows similar design principles to theOldenhof and Cabra burner. Nitrogen was injected through the secondary burners to maintaina constant mass flow rate, and hence decouple the effects of oxygen from temperature. Datareviewed found that at the jet exit a reduction in O2 led to a reduction in the hydroxyl radicaland a greater OH distribution due to an increased volume of oxidant stream being required forfuel consumption. At the downstream location it was found that entrained external air withhigher O2 levels partially premixed with the jet fuel, causing cooling of the flame and localextinction pockets at 3% oxygen. At 9% excess oxygen the flame front was weakened, but notextinguished, and oxygen leakage from the surrounding air cause OH and temperature levels toincrease. These features indicate a deviation from MILD combustion. For practical applicationsthe entrainment of external air is unlikely, however, this work demonstrates the MILD flamesensitivity to variations in the coflow environment. Furthermore the importance of homogeneous

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mixing of coflow and jet fuel has been highlighted as a key criteria for the stability of a MILDflame. Consequently, a uniform and axisymmetric coflow conditions is principle objective forfuture studies and final integration into combustion systems.

Figure 11: Adelaide Jet-in-Hot Coflow Burner [50]

3.3 Delft Jet-in-hot coflow burner

A comparable burner was used for the study of MILD combustion at Delft University by Oldenhofet al [49]. Similarly to the Adelaide burner, the Delft-in-hot coflow burner consisted of a centralinsulated jet open to the atmosphere, and burners upstream with the primary function of creatingexhaust gases. The most significant difference is the absence of nitrogen injection to decouplethe effects of the coflow temperature and oxygen concentration. Through flame luminescenceand OH-PLIF measurements, flame behaviour was observed at different jet Reynolds numbersand coflow conditions. By reviewing luminescence images, it was found that the stability ofMILD lifted flames differ from conventional lifted flames. While conventional flames remainstable through propagation, auto-ignition from the development of ignition kernels maintainsstability of the Delft jet in hot coflow flames. Unique behaviour was also identified in MILDflames, in respect to the relationship between Reynolds number and the first ignition events.Contradictory to expectations, increasing the jet Reynolds number initially decreases the axiallocation of auto ignition kernels. Conclusions were made assuming a large correlation betweenthe rate of co-flow entrainment. The entrainment flux is proportional to the centreline velocityof the jet, and hence as the velocity increases, the transport of hotter co-flow fluid occurs froma larger radius. The temperature gradient in the coflow therefore bears significant influenceover the height at which reactions initiate above the jet exit plane. These findings are notdissimilar from the Cabra study, finding the strongest linkage between the stability of flamesand coflow temperature. This research suggests a strong dependence of MILD flame stabilityon the uniformity and symmetry of the coflow temperature.

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Figure 12: Delft Jet-in-hot coflow burner (reference required)

3.4 Jet-in-hot Crossflow burner

A comparable study was presented by Sidey and Mastorakos [51] on the behaviour of methanejet flames in a turbulent cross-flow environment of conditions characteristic for MILD combus-tion. Like parallel flowing vitiated burners, the effect of co-flow temperature, velocity and jetvelocity were considered. The experimental apparatus can be seen in Figure 13, illustrating theorthogonal fuel injector above a premixed burner base, alumina foam for flow conditioning andtwo injectors for air and nitrogen injection. Both air and nitrogen were injected separately to toobserve different flame behaviours for three scenarious, additional air, dilution with N2 and pureexhaust gas coflow. The jet flame was studied at all conditions to reveal changing auto-ignitionlocation and kernel appearance frequency. Results showed that with higher N2 dilution, the jetfuel auto-ignites further downstream, shown by delayed kernel formation, which is a similar find-ing to other parallel JHC arrangements. Furthermore, time-averaged OH* chemiluminescenceimages showed that the flames considered to be within the defined MILD range were significantlyaffected by decreasing cross flow excess oxygen, primarily changing the reaction zone size andintensity. As illustrated in Table 1, this cross flow studied was extensive and observed flamebehaviour clearly within the MILD region. Hence, a study with similar depth in a parallel ar-rangement could be of significant benefit for comparative purposes and so that results acquiredfor the MILD range can be reviewed.

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Figure 13: Jet-in-hot crossflow [51]

3.5 DLR JHC

The afeormentioned studies presented insights and statistics on the role of coflow environmentalparameters, jet velocity and entrainment on lift-off height, kernel formation and propagationand extinction. Research undertaken by Papageorge et al. [52] focused on the role of turbulenceand turbulent mixing and the causation behind intermittent ignition kernel locations. Throughthe use of experimental tools capable of measuring mixture fractions and temperature fieldsprior to and through the onset of auto-ignition, the governing dynamics pertaining to the effectsof molecular and thermal mixing and mixing rates were analysed. Unlike other studies witha similar experimental focus, the central jet surrounded by a hot vitiated coflow issued fuelin a pulsed manner. The pulsed nature of the jet was included as only the time from fuelrelease until autoignition was of interest. A high-energy pulse burst laser system allowed forhigh-speed planer Rayleigh scattering imaging and the determination of the mixture fractionand temperatures fields. The complete experimental arrangement is shown in Figure 14, wherea hot, vitiated coflow was generated from a premixed hyrdogen/air flame and a bronze-sinteredmatrix was used for the cooling of the central jet. To minimise coflow heat loss through thecooling system, a bulk coflow velocity was maintained at 4m/s. The oxygen concentration andcoflow temperature were controlled by varying the equivalence ratio of the premixed reaction,unlike the Adelaide burner the effects of these two parameters were not decoupled. The sampleresults that eventuated showed that the turbulent ignition delay times were much greater underturbulent conditions than laminar, homogeneous reactor conditions. This indicates the influenceof transport and strain and scalar dissipation rates have on mixing processes. Furthermore, auto-

21

ignition was found to occur under lean conditions at the periphery of the fuel jet, where thelocal mixture fraction was less than the stoichiometric mixture fraction.

Figure 14: Schematic of the DLR JHC burner [52]

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4 Aims

Research is required to fully understand the behaviour of a MILD flame and its response toenvironmental changes. This combustion regime has the potential to increase thermal efficiencyin practical systems and reduce NOx emissions and is therefore can be financially and envi-ronmentally beneficial to the gas turbine industry. Prior work on this project resulted in themanufacture of a JHC apparatus, however modifications are required to facilitate a MILD flameand allow data collection in a controlled environment. The overall aim of this project was tocreate an environment within which a MILD flame could be established and to observe andanalyse the effects of jet fuel velocity, coflow temperature and coflow oxygen content on thestability of a jet flame.

The project contains design and build and experimental phases and so the goals have been di-vided accordingly. At a minimum, it is an expectation of the stakeholders that the primary goalsbe successfully completed. If time and resources permit and no major setbacks are encountered,the extension goals will also be realised.

4.1 Primary Goals

4.1.1 Design Goals

1. Weaknesses were documented relating the testing apparatus preventing a MILD flamefrom developing. Therefore, a review of existing apparatus to confirm and understandthese weaknesses is necessary to determine design specifications for modifications. Thisgoal is to be completed by the group by early March to allow sufficient time to completethe modifications.

2. Redesign and build the central jet to:

• Eliminate the possibility of compositional changes to the fuel delivered tothe reaction zone, ensuring that interpretation of results are accurate. De-signs will be created for methane as the primary fuel used in the apparatus.For this reason, 1100K was identified as the maximum allowable fuel tem-perature.

• Reduce asymmetrical disturbances to remove modelling complexities andimprove the capacity for result interpretation.

• Introduce adjustability for improved flame observability given the visualaccess for flame observations is limited by the viewing pane in the combus-tor. 200mm vertical adjustment was deemed appropriate for analysis andcomparison of the flame lift-off and reaction intensity.

Designs will be finalised by the end of March and the manufacturing by the end of June,so that full commissioning and testing can be initiated during July.

3. Redesign and build the auxiliary burners to supply an adequately uniform coflow, andproduce the hot, oxygen-diluted flow required to facilitate the MILD regime. This design

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task shall be completed by the end May for the manufacturing and commissioning to occurin June.

4. The flow conditioner originally installed improved coflow uniformity, however was not ableto withstand the operating temperatures. Consequently, if the auxiliary burners producean asymmetric or highly turbulent flow, an improved conditioner must be designed. Uni-formity and laminar flow is desirable for modelling accuracy, repeatable data acquisitionand for meaningful conclusions to be drawn. Previously measured peak temperatures of1623K necessitate a system that can withstand temperature greater than this. An investi-gation into design options is to be completed by May, with a final concept being consideredon the condition that there is a requirement for coflow improvement.

4.1.2 Experimental goals

1. Perform a study on a series of auxiliary burners to select a suitable burner arrangement forthe creation of a low-oxygen, high-temperature environment required for MILD combus-tion. Furthermore, the burners should be operational over a range of air/fuel ratios andflowrates. The selection process will be completed through an initial qualitative analysisfollowed by a numerical validation. Numerical analysis will consist of the production ofradial profiles of the coflow stream as collected at the jet exit plane. The data of interestincludes:

• Oxygen and carbon dioxide species concentration

• Temperature

• Mean velocity and velocity fluctuation

2. Complete a qualitative visual analysis of the central jet flame at varying coflow excessoxygen, bulk velocity and temperature. By using standard photographs and OH* chemi-luminescence images the following features will evaluated:

• Lift-off height

• CH* intensity

• OH* intensity

• Flame base characteristics

• Reaction zone gradient

4.2 Extension Target

Initiate the design calculations required for the design and build of a pressurised gas turbineexperimental burner to enable future data acquisition under a pressure of 5 bar. Determiningthe stability of MILD combustion in a pressurised environment is important as pressure affectsparameters that are critical to stability such as flame speed which is inversely proportional to

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the square of pressure.

This goal will be commenced by the group once the experimental goals have been realised withthe aim of completion by the 15th of October. This will provide sufficient time to includepressurisation calculations into the final report.

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5 Combustor Design

As highlighted in Section 2, the stability of MILD combustion in a jet-in-hot coflow arrange-ment is an area of combustion science that requires greater focus, both within atmospheric andpressurised environments. Through this broadening of knowledge, the integration of the MILDregime in practical applications may be realised. Prior work on this research project involvedthe design and build of an enclosed jet-in-hot coflow burner arrangement for analysis underpressurised conditions. The design was based on the jet-in-hot coflow arrangements outlinedin Section 3. The Cabra, Oldenhof et al. and Adelaide burners produce hot, dilute exhaustgases using a partially premixed burner upstream of a central jet. Through this arrangement, avariable exhaust environment may be generated that is required for a MILD flame to evolve.

The initial objective of this project encompassed a redesign phase of components that showedflaws during previous testing. Through the design of these elements, an experimental testing pro-gram was initiated and data acquired for interpretation. Presented in this section is an overviewof the original design, component weaknesses and their modifications based on a formulateddesign criterion, complete drawings of the modified parts are in Appendix C.

5.1 Original Design

Sequential combustion turbines operate by burning approximately 50% of the total fuel in thefirst turbine division, where most of the heat energy is extracted by turbine blades before theexhaust gases flow through to the second division. After this process, the exhaust gases areleft at elevated temperatures low oxygen. The purpose of a jet-in-hot coflow arrangement isto analyse the behaviour of a jet flame in a vitiated coflow, similar to the environment createdafter the initial combustion stage of a sequential turbine. A typical JHC consists of a burnerto increase temperature and reduce oxygen in the coflow followed by jet releasing fuel into theatmosphere for flame observations. Previous work on this experimental study resulted in thedesign and build of a JHC, however deviating from a typical design, the system was enclosed in achamber for its eventual pressurisation. The benefit of pressurisation is the response of a MILDflame to pressure may be observed and analysed along with other variables such as turbulence,velocity, temperature and oxygen concentration. Through this analysis, the exact conditions thatfacilitate the evolution of a MILD flame and identify the primary stability mechanisms. Theconclusions of this research can then be drawn on for the integration in sequential combustionturbines.

The combustor built previously for this research project, detailed in Figure 15, was comprised oftwo auxiliary burners and a primary jet enclosed in a stainless steel cylinder. The auxiliary burn-ers were designed to create the low-oxygen, high-temperature environment required to establisha MILD flame. The burners in the apparatus were designed to operate in premixed-mode, eachbeing supplied with a controllable fuel and air supply. Additional air was provided through theair manifold located at the base of the combustor. Depending on the flowrates of fuel and airsupplied to the auxiliary burners, the flow of exhaust products created could be highly turbulent,emphasising the requirement for a flow conditioner to reduce large-scale turbulence and improveuniformity.

The primary jet was designed to operate in nonpremixed mode and therefore only required afuel supply. The jet was located in the upper section of combustor. Finally, a viewing windowwas incorporated into the combustor wall for visual access to the flame, a requirement for flame

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analysis.

The selection of the combustor material was a compromise between availability, manufactura-bility and high melting temperatures. However, given the high temperatures and quantity ofoxidant within the combustor, it was acknowledged that high-temperature corrosion may be anoperational complication but other, more suitable materials were not viable due to the budgetand timeframe of this project.

Several design weaknesses were identified in the previous design limiting the evolution of a MILD.The weaknesses and their solutions are detailed in the subsequent sections.

Figure 15: Overall Design of Original Combustor

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5.2 Original Design Weaknesses

Design flaws in the original apparatus both prevented the evolution of MILD combustion andproduced adverse conditions for modelling and precise data analysis. Three focal areas wereidentified to require improvement, being the fuel jet, auxiliary burners and flow conditioner.The auxiliary burners successfully generated sufficient heat and and oxygen content for theevolution of a jet flame, however a MILD flame did not develop. Furthermore, despite exten-sive benchmarking during the design phase the coflow generated by the physical burner wasnon-uniform and inconsistent. These inconsistencies are the result of the unavoidable varia-tion between design and manufactured product, and can inherently cause future modelling andanalysis difficulties.

The installed jet consisted of a single stainless steel tube, bent at a right-angle and was designedto enter the primary combustor section through to the chamber wall. Original design specifi-cations focused on a variable fuel delivery velocity for the analysis of the relationship betweenflame lift-off and Reynolds number. While these objectives were met, intrinsic performanceissues limited the scope of experimental research. The following issues were identified:

Fuel compositional changes

The maintenance of a known fuel composition is critical for formulation of credible relationshipsbetween results input parameters. Furthermore, for modelling accuracy, it is essential that thedefined input conditions resemble the physical system. Natural gas (92% CH4) was the fuelchosen for delivery into the coflow stream for the evolution of a jet flame for its availability andits high commercial use in gas turbines. The jet was not insulated or protected from the hotcoflow environment and therefore acted as a heat exchanger between the hot coflow and thecool fuel. As a result, the fuel was heated by the coflow. Intramolecular bonds can break athigh temperatures, for methane this causes a decompositional change into hydrogen and carbon.The decomposition process of methane is illustrated in Figure 16, where a reduction in molefraction CH4 is plotted against a 60 second window for temperatures between 1100K and 1400K.Temperatures below 1100K so not show significant decomposition, however exceeding 1100K,CH4 rapidly changes composition. Peak temperatures reached in the original combustor designwere recorded at 1623K [10]. Consequently, the fuel issued into the primary chamber may havebeen heated above 1100K and therefore be of unknown composition.

Figure 16: Mole Fraction of Methane at Varying Times and Temperatures

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Coflow disturbance

Uniformity is a highly desirable characteristic of the coflow as it directly affects the flame be-haviour and ease of modelling. Therefore, any asymmetric disturbances in the flow need to beaccounted for in the analysis of results. The side-entry of the jet caused disturbances to thevelocity and temperature distributions of the coflow. The effects of the tube are illustrated inFigure 17, it is evident that the velocity is significantly reduced directly after it passes over thedelivery tube. Furthermore, the tube acts as a heat exchanger between the hot coflow travellingaround tube and the cool fuel travelling within it. Therefore, as the fuel is heated, the coflow isalso cooled, affecting its temperature uniformity.

Figure 17: Velocity contour plot in ZY plane

Lack of adjustability

During commissioning and testing of the original fuel jet, it was obvious that the fixed location ofthe jet exit restricted observability of the flame. Flame analysis drawing from visual observationsis essential to the study of flame stabilisation, hence variable flame observability is an importantfeature. For example, the flame lift-off height is of particular importance in determining thestability of a flame. Enabling adjustability of the jet ensures that the full lift-off height may beobserved.

5.3 Design Modifications

Design modifications were developed for the three areas where weaknesses were identified. Theconcepts and their justifications are presented in their respective sections.

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5.3.1 Primary Jet

Design Specifications for improved Jet

The primary jet design was developed using specifications formulated through a review of pre-vious design weaknesses and similar experimental arrangements. The specifications were segre-gated into primary and secondary groupings, where the former includes essential requirementsand the latter desirable. From the criteria outlined below, an appropriate concept was chosenfor manufacture.

Primary Specifications

• Delivery of fuel to coflow stream

• The temperature of the fuel at the jet exit should not exceed 1100K

• Tube length greater than 100 diameters to ensure fully developed flow [53]

• Adjustable jet velocity between laminar and turbulent at exit

• 200mm height-adjustability below the jet exit plane

• Reduce asymmetric interference with the coflow stream

Secondary Specifications

• Avoid permanent assembly for possible future design reevaluation

• Low cost

Final Design and Justification

To prevent the fuel from heating above 1100K and incorporate height-adjustability, the centraljet was designed to enter from the base of the combustor and was encased by a heat exchanger.The heat exchanger consisted of two concentric tubes around the jet using water as the workingfluid, similar to the cooling tube successfully used by the Delft University. A 7.5◦ conical sectionwas used to reduce the diameter from the outer tube to the central jet tube, this can be seen inFigure 18. Swagelok R© tee pieces were used for the water inlet and outlet.

Figure 18: Central Jet Tip

The jet assembly was held in place by an o-ring and a chamfered plate with four bolts to adjustthe compression applied by the o-ring. The plate was bolted to the existing air manifold whichrequired minor modifications. This simple mechanism was adequate for holding the jet at the

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desired height and could be adjusted easily.

The central jet was required to be adjustable between non-turbulent, transitional and turbulentoutlet at exit. A Reynolds number of 104 was identified as fully turbulent outlet conditions [54],this was used along with the known natural gas supply rates to calculate that the maximuminner diameter of the jet was 4.91mm (see Appendix B for full details). Comparing this with theavailable stainless steel tubing, 1/4” tubing was used for the central jet with an inner diameterof 4.55mm.

Potential Design Issues

The primary fuel injector has been designed to eliminate a known problem with its functionality,however the solution chosen could consequently create other problems. The cooling systemdesigned for the primary fuel injector will maintain a low fuel temperature, however it will alsoinherently thermal boundary layer around the jet. Hence, modelling of the fluid flow aroundthe pipe will need to incorporate the non-uniform temperature profile. While undesirable, it isan unavoidable result. Thermal insulation may solve this problem but was not installed as thechange in diameter near the jet exit would cause the fluid to become unattached.

Water was selected as the cooling fluid for the heat exchanger for its availability and high thermalcapacity. The disadvantage of water is that, if not kept cool, will change phase, thus altering isthermal properties. To avoid this, the water temperature at outlet was monitored throughoutoperation and flowrate adjusted to maintain a low temperature.

5.3.2 Auxiliary Burner

The fundamental objective of the auxiliary burner is create exhaust gas conditions sufficientlyhigh temperature and oxygen diluted for a MILD flame to evolve. The overall focus of this long-term research is to identify an operating window of a MILD flame for the eventual integrationinto a sequential combustion turbine. The partially premixed flames generated by the burnertherefore need to be stable over a range of velocities and air/fuel ratios. Furthermore, uniformityof the coflow stream at the jet exit plane is a requirement for both ease of result interpretationand future modelling. This requirement cannot be met, however, due to the thermal boundarylayer produced by the heat-exchanger incorporated into the central jet design. Therefore, acoflow profile symmetric about the central jet is a realistic goal. This section outlines theproblems with the previous burners, the specifications for an improved design, and details of theconcepts generated.

The original auxiliary burners comprised of two separate annuli, supplied by a central fuel-delivery tube, as shown in Figure 19. The design of the improved central jet required a clearpathway through the core of the combustor, therefore preventing the previously-manufacturedauxiliary burners to be used. Additionally, the previous burners produced high temperaturevariance at the jet exit plane, therefore the redesign process was an opportunity to improve thecoflow uniformity.

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Figure 19: Original Auxiliary Burner Design

Primary Specifications

Based on previous design weaknesses and fundamental requirements for this experimental anal-ysis, the following primary and secondary specifications were generated:

• Produce a low-oxygen coflow stream

• Produce a coflow stream at temperatures exceeding the autoignition temperature of methane,accounting for heat loss through the combustor.

• Capacity to operate in a partially premixed mode

• Stable operation over a range of air/fuel ratios of interest to the experimental research

• Stable operation over a range of air/fuel flow rates

• Withstand temperatures up to 1623K (based on peak temperature previously recorded inthis apparatus)

Secondary Specifications

• Attach to the combustor using 3/8” Swagelok R©

• Can be manufactured from materials available from The University of Adelaide MechanicalWorkshop supplies.

Concept Designs

A trial-and-error approach was adopted to the design and testing phases of the auxiliary burnersbecause of the lack of a blueprint model and the inconsistencies related to fabrication that madeasymmetry unavoidable. Therefore, burners with varying hole sizes, annulus diameters, numberof holes, and tube diameters were trialled. A total of eight burners were produced, a summaryof their dimensions is included in Table 10.

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Table 2: Ring Burner Concept Designs

Burner TubeDiameter[inches]

AnnulusDiameter[mm]

Numberof Holes

HoleDiameter[mm]

1 1/4 90 50 1

2 1/4 120 50 1

3 1/4 150 50 1

4 1/4 120 32 1.59

5 1/4 150 32 1.59

6 3/8 120 16 1

7 3/8 150 16 1

8 3/8 120 16 1.59

Figure 20: Auxiliary Burner Concept Design

The hole size was between 1mm and 1/16” (1.59mm). A smaller hole increased the outletvelocity and turbulence of the flow but a larger hole would reduce outlet velocity, presenting arisk of flashback due to the partial premixed operation of the burners. It was unknown how theflames produced by the burners would interact with each other so the amount of holes and theannulus diameter of the burners were varied together to analyse the effect of hole spacing onthe coflow. Furthermore, given an annulus diameter, the variation of hole number also changedthe total outlet area and thus the outlet velocity through each hole. This then affected theturbulence created by the burner. Previous work on this project suggested that two sequentialburners may allow for better control over the temperature and composition of the gases [10],therefore combinations of burners were trialled in addition to the tests of individual burners.The testing results, analysis and final design justification are outlined in Section 7.1.

Final Design and Justification

From the auxiliary burner testing, two 3/8” ring burners 6 and 7 were selected. The downstreamburner, number 8, consisted of 16 1/16” holes in a 120mm annulus and the upstream burner,number 7, contained 16 1mm holes in a 150mm annulus. Both burners were produced using

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3/8” 316 stainless steel tubing with Swagelok R© fittings. The full selection process is detailed inSection 7.1.

Potential Design Issues

Flashback is a common problem in burners operating in premixed mode. To reduce the risk offlashback occurring in the auxiliary burner, partially premixed combustion will be used through-out the data acquisition and appropriate safety measures such as flashback arrestors were used.

Material degradation is another potential design issue associated with the auxiliary burners.The operation of two burners in sequence may cause the downstream burner to experiencehigh-temperature corrosion from the oxidant within the burner in combination with the flametemperatures of the upstream burner. Consequently, the burners were regularly inspected andcleaned. In addition, extra auxiliary burners were manufactured so that burner replacement wasa simple task if a failure eventuated.

5.3.3 Flow Conditioner

The scope of this project is to develop a better understanding of MILD combustion in anenvironment that is representative of a sequential gas turbine. A unique feature of this researchproject is the use of the non-recirculating exhaust gases to facilitate the MILD regime in asecondary combustor. While this is representative of the sequential environment, the shortdistance between the chambers means that inlet flow into the second chamber is dominated byturbulence and non-uniform flow conditions. Laminar coflow conditions are desirable for theexperimental phase of this project as turbulence introduces complexing mixing chemistry and ismore difficult to model. Furthermore, non-uniform temperature and velocity profiles introduceinterpretation difficulties.

The installation of a flow conditioning device was considered to decrease large scale turbulence,temperature and velocity variations in the coflow stream prior to entering the jet exit plane.Installation of a corrective flow conditioner was dependent on the auxiliary burner performance.Being drawn upon in the event that uniformity of the coflow was not adequate for experimen-tally repeatable data acquisition or amenable to 2-dimensional modelling. Despite an extensiveauxiliary burner design and redesign phase, temperature variation was found to be unacceptable,hence an opportunity to improve coflow uniformity remained.

A 304 stainless steel honeycomb flow conditioner originally installed in the combustor apparatusfor the 2013 experimental study [10] The honeycomb section was custom made, with cell widthand diameter defined to meet turbulence damping and flame quenching requirements. Theeffects of the honeycomb can be seen in Figure 21. As is evident by these temperature plots,significant uniformity was achieved through its installation. However, the construction materialwas unable to withstand the temperatures reached in the combustor and therefore failed. Thisweakness was hence a key consideration when formulating the new design criteria.

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(a) Without Honeycomb (b) With Honeycomb

Figure 21: Previous temperature distribution with and without honeycomb

Design Specifications

The specifications were broken down into primary and secondary groupings to assist in evaluatingcommercially available materials. These are presented below:

Primary Requirements

• Reduce turbulence scale

• Reduce velocity and temperature variations

• Dampen disturbances without a significant pressure drop

• Withstand the operating temperatures in the combustor (up to 1623K)

• Product is manufactured to be suitably large

Secondary Requirements

• Easy installation and manufacture, including easy integration with the redesigned centralfuel injector

• Maintain flexibility for removal if the system failes to meet primary design specifications

• Low cost

• Sourced locally

• Used in a similar application

• Not require significant modifications to the current apparatus for installation

Concept Designs

Skewed profiles and unacceptable variation from the auxiliary burner testing motivated an in-vestigation into materials that would withstand high temperatures with the necessary porosity.Consultation with staff at The School of Mechanical Engineering Workshop and vendor com-

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panies supplying high-temperature materials led to the identification of the following feasibleoptions:

• Alumina foam (pressure drop to great and therefore was deemed unsuitable)

• Baked terracotta ceramic with coffee particles (significant time investment for an uncertainoutcome)

• Ceramic aluminium smelting filters

• SIVEX ceramic foam filter (phosphate-bonded alumina based product)

• Ceramic furnace bricks

• Steatite ceramic balls on stainless steel perforated plate

Drawing on the design specifications led to the evaluation of all options and a final materialwas chosen for purchase. The combustor dimensions (200mm ID) eliminated both the ceramicaluminium filters and SIVEX foam filters as both were manufactured to a maximum diameterof 150mm. A steatite ceramic ball system was originally the preferred installation. This sys-tem consisted of one lower perforated stainless steel plate mounted on internally welded tabs.Positioned on the top of the plate was 2-4kg of 4mm diameter steatite ceramic balls. Thisdesign was chosen as it has successfully reduced asymmetry in similar projects, and individualmaterials were expected to withstand combustor operating temperatures. The melting rangeof 316 stainless steel is between 1644 and 1672K and is 2163K for steatite ceramic. Materialavailability, from Dr. Medwell and The Mechanical Workshop also promoted the trial of thissystem. After preliminary testing, the perforated plate distorted under operating temperaturesand the weight of the steatite balls, causing it to slip off the inner tabs. For this reason othermaterials were chosen for further investigation.

Alumina foam and ceramic furnace bricks were options reviewed later in the projects life, withthe ceramic furnace bricks considered to be more cost-effective than the alumina foam. Un-fortunately, a rudimentary evaluation of the bricks demonstrated insufficient flow through thematerial. Alumina foam was considered as it is used as a flame stabiliser in a similar experimen-tal study. The foam product investigated had a sufficiently high melting point to ensure thatstructural integrity was maintained at the temperatures reached in the combustor. Throughmodifications made by The Mechanical Engineering Workshop the foam would rest on the ex-isting tabs inside the combustor. This fabrication along with the rigidity of the material wouldprevent a similar issue that occurred with the steatite conditioning system from reoccurring.Additionally a 20mm hole could be drilled in the centre of the foam to allow the central fuelinjector to pass through the foam. This product was purchased through MTI Corporation, amanufacturer of oxide crystals and substrates in The United States. It arrived for use late inthe year, however the porosity of this product was too low and therefore was never installed inthe combustor. The Concepts were consequently re-evaluated and steatite was selected as aninterim solution for the justification of a flow conditioner in future research.

The reconsidered steatite system consisted of a wider perforated stainless steel plate that couldbe positioned between the top of the auxiliary chamber and manufactured extension piece. Bysecuring the plate between the flanges of the two sections, the problems of plate distortion andslipping was removed. Testing was completed for two trial runs to validate the benefit of aconditioning system, after these test runs the plate failed and could no longer be used. The

36

plate failure can be seen in Figure 22. Consequently a reliable system was not developed withinthe timeframe of this project.

Figure 22: Steatite flow conditioner failure

5.3.4 Extension Tube

An understanding of the coflow stream is fundamental to this research project, as observationsand conclusions regarding the MILD jet flame are to be made based on coflow environmentalchanges. The jet exit plane was determined to be the optimal height for coflow data acquisitionas it best represents the coflow environment reacting with the methane fuel issuing into theprimary section of the combustor. To enable accurate testing within this plane an extensiontube was manufactured and can be seen in Figure 23. During the experimental testing phasethe tube was mounted to the lower auxiliary section, and a perforated plate was secured to thetop for the collection of data at specified radial locations.

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Figure 23: Experimental Testing Extension Tube

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6 Experimental Testing

This section of the report acts to explain both the equipment used and the measurement tech-niques drawn upon to collect relevant and experimentally repeatable data. The testing wasundertaken over an eight-month period at The University of Adelaide’s testing facility, locatedin Thebarton. A combustor apparatus that was design to replicate the conditions experiencedin the second stage of a sequential turbine was used for testing.

6.1 Objective

The MILD regime has been successfully applied in steel and ceramic furnace environments, andits application in gas turbines has been the focus of a number of experimental studies [47, 48,55]. However, for MILD combustion to become integrated in systems with restrictive operatingconditions, a greater understanding of flame stability must be realised. Specifically, how therelationships between parameters such as jet velocity, coflow oxygen content and temperaturefavour or impede the stability of a MILD flame. This project aims to determine the factorsthat effect the stability of the MILD regime, hence determining its suitability in a sequentialturbine. The information to be collected includes species composition, coflow temperature andvelocity profiles, and imagery of the central jet flame for analysis. Relationships between thecoflow environment and the jet flame stability may be determined through the review of videosand OH photos at varying coflow heat inputs, equivalence ratios and jet velocities.

6.2 Methodology

The preliminary testing phase involved commissioning of combustor components followed bythe identification of an approximate range of conditions where a jet flame would evolve. Thiswas achieved by finding a reference point where stable jet and auxiliary flames were maintainedand adjusting input parameters until irregularities appeared. Multiple auxiliary burners andburner combinations were iteratively reviewed to determine the arrangement producing greatestuniformity for future testing.

Initial testing of the coflow temperature uniformity was conducted using a perforated stainlesssteel plate allowing for the visual evaluation of colour contrast indicating temperature variation.Further uniformity verification was carried out by manufacturing and installing an extensionsection (internal diameter 200mm, height 365mm) to enable data acquisition at the jet exitplane, 24 shows the combustor with extension fitted. Given the large coflow diameter comparedto the jet size, it is assumed that entrainment of the surrounding oxygen-rich air will not reducethe accuracy of the results. Velocity, temperature, oxygen and carbon monoxide concentrationwere recorded using a polar coordinate system around the jet and was facilitated by a perforatedstainless steel plate mounted on the extension piece. The plate was cut with 15mm holes at radialintervals of 0mm, 25mm, 45mm, 65mm and 85mm at 45◦angular intervals, as shown in Figure25. In this study, the measurements were taken under varying heat and equivalence ratio inputs.The coflow temperature and species concentration were taken at operating temperature using agas analyser. The velocity measurements were taken using hotwire anemometry however, dueto instrument limitations, were collected at ambient temperature. Consequently, the volumetricflowrate of the fuel was substituted for an equivalent air input.

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Figure 24: Experimental Testing Arangement

Figure 25: Measurement Plate

Following the verification of an ideal burner combination and operating range, an extensive jettesting program was initiated. The jet testing and analysis consisted of observing the flameexposed to a range of coflow environments at laminar, transitional and turbulent exit flows.Multiple images were taken of the flame at each specific coflow environment and jet velocity

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combination. Photographs were taken for analysis of visible reaction zone and images usingan OH* filter were used to view the presence and intensity of this intermediate. The resultsobtained using the extension section were verified by taking measurements at the same locationsand conditions with the original primary section mounted.

6.3 Experimental Setup

6.3.1 Combustor

The MILD combustor apparatus can be broken into three major sections, a diffuser cone throughwhich compressed air enters, an auxiliary section which houses the two ring burners, and aprimary section where the central jet exit plane is located. The height-adjustable central jet(4.55mm ID) is 1450mm long and designed for nonpremixed combustion, an essential componentof this research. The jet is encased by two concentric tubes that allow for water cooling. Theintegration of a cooling system prevents the fuel temperature from rising above 800K that maycause undesirable thermal cracking of the fuel. Fibrous Superwool R©insulation was installed onboth the primary and auxiliary sections (200mm ID) to reduce the heat loss of the system duringoperation.

The auxiliary ring burners were designed to operate in either partially premixed or premixedmode, with the purpose of generating hot, dilute exhaust gases for use in the MILD reactionzone. The two auxiliary burners have been manufactured from 3/8” 316 stainless tubing, andare 140mm apart. The lower ring burner has a diameter of 120mm drilled with 16 x 1mmequispaced holes. The upper burner has a diameter of 150mm and is drilled with 16 x 1.59mmholes. The two ring burners are ignited using a spark plug, located above the lower burner. Theexhaust gases travelling from the auxiliary chamber pass through a flow-conditioner to decreaseturbulence and velocity fluctuations. The hot, diluted exhaust products then travel into theprimary combustion chamber where the central jet exit is located. It is inside this chamber thatthe conditions are conducive for a MILD jet flame. Optical access is possible through a circularopening in the primary section of the combustor, for future pressurisation it has been designedto accommodate a quartz-glass insert.

Both the ring burners and central jet use natural gas as a fuel source and is supplied to theprimary chamber via the central fuel jet and the auxiliary chamber through the ring burners. Theglobal equivalence ratio is modified by altering the air and natural gas flow rates. Consequently,these adjustments change the excess oxygen and heat input into the primary section, varyingthe reaction environment for the jet flame.

6.3.2 Gas Supply

Compressed air and natural gas supplies were necessary for the experimental testing phase. Theair supplied to the auxiliary burners and base diffuser cone was provided by an air compressorand air dryer system, producing 500kPa output pressure. Natural gas was required for boththe nonpremixed central jet flame and partially premixed auxiliary burners. The natural gaswas supplied by Origin Energy through a gas line within the testing facility with a maximumpressure of 100kPa. The approximated chemical composition is summarised in Table 3 wasdetermined for use in similar JHC experiments conducted at The University of Adelaide [10,23],however variations in composition are expected.

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Table 3: Natural Gas Composition at Thebarton

Components Natural Gas Mole %

Nitrogen 0.934

Methane 91.990

Carbon Dioxide 2.560

Ethane 4.280

Propane 0.194

Iso-Butane 0.011

Norm-Butane 0.016

Norm-Pentane 0.004

Hexane Plus 0.008

Total 100

6.3.3 Plumbing

The data analysis process required all input parameters to be independently controlled. There-fore, separate natural gas supplies were needed for the central jet and the auxiliary burners.Similarly, to facilitate premixing in the ring burners, the air supply to the auxiliary section andbase of the combustor was separated into two lines, each regulated by needle valves, pressureregulators and flowmeters. The diagrams in Figure 26 and Figure 27 illustrate the plumbingand instrumentation related to the natural gas, compressed air and cooling water flow paths.Cooling water was supplied into the base of the combustor from the water mains and was con-trolled by a ball valve. It exited in a similar manner and temperature was monitored to ensureadequate cooling.

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Figure 26: Thebarton Piping and Instrument Diagram

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Figure 27: Apparatus Plumbing Arrangement

The air supplies were all plumbed using blue hoses and quick-connect fittings for ease of assemblyand disassembly, similarly, yellow hoses and brass Swagelok R© connections were used for allnatural gas supplies. The colour coding of gas supply lines was in accordance with AustralianStandards. All gas supplies were regulated and measured using needle valves, pressure regulatorsand flowmeters. Flowmeter software from ABB was used to determine the appropriate float andtube pairings for the desired flow conditions, and for the subsequent conversion from percentagemaximum flow rates to equivalent mass and volumetric values. The flowrate sizing recordsgenerated using the software can be found in the testing notes in Appendix D.

6.3.4 Measurement Instrumentation

Testo 350 XL Gas Analyser

Gas composition in the exhaust was measured using a Testo 350 XL portable flue gas anal-yser. The gas analyser uses electrochemical sensor cells for the measurement of O2, CO, NO,NO2 and unburnt hydrocarbons (UHC), and a nondispersive infrared sensor cell for CO2 [56].The exhaust gas is drawn through a sampling probe, a moisture filter and finally to the measure-ment cells. Condensate is separated and particles are filtered from the dry gas before analysisoccurs. The final measurement data displayed is the ratio of pollutant formed to the mass ofthe fuel input.

When reviewing the concentrations determined by the Testo analyser, it was important tonote that the emission levels were reported by volume on a dry-basis, due to the moistureremoval, while GasEq software calculates combustion assuming wet-basis. When consideringthe measurement of excess oxygen, this variation can alter the final value by 1-2% depending

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on the amount of moisture present prior to extraction, as recommended by the manufacturer.

The sampling probe used for exhaust species analysis was equipped with a built-in thermo-couple. Previous work within this project used external thermocouples to collect temperatureprofile data, however as the temperatures reached during testing with the jet exit open to the at-mosphere were not greater than 1500K the Testo measurements were presumed accurate enoughfor the purposes of this study.

Hotwire Anemometer

Measuring low velocities, like those that will be in the primary chamber, is non trivial. Previousresearch used a pitot-static tube, however the resolution is not high enough for the flow condi-tions. Consequently, for further velocity measurements, a VelociCalc R© air velocity meter, model9565 hotwire anemometer was used. Due to the physical sensitivity of the hot wire, the measure-ment environment was limited to room temperature. Therefore, the fuel flow was substitutedwith additional compressed air through the ring burners for the velocity testing phase.

6.3.5 Cameras

A key component of the final analysis involves the interpretation of the central jet flames visualappearance and OH* chemiluminescence. Generic flame behaviour was recorded in movie formatwith a Canon 60D camera via remote capture software and a 15-85mm lens set to 85mm.Photographs of the hydroxyl radical were taken using a pco.PixelFly CCD mounted to a LambertInstruments image intensifier with a 78mm f/3.5 lens (set to f/3.5) and through an Andover310/10nm bandpass filter. The specific settings of both cameras are outlined in the testingnotes in Appendix D.

6.3.6 Errors

Errors pertaining to the measurement equipment, input conditions and general recording inac-curacies are expected to arise in any experimentally oriented study. Measurement equipmentemployed during the testing program can be associated with both inherent equipment inaccu-racies and parallax errors, particularly when considering the pressure and flow indicators. Thepossible inaccuracies in such measurement tools are outlined below in their respectable sections.In addition, consideration must be given to the inaccuracies that develop from unavoidablechanges in input conditions and hence flow rates, such as the thermal expansion of the jet dur-ing operation, gas composition and temperature. Despite this, most of the errors accounted forare unlikely to cause the experimental conditions to deviate to such a degree that general trendsare incorrect.

Testo 350 XL Gas Analyser

The nominal accuracies of the gas analyser, as specified by the manufacturer can be seen belowin Table 4. During the experimental phase, calibration was undertaken before and after testingto minimise unwanted variations in the final data acquired. Gas of known carbon monoxidecomposition was used to verify the repeatability of the operating conditions, with a target read-ing of 491 ppm, and an acceptable variation of ±10ppm. Over the duration of the project themaximum difference was found to be ±5 ppm before each session, while post testing calibration

45

showed a reading between 30-50 ppm below the target CO concentration.

Table 4: Nominal Accuracies For the Gas Analysis Equipment

Species Measurementrange

Accuracy

O2 0-25% ±0.8%

CO 0-2000 ppm2001-1000 ppm

±5%±10%

CO2 0-25% ±3% m.v.+0.44

NO 0-99 ppm ±5 ppm

NO2 0-99.9 ppm ±5 ppm

UHC 100-4000 ppm CH4 less than400 ppm

Hot Wire

As specified by the manufacturer, the accuracy of the velocity measurements from the VelociCalc R©airvelocity metre is 5% of the reading or 0.01m/s, whichever value is greater.

Flowmeters

Flowmeters were a necessary tool for the calculation of compressed air and fuel flows into theauxiliary burners, base diffuser cone and central jet. The flowmeters used were of a tube andfloat arrangement, with pressure gauges attached. At full scale, the inaccuracies as quoted bythe manufacturers are 2% for the flowmeters and 1% for the pressure gauges. Operation at fullscale was desirable, but not always possible given the conditions investigated in this project.For this reason, it is likely that the errors will be greater than the values quoted above. Thedetails of all the tube and floats used are outlined in the Table 5.

Table 5: Natural Gas and Compressed Air Flowmeters

Supply line Flowmeter tube Flowmeter float

Compressed AirBase inletAuxiliary burners

FP-3/4-27-G-10/55FP-1/2-17-G-10/55

FP-3/4-GNSVGT-54FP-1/2/GSVT-44

Natural GasCentral jetAuxiliary burners

FP-1/2-21-GUSVT-410FP-1/2-21-P-10/55

FP-1/2-B372-V07FP-1/2-GUSVT-410

When considering results and the repeatability of experimental testing it is therefore not unreal-istic that flowrates and hence equivalence ratios differ greatly. Therefore, when reviewing Testo350 XL logged measurements against GasEq values, a small variation in flowmeter accuracy canbe expected to change the output parameters significantly.

6.4 Central Jet Testing

6.4.1 Coflow Input Conditions

Understanding the conditions of the coflow exhaust gases generated by the two auxiliary ringburners is fundamental for understanding the stability of the nonpremixed central jet flame. By

46

modifying the heat input and the equivalence ratios in the ring burners, it is possible to seethe impact oxygen concentration, velocity, turbulence and temperature have on the stabilisingand destabilising of the central mild flame. This data acquisition, alongside visual analysis,provides an opportunity to determine the optimal conditions for a MILD flame and the variablesthat strongly influence the regime. The experimental testing was undertaken over a range ofequivalence ratios that were determined by the preliminary analysis of the jet flame stability, asmentioned in Section 6.2. By undertaking a general evaluation of coflow conditions for whicha moderately stable jet flame evolves, flow rates were identified for more in-depth research.The corresponding equivalence ratios and adiabatic flame temperatures were determined usingGasEq Chemical Equilibrium software and supported by hand calculations. The GasEq outputsfor each flow condition may be found in Appendix E and the final coflow conditions for jet flameanalysis are given in Table 6.

Table 6: Central Jet Testing Matrix

φ mfuel

[g/min]mair

[g/min]HeatInput[kW]

Tadiabatic[K]

O2

mol/molRejet

0.53 21.66 698.8 18.1 1536 9.3% 1,000, 5,000,10,000, 15,000

0.6 27.2 775.2 22.7 1665 7.8% 1,000, 5,000,10,000, 15,000

0.65 21.66 567.2 18.1 1758 6.7% 1,000, 5,000,10,000, 15,000

0.65 27.2 712.3 23 1758 6.7% 1,000, 5,000,10,000, 15,000

0.72 21.66 514.4 18.1 1871 5.3% 1,000, 5,000,10,000, 15,000

0.72 27.2 646.0 22.7 1871 5.3% 1,000, 5,000,10,000, 15,000

0.72 32.68 776.2 27.2 1871 5.3% 1,000, 5,000,10,000, 15,000

0.78 27.2 596.3 22.7 1966 4.1% 1,000, 5,000,10,000, 15,000

0.78 32.68 716.4 27.2 1966 4.1% 1,000, 5,000,10,000, 15,000

0.85 32.68 657.4 27.2 2069 2.7% 1,000, 5,000,10,000, 15,000

The above table illustrates input flows calculated using ABB flowmeter software and maximumflame temperatures and O2 mole concentration using GasEq analysis software. In reality, thecoflow temperature can be assumed to be at least 300K less than the adiabatic flame temper-ature due to unavoidable residual radiation losses through the combustor. Additionally, post-combustion comparisons of excess oxygen using instrumentation will differ as GasEq reports wetbasis percentages and the Testo records dry basis. Analysis of the species concentration andtemperature may be collected under normal operating conditions, however the collection of tur-bulence intensity and velocity must be substituted for the compressed air due to instrumentationlimitations.

47

6.4.2 Central Jet Input Conditions

The central jet testing program involved taking observations of the central jet at four differentjet velocities and varying coflow conditions. Four jet Reynolds numbers were chosen to facilitatelaminar, transitional and fully turbulent jet fuel flow to be observed. The mass flowrate and exitvelocity of the jet for an exit temperature of 300K are displayed in Table 7. With the inclusionof the water cooling system, it is assumed that the influence of the coflow temperature will notcause the fuel temperature to greatly deviate from this value despite the unavoidable heatingnear the top, uncooled, segment of the jet.

Table 7: Central Jet Parameters

Fuel Rejet m g/min vexit m/s

CH4 1,0005,00010,00015,000

2.612.324.837

3.9918.938.156.9

6.5 Coflow Testing

The central focus of this research project was to understand how the coflow environment im-pacted the stability of a MILD jet flame. It was therefore necessary to understand how eachinput parameter, such as bulk flow velocity and equivalence ratio, would change the coflow con-ditions, ultimately leading to the construction of clear relationships between input variables andstability. Data was collected in the jet reaction zone to determine the level of uniformity andabsolute coflow values of velocity, turbulence intensity, temperature, excess oxygen and carbonmonoxide. This parametric study was completed over a series of equivalence ratios and heatinputs into the combustor by first adjusting the heat input at a single equivalence ratio followedby the adjustment of equivalence ratios at a given heat input. An auxiliary burner equivalenceratio of φ = 0.72 was maintained for three bulk flow velocities as it was the only value from thepredetermined data allowing for direct comparison between all three heat inputs (18kW, 23kW,27kW). To observe changes in excess oxygen, data was collected again at 18kW input howeverwith φ = 0.60. The exact coflow environments assessed are presented in Table 8. Furthermore,both the redesign of the auxiliary burners and central jet were focused around improving theuniformity of the coflow at the jet exit plane so that data acquired during jet testing could beinterpreted clearly. Hence, these tests were also performed with the purpose of validating thenewly designed and installed components.

Table 8: Coflow Testing Matrix

φ mfuel

[g/min]mair

[g/min]HeatInput[kW]

Tadiabatic[K]

O2

mol/mol

0.6 21.66 617.3 18.1 1665 7.8%

0.72 21.66 514.4 18.1 1871 5.3%

0.72 27.2 646.0 22.7 1871 5.3%

0.72 32.68 776.2 27.2 1871 5.3%

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7 Experimental Results and Analysis

This chapter presents the data acquired during the experimental testing, detailed in Section 6,and the interpretation of these results. The information is divided into the three focal areas: theauxiliary burners, coflow exhaust gases and the central jet. Iterative auxiliary burner testingwas completed first, followed by a paramteric study of the coflow and finally a qualitative andquantitative jet flame analysis program. The parametric study of the coflow consisted of thecollection of excess oxygen, carbon monoxide, temperature and bulk velocity data at the jet exitplane to both validate redesigned components and to observe how each of these input conditionswould alter the jet flame. The basis for the central jet testing was to observe, record and analysethe flame stability by collecting visual and numerical data of the flame at five jet velocities whilemaking adjustments to the oxygen concentration and temperature of the coflow stream. Thiswas facilitated by the collection of movies and OH* chemiluminscence photographs.

7.1 Auxiliary burner testing

A key element of this research project was to improve the uniformity of the exhaust gas coflowthrough the design of the auxiliary burners. Eight auxiliary burners were designed and testedindividually for conclusions to be drawn of the effects of tube and ring diameter, number ofholes, and hole sizing. Following this, combinations of two and three ring burners were reviewedas the single burners trialled could not sustain a flame at the flow rates required for the study.The specifications of the eight trialled ring burners are outlined in Table 10. The tube sizeswere selected due to the pre-existing Swagelok R© fittings welded in the combustor. The burnerdiameters were chosen in combination with the number of holes to determine the effect of distancebetween holes. The hole sizing was based on the exit velocity, a smaller hole would increase exitvelocity thus introducing a risk of blow-off if the flow rates were raised too high however a largerhole diameter could increase the risk of flashback. Despite researching the design criteria of thering burners, no obvious design principle was apparent. Additionally, previous work using CFDcould not be validated when the physical model was tested as subtle variations in manufacturesignificantly affected performance. Consequently, a trial-and-error approach was taken for theburner design testing.

Table 9: Ring Burner Concept Designs

Burner Tube size[inches]

BurnerOD [mm]

Numberof Holes

Hole size[mm]

1 1/4 90 50 1

2 1/4 120 50 1

3 1/4 150 50 1

4 1/4 120 32 1

5 1/4 150 32 1

6 3/8 120 16 1.59

7 3/8 150 16 1

8 3/8 120 16 1.59

Visual observations were used for the preliminary evaluation of the auxiliary burners as generat-ing temperature and species profiles through detailed measurements required a significant timeinvestment which was impractical given the strict timeline and availability of the test facilities.A perforated stainless steel plate was mounted at the jet exit plane so that the temperaturedistribution could be observed by the colour variation in the plate. Figure 28 demonstrates an

49

example of such a test, the brighter areas indicating higher temperature. The auxiliary fuel andair flow rates were altered for each combination so that stable flames were visible from all exitholes of both burners.

Figure 28: Auxiliary Burner Testing

Through this iterative process, the most appropriate burner combinations were determined. Thefinal combination comprised of burners 6 in the upstream location and 7 in the downstream.The use of three ring burners was discontinued due to the difficulty of maintaining stable flamesin all three burners.

7.2 Coflow Testing

The presentation and discussion of results in the proceeding section are related to the operationof the combustor apparatus without the installation of a flow conditioner. Based on their abilityto reduce coflow variability, the auxiliary burners were tested and a final selection was made.The use of a corrective flow conditioner was to be considered if further improvements wererequired. The removal of irregularities in the coflow through burner design was preferable as itwould void the requirement to research and design a flow conditioner to adequately distributeflow variables.

7.2.1 Coflow Velocity

The velocity of the coflow strongly influences the flow field and chemical interactions betweenthe jet fuel and exhaust products. As non-uniformity in the velocity profile would result in askewed MILD flame, an axisymmetric coflow environment was desirable for observations andanalysis, and for quality conclusions to be drawn.

Profiles for the mean axial velocity collected at the jet exit plane using hot-wire anemometryare shown in Figure 29. A peak velocity of 0.54 m/s at y=65 and x=0 are observed for thelowest equivalence ratio of φ=0.60. Comparisons show that the environment at the highesttemperatures (27kW) had the lowest degree of variability. Additionally, all profiles show thepresence of higher velocities in the top left hand quadrants, suggesting the presence of a bias inthe auxiliary burners.

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(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 29: Radial velocity plots at the jet exit plane

Slow reaction rates in the MILD regime increase the influence of molecular diffusion on flamecharacteristics, resulting in modelling difficulties as conventional approaches to combustion mod-elling are suitable to fast chemistry. Major sources of modelling errors result from the approxima-tion of turbulent flow patterns, and often discrepancies between predictions and measurementsexist [57]. Hence, smaller scale turbulence in the jet exit plane was desirable for the collectionof meaningful experimental results, flame interpretation and future modelling. Fluctuations invelocity for each of the coflow conditions can be seen in Figure 30. By reviewing the standarddeviation of the velocity measurements it was possible to to determine the degree of variabilityof the velocity, an indication of turbulence. Similar to the velocity profiles shown in Figure 29,noteworthy variation exists in the upper left hand quadrants.

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(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 30: Radial Standard Deviation Plots at the Jet Exit Plane

The redesign of the central fuel jet, auxiliary burners and installation of the flow conditioner wasmotivated to remove disruptions to the exhaust flow and consequently interpretation difficultiesassociated with modelling. Velocity and standard deviation profiles were therefore also used asa tool to determine whether these objectives had been achieved. Figures 29 and 30 show a clearbias in the upper left quadrant of the velocity and standard deviation profiles. Comparisonsbetween the profiles do not differ greatly, however further Matlab R© analysis on the coflowprofile φ = 0.72 at 27kW heat input found a 0.24m/s difference between the maximum andminimum velocities. Considering a maximum velocity of 0.41m/s for this coflow environment,this difference is undesirable and will likely cause variation in mixing between jet fuel andcoflow reactants. Consequently the central jet flame structure will be inconsistent, introducingdifficulties for the evolution of MILD and analysis.

7.2.2 Coflow Temperature

The MILD regime relies heavily on the reactants being above the fuel’s autoignition temper-ature. Previous research has suggested a strong relationship between coflow temperature andthe stability of a jet flame in a vitiated coflow [47, 55]. Given the sensitivity of self-ignitionand the relationship between temperature and flame stability, a temperature profile symmetricaround the jet is important, particularly in avoiding extinction pockets and inconsistent flame

52

behaviour. Furthermore, temperature uniformity is desirable from a modelling perspective as itallows for a two-stream analysis in future research [47].

Radial temperature measurements were obtained across the range of coflow testing conditionsdetailed in Section 6.5, the profiles can be observed in Figure 31. The peak temperature reachedin the coflow was 895 ◦C at φ=0.72 and a heat input of 27kW. In all coflow conditions, high tem-perature regions are focused between 90 and 270 degrees. As evident by the radial profiles, thepeak temperatures obtained in case b are higher than those in case c. This result is unexpectedas an increased heat input should be accompanied by higher peak temperatures. Evaluation ofthese results led to the hypothesis that similarity between cases a and c and cases b and d waslikely due to the data acquisition method. To reduce testing bias results data was taken in arandom order, this being cases a, c, b and then d. From a physical evaluation of the auxiliaryburners, a build up was found in the upper burner in the section corresponding the upper leftquadrant of the radial profiles. It is possible that an internal build-up developed over the testingperiod, causing a disruption in the gas flow in the auxiliary burners. While the exact cause ofthis is unknown, it is possible that the dual burner configuration caused the lower burner toheat the upper to a point where material degradation was initiated.

(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 31: Radial Temperature Plots at the Jet Exit Plane

Sliced temperature profiles were taken along the 90-270 degree plane (z=0) for additional ob-servations. Despite the aforementioned likelihood of a build up in the burners due to burner

53

degradation, all profiles show low variability on either side of the jet.

(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 32: Sliced Temperature Plots at Exit Plane

The variance of a data set is a measure of spread of the data. Equation 15 was used in theanalysis of the temperature profiles to be used to determine the variance of a vector where µis the average of the data set, N is the length of the data set and Ai represents each individualdata point. A variance of zero indicates that all the numbers are the same. This equation wasused to give a value of the temperature distribution in the coflow at the jet exit plane.

V ar =1

N − 1

N∑i=1

|Ai − µ|2 (15)

Table 10: Temperature Variance

φ Heat Input[kW]

Variance

0.60 23 877

0.72 18 1846

0.72 23 1420

0.72 27 1120

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The variance calculated from the previous groups recorded temperatures ranged between 19,084and 60,471 [10]. Therefore, a significant reduction in temperature variance has been realisedthrough the redesign of auxiliary burners.

7.2.3 Coflow species composition

Species measurements were taken using a Testo R© flue gas analyser and radial profiles weregenerated in MATLAB R©. The species of particular interest were O2 and CO.

Excess Oxygen

A key requirement for the development of the MILD regime is an oxygen parched environ-ment. Like velocity and temperature, axisymmetry was desired for the interpretation of resultsand clear conclusions. Prior to testing, the excess oxygen in the coflow was determined by usingcombustion equilibrium calculations. From these, φ=0.72 was predicted to produce an excessO2 of 5.3% and 7.8% for φ=0.60. Comparisons of these values in Figure 33 show higher actualexcess oxygen, as measured by the Testo R© gas analyser. Given the errors in the flowmeters,pressure gauges, Testo R© analyser and the unavoidable presence of parallax errors these differ-ences are not unexpected. Interestingly, there is a large degree of variation between Figures 33b ,c and d, when the excess oxygen should remain constant given the input conditions. Thisvariation can similarly be explained by burner degradation and the sequence of data acquisition.This bias emphasises the need for flow conditioner and either a regular maintenance schedule orreconsideration of the dual-burner system.

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(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 33: Radial Oxygen Plots at the Jet Exit Plane

Carbon Monoxide

Carbon monoxide measurements were also taken for validation of auxiliary burner performanceand to gain a more detailed understanding of the reactions occurring in the auxiliary chamber.As aforementioned in Section 2.3.1, CO generation is evidence of incomplete combustion. Inter-estingly, profiles a and c show a high degree of uniformity, with CO measurements predominatelyreading as 0 ppm. However profiles b and d indicate higher levels of CO production, a maximumof 120 ppm, in the same quadrant where non uniformities exist in both temperature and velocitymeasurements. This reiterates the possibility of a internal build up that is hindering completecombustion in a portion of the auxiliary burners, and the need for a burner review. What isalso noteworthy is the spike present in the middle of all four profiles. This is presumed to be aresult of thermal boundary layer created by the water flow in the heat exchanger.

56

(a) φ=0.60, Heat Input = 23kW (b) φ=0.72, Heat Input = 18kW

(c) φ=0.72, Heat Input = 23kW (d) φ=0.72, Heat Input = 27kW

Figure 34: Radial Carbon Monoxide Plots at the Jet Exit Plane

7.3 Coflow Testing with Flow Conditioner

Considering the presence of non-uniformity in the coflow stream, research into a flow condi-tioning system was justified. As outlined in Section 5 of this report, materials with sufficientporosity and operating temperatures were considered. While the final system was imperfect,it provided justification for the installation of a flow conditioner. Results were taken with theinstallation of the steatite system and compared to the same operating conditions recorded with-out a conditioning system. A stainless steel perforated plate was installed between the auxiliarysection and extension tube, with 2kg of steatite placed on top, the operating conditions wereadjusted to φ=0.72 and a heat input of 18kW. As expected, the stainless steel plate failed due tohigh-temperature corrosion after a two hour operating period. Figures 35 illustrate the oxygenand temperature of the coflow stream. Carbon monoxide was excluded as the profile could notbe generated due to the measured emissions exceeding the maximum detectable limit. What isevident from these results is improved temperature symmetry about the central jet. Conversely,the temperature variance with steatite in place is 1927 compared to 1846 without, a minor de-cline in uniformity. Furthermore, an increase in oxygen variability was observed. From theseresults, it is clear that the installation of the exact system installed requires refining.

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(a) 18kW (b) 23kW

(c) 27kW

Figure 35: Oxygen and Temperature Profiles with Steatite Flow Conditioning System

7.4 Central Jet Testing

The following section details the visual observations of the central fuel jet at four jet veloc-ity/Reynolds number cases, over a series of coflow conditions. The observations were recordedusing a Canon 60D camera to present CH* radical intensity and a CCD camera with a OH*chemiluminescence filter for OH* intensity. Initially, priority was given to the establishment of aMILD reaction at the jet. Subsequently, a detailed assessment of flame stability was completed.The flame lift-off height, reaction intensity and gradient were the characteristics reviewed in thisexperimental study of the analysis of flame behaviour. Methane was used as the jet and coflowfuel throughout the testing phase.

7.4.1 Key Flame Characteristics

The analysis of the flame structure and its stability was conducted by first altering a parametersuch as jet velocity, coflow temperature or coflow oxygen content followed by the documentationof the jet flame’s behaviour. The flame in each condition was captured using photography andOH* chemiluminscence and the images were compared and evaluated. The characteristics of

58

interest of the flame were its lift-off height, OH* intensity, CH* intensity, and flame reactiongradient.

The flame becomes lifted when the velocity of the fuel is increased beyond the flame speed. Alifted flame is considered unstable as a slight variation in jet velocity can risk flame blow off,a situation where the flame speed can not sufficiently oppose the supply velocity. A desirablecharacteristic of the flame is therefore little to no flame lift-off.

The reaction gradient is of interest in this study as it assists in the definition of the combustionregime. A conventional jet flame can be distinguished by its sharp base and steep reactiongradient, the reaction zone is clearly defined. A flame operating in the MILD regime howeverdisplays a more gradual reaction.

The intensity of both the CH* and OH* in the flame is also of importance in the identificationof a MILD flame. The most obvious attribute of a visible, conventional flame is the presence ofthe CH* radical, giving the flame its distinctive blue colour. It is well documented that the CH*intensity radically drops as it transitions to the MILD combustion regime. Similarly, the presenceof the OH* radical also decreases, however still remains distinguishable in chemiluminescenceimages. The comparison of the intensity levels of both CH* and OH* in the images thereforeaid in the identification of the of flame’s operating region.

The described characteristics can be seen in the set of images in Table 11. The upper flameoperates in the conventional regime and is in a coflow at 940◦C and containing 5.3% excessoxygen. The lower flame operates in the MILD regime, in a 970◦C coflow containing 2.7%excess oxygen. The standard images in the left column show the difference in CH* luminosity,the conventional flame is clearly visible while only a faint outline can be made out of the MILDflame. The MILD reaction however is clearly visible in the chemiluminescence image. Thecolorcube map in MATLAB R© was used to assign contours to the flame, increasing the level ofdetail in the images, thus assisting in the comparison of lift-off heights and reaction gradients ofthe flames, these images are shown in the far right column. Both flames display similar lift-offheights, however the MILD flame shows a notably lower reaction gradient.

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Table 11: Flame Characteristics

CH* OH* Colorcube

Conventional flame

MILD flame

7.4.2 Jet Velocity

Changes to flame behaviour as a result of jet velocity variations were reviewed by increas-ing the flowrate through the jet between laminar and turbulent flows at exit. One lami-nar (Rejet=1,000), one transitional (Rejet=5,000) and two fully turbulent jet flow conditions(Rejet=10,000, Rejet=15,000) were chosen for testing. For the purpose of this study, flame lift-off height was defined as the lowest point at which a reaction could be observed in either thestandard or chemiluminescence images. Lift-off heights were measured and recorded by compar-ing each image against a reference image. The heights were then plotted with their respectiveReynolds numbers for each excess oxygen and temperature at the three tested heat inputs todetermine flame trends.

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(a) 18kW (b) 23kW

(c) 27kW

Figure 36: Flame Lift-Off Height versus Jet Reynolds Number

Lift-Off

A positive correlation between jet Reynolds number and flame lift-off height was evident in allanalysed cases. The lift-off height of a premixed flame is dependent on the flame speed and thevelocity of the unburned mixture entering the flame zone, however a nonpremixed jet is also re-liant on the mixing mechanism combining the fuel and oxidant streams. Increasing temperatureof the reaction accelerates the reaction kinetics, thus producing greater flame speeds resultingin decreased flame lift-off. Therefore, at higher temperatures, the increased reaction kineticsdominates the behaviour of lift-off so the impact of jet velocity reduces. This is evident by thedecreasing reynolds number vs. lift-off slope as heat input is raised.

A similar result has been documented by Ramachandran et al. [48], who found a significantreduction in flame lift-off when heated coflow was substituted in place of an unheated flow.These results are however contradicted by the experimental results reported by Oldenhof [55],shown in Figure 37, who observed that the lift-off height would initially decrease as the outletReynolds number was raised from 3,000 to 5,000. While that observation does not directly alignwith the results found in this experiment, the differences may originate from the smaller stepsize used in the Oldenhof experiments.

The trends displayed in the three plots differ depending on the heat input. A notable occur-

61

rence displayed in all three plots however, is the relatively low variation in flame lift-off betweenReynolds numbers of 10,000 and 15,000. The general downstream trend, as described, is fromthe increasing fuel speed. The decreased effect of fuel velocity at higher Reynolds numbers canbe explained by the transition of the jet exit from laminar to fully turbulent. The dominatingmixing mechanism of the laminar flame is diffusion, therefore a longer ignition delay time existsas the flame can only occur when the fuel and oxidant mix has reached the stoichiometric ratio.The mixing is enhanced when the jet exit flow is fully turbulent, therefore the lift-off height isprimarily dependent on the flame speed and fuel velocity.

Figure 37: Lift-Off Heights vs. Jet Reynolds Number using Dutch Natural Gas in the Delft-in-hot Coflow Burner [55]

Reaction Intensity and Gradient

An increase in CH* intensity can be observed in Figure 38 with increasing jet Reynolds number,particularly in the environment with 5.3% excess oxygen (φ = 0.72) and a heat input of 18kW.Considering this, and the gradual intensity gradient in the correlating OH* images, it wasconcluded that this flame displayed typical characteristics of a MILD flame at Rejet = 1000.However, despite the temperature and excess oxygen conditions being maintained, the flamedeviated from MILD to a conventional regime when the Reynolds number was increased.

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(a) Rejet=1,000 (b) Rejet=5,000 (c) Rejet=10,000 (d) Rejet=15,000

Figure 38: Standard images of jet flames at φ = 0.72 and T = 850◦C (18kW heat input)

(a) Rejet=1,000 (b) Rejet=5,000 (c) Rejet=10,000 (d) Rejet=15,000

Figure 39: Chemiluminescence images of jet flames at φ = 0.72 and T = 850◦C (18kW heatinput), exposure time of 100ms

(a) Rejet=1,000 (b) Rejet=5,000 (c) Rejet=10,000 (d) Rejet=15,000

Figure 40: Standard images of jet flames at φ = 0.72 and T = 870◦C (23kW heat input)

63

(a) Rejet=1,000 (b) Rejet=5,000 (c) Rejet=10,000 (d) Rejet=15,000

Figure 41: Chemiluminescence images of jet flames at φ = 0.72 and T = 870◦C (23kW), exposuretime of 100ms

(a) Rejet=1000 (b) Rejet=5000 (c) Rejet=10000 (d) Re=15000

Figure 42: Standard images of jet flames at φ = 0.72 and T= 940◦C (27kW heat input)

(a) Rejet=1000 (b) Rejet=5000 (c) 10000 (d) Rejet=15000

Figure 43: Chemiluminescence images of jet flames at φ = 0.72 and T= 940◦C (27kW), exposuretime of 150 ms

7.4.3 Temperature

The temperature of the coflow environment had the most significant effect on the flame char-acteristics, an increased coflow temperature produced a lower lift-off and an overall decrease inOH* intensity and reaction gradient. The temperature of the coflow stream was altered via twomechanisms, the bulk flow velocity and the oxygen content. The bulk flow velocity could beraised by increasing all flowrates into the system, this would maintain a constant equivalenceratio but increase the temperature at the exit plane of the combustor. Alternatively, the flowrateof air into the system could be lowered, shifting the reaction toward stoichiometry and reducing

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the cooling effect of the air, also resulting in an increased temperature. Both cases were howevercoupled to their respective inputs. If the temperature was increased through the bulk flow veloc-ity mechanism, the flame’s behaviour could also be affected by the increased velocity. Similarly,a temperature change through the alteration of excess oxygen could produce a compound effecton the flame. These effects can be decoupled by substituting pure nitrogen gas in conjunc-tion with the air in the system to independently control the excess oxygen at a given velocity.This method has been used in previous studies however was not practicable within this research.

Flame Lift-Off Height

The lift-off behaviour observed in this section stems from the effect of temperature on the flamechemistry. Increasing the temperature of the flame’s environment effectively reduces the ignitiondelay time in the jet’s reaction zone, resulting in decreased lift-off heights. A similar effect hasalso been documented in both the Ramachandran and Cabra studies [47, 48]. This behaviourcan be observed in Figure 45, where the lift-off height is lowered from 132mm (T=808◦C) to47mm(T=870◦C) and then to 20mm (940◦C).

Reaction Intensity and Gradient

A clear difference in species intensity can be observed when comparing the standard and OH*images. The standard images show similar CH* intensities at all three operating conditions,however a clear positive trend s evident in the OH* images, showing that a greater number ofintermediate reactions are occurring. This effect can be explained by the dependency of OH*formation rate on temperature, as the OH* radical requires high activation energy in it’s for-mation, an increase in temperature facilitates its production. This observation is agreeable withfindings from similar studies [24].

(a) 18kW ,T= 808 ◦C (b) 23kW ,T= 870 ◦C (c) 27kW ,T= 940 ◦C

Figure 44: Standard photographs of central jet flame at φ=0.72, Rejet=5000, O2 = 5.3%

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(a) 18kW ,T= 808◦C (b) 23kW, T=870 ◦C (c) 27kW, T=940 ◦C

Figure 45: OH* photographs of central jet flame at φ=0.72, Rejet=5000, O2 = 5.3%, 100msexposure time

7.4.4 Oxygen

Oxygen is fundamental for the oxidation of hydrocarbons. Changes to jet flame behaviour withalterations to the available coflow oxygen is a focus of this study. While it is known that theMILD regime evolves at low oxygen conditions, the specific operating window and the specificflame chemistry at varying oxygen contents still lacks understanding. Diagnostic techniquesemployed for flame analysis rely on photon emissions from the decaying hydroxyl radical, in theform of OH* chemiluminescence images. The formation of OH is a key intermediate reaction inhydrocarbon combustion, where 80% of the available oxygen is used. Consequently, the oxygencontent in the coflow stream impacts flame behaviour and OH* chemiluminescence can be usedto identify the flame front. Visual and numerical analysis of the central jet flame were taken oversix equivalence ratios, depicting six variations in coflow excess oxygen ( φ = 0.53−O2 = 9.3%,φ = 0.60 − O2 = 7.8%, φ = 0.65 − O2 = 6.7%, φ = 0.72 − O2 = 5.3%, φ = 0.78 − O2 = 4.1%,φ = 0.85 − O2 = 2.7%). Noteworthy from the data is the impact oxygen has on OH* intensityand lift-off height.

As aforementioned, decoupling the effects of oxygen from temperature was not within the scopeof this study due to financial and time restrictions. Consequently, interpretations made on theeffects of oxygen must be considered alongside the effects of temperature.

Flame Lift-Off Height

Similar work on jet in hot coflow flames have found a clear shift of the flame base downstreamas excess oxygen in the coflow decreases. At the lower heat inputs it is clear that a reductionin oxygen content causes an increase in lift off height. This is to be expected as under highlyoxygen parched conditions the formation of a homogeneous reaction zone takes longer, leadingto the large downstream shift in the position of ignition kernel formation. Over each of the fourjet velocities and coflow temperatures reviewed, the same conclusion could not be drawn fromthis study. Images presented in Appendix F demonstrate a reduction in lift-off height variabilityas the oxygen content in the coflow is decreased. However as the full range of oxygen conditionsfrom 2.7% to 9.3% were reviewed over varying coflow heat inputs, and the temperature was un-able to be decoupled from changes in oxygen concentration it is not possible to draw conclusions.Additionally, results highlighted previously demonstrate the increased stability through increas-ing temperature, it is likely that the coflow temperature has a greater effect on the lift-off heightvariability reduction rather than the decreasing oxygen contributing to the lift-off behaviour

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Reaction Intensity and Gradient

The flame behaviour as excess oxygen is decreased at constant coflow temperature and jetvelocity (Rejet = 5, 000) can be observed in Figures 46 and 47. The first two cases display theexistence of a conventional flame, visible in both the standard and OH* images. However thethird case (φ= 0.85), shows minimal luminosity in the standard image despite a clearly definedflame in the OH* image, a distinctive characteristic of a MILD flame. Additionally, decreas-ing oxygen levels in the coflow results in the suppression of the hydroxyl radical, evident bythe decrease in intensity in Figure 47c. This observation can be attributed to two influencingmechanisms,reduced temperatures in the MILD reaction zone and less available oxygen for thereaction with hydrogen for the OH production. As discussed in section 2.3.2, the productionof the OH* radical requires high activation energy and thus occurs primarily at higher tem-peratures, therefore a reduced temperature and reduced available oxygen content produce acompound effect of lowering the formation of the hydroxyl radical.

(a) 5.3%, T = 940◦C (b) 4.1%, T = 950◦C (c) 2.7%, T = 970◦C

Figure 46: Standard photographs at Re=5000 and 27kW

(a) 5.3%, T = 940◦C (b) 4.1%, T = 950◦C (c) 2.7%, T = 970◦C

Figure 47: OH* photographs at Rejet = 5000 and 27kW, 100ms exposure time

7.4.5 MILD combustion

The aim of this continuation project was to create conditions in the combustor apparatus thatwere appropriate for the development of a MILD jet flame. Previous work on this project failedto produce MILD combustion. By redesigning components that limited the evolution of MILDand data acquisition, an improved experimental apparatus was developed.Testing over a seriesof coflow conditions yielded a MILD jet flame at three locations, this was validated through anabrupt drop in CH* and OH* intensity. The MILD flames and their respective environmentsare presented in Table 12.

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Table 12: MILD Jet Flames

No. O2[%] Temp. [◦C] Re Standard OH*

1 6.9 795 1,000

2 6.1 940 1,000

3 2.9 970 1,000

4 2.9 970 5,000

5 2.9 970 10,000

6 2.9 970 15,000

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A classic example of a MILD flame was established at 2.9% oxygen and 970◦C for all jetReynolds numbers (1,000-15,000), the lowest oxygen and highest temperature coflow environ-ment. At higher excess oxygen levels, between 6% and 7%, the images showed a reduction inCH* and OH* intensity for laminar jet velocities, cases 1 and 2. These characteristics indicatethat a MILD flame may have evolved, however as MILD was not displayed at all jet Reynoldsnumbers, it is not certain at these conditions.

Cases 1 and 2 in Table 12 present a higher CH* intensity with increasing fuel velocity,indicating a deviation from the MILD regime to a more conventional flame. This change canbe observed in Appendix F. A possible explanation for this phenomenon is related to reactantentrainment. With increasing jet velocity, the turbulence of the jet flow is also increased,therefore entraining more of the coflow reactants from a larger radius resulting in a widerreaction zone. Hence, if the properties of the coflow are vary with radius, the composition ofreactants mixing with the jet fuel will change as the reaction zone increases. Figure 48 showsthe increase in oxygen concentration with increasing radius for case 2. Originally, it was thoughtthat the increase in available oxygen was insignificant, however a similar parametric studyundertaken by Ramachandran et al. found a transition from conventional jet flame at 7.39%oxygen to flameless at 7.37% [48]. Considering this, it is plausible that the small differencesobserved in the coflow stream may cause the jet flame to deviate from MILD to conventionalcombustion with the increased reactant entrainment. Validation of this will require furthertesting near these conditions, and improvements to the uniformity of the coflow.

Figure 48: Mean oxygen content vs. radius for case 2

7.5 Conclusions

The experimental research undertaken was broken into three areas, auxiliary burner performancetesting, exhaust gas coflow testing and a qualitative analysis of the central jet flame. Throughthis testing phase an improved coflow environment was realised and a greater understandingof the mechanisms of greatest impact on flame stability were identified. Through the use of aparametric coflow study on four coflow environments, the benefits of the chosen burner designand configuration were validated. Compared to previously designed auxiliary burner systems,

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the temperature variance was significantly reduced. Furthermore, it was shown that though theinstallation of a flow condition, further improvements could be realised, pertaining to improvedaxisymmetry.

The central jet testing phase involved a qualitative and quantitate review of a jet flamein a vitiated coflow environment that was modified to observe the effects of oxygen andtemperature. Additionally, modifications to the central jet fuel velocity from laminar to fullyturbulent conditions helped observe stabilising mechanisms. The most significant outcomeof this testing phase was the evolution of MILD combustion, which had not previously beenachieved in this apparatus. Noteworthy from the flame analysis was the major impact of coflowtemperature on lift-off height reduction. This result is concurent with similar research and is animportant step to understanding the most important controlling mechanism practical systemshave to ensure successful and stable integration of MILD combustion.

The limitations pertaining to the decoupling of temperature on oxygen restricted thedepth of conclusions. Consequently, future work would benefit from integrating nitrogeninjection systems similar to other test apparatus systems. Furthermore, a more detailedanalysis is required around the region where MILD combustion developed to better understandthe transition from a jet flame in a vitiated coflow to a MILD flame. As flame speed is also akey contributor to lift-off and it is known that flame speed changes under pressure, the resultsdiscussed in this section will require reassessment under pressurised conditions.

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8 Design of Future Components

For future quality results to be realised, testing under pressurised continues is fundamental.Additionally, experimental data collected on the coflow profiles necessitates the redesign of theauxiliary burner system and a flow conditioning device. This section presents the preliminarydesign calculations for a pressure vessel, the redesign of the auxiliary burners and introducesconcept designs for the flow conditioner.

8.1 Preliminary Design of Pressurised Combustor

The second stage of a sequential gas turbine operates above atmospheric temperature and pres-sure. Research has been conducted into the stability of the flame at various temperature, velocityand oxygen content, however these tests were conducted at atmospheric pressure. As little isknown about the suitability of MILD combustion under elevated pressures, this design will al-low fundamental research to be undertaken pertaining to the stability of the flame in conditionsexperienced within a sequential turbine. The self-ignition of various fossil fuels becomes easierat elevated pressures and as this is a requirement for the MILD regime, understanding how thiswill affect stability is crucial [24]. Further, testing under pressurised conditions is also impor-tant as ignition delay and flame speed are reduced at higher pressures, highlighting that MILDcombustion will behave differently at elevated pressures [3]. The current apparatus will not holdinternal pressure at the operating temperatures because the stainless steel is heated to a pointwhere the structural integrity is compromised, thus a more suitable design solution is required.

8.1.1 Design Specifications

1. Accommodate a maximum allowable working pressure of 5 bar, as this is similar to theconditions experienced in the second stage of a sequential gas turbine

2. Maintain structural integrity at the maximum operating temperature of 340 K (at theinterior of the pressure vessel)

3. Provide easy access to the combustor for external and internal maintenance4. Include sealed air and gas inlet points for all gas supply lines (2 premixed air/fuel streams

for the ring burners, 4 compressed air inlets into the diffuser cone and one natural gasinlet at the base)

5. Provide optical access that is in line with the current combustor quartz glass window forvisual analysis of the jet flame

6. Include a point of access for measurement instrumentation in the jet exit plane7. Accommodate a pressure relief valve on the upper horizontal surface

8.1.2 Design Alternatives

The pressurised chamber could have been designed in various ways. The main objective was tobuild a combustion chamber that could withstand 5 bar of internal pressure, at temperaturesaround 100◦C, and at a reasonable cost. Considering the melting point for stainless steel wasnot significantly higher than that reached within the combustor, designs were investigated formaintaining structural integrity and safety at elevated temperatures.

Cooling fins could be placed on the outside of the combustor, reducing temperature andtherefore increasing the strength of the stainless steel. This was the simplest solution howeverdecreasing the temperature of the chamber would change the internal temperature profile,consequently affecting the velocity and carbon monoxide profiles.

Ceramic insulation could be placed on the inside of the combustor, reducing the heattransfer coefficient through to the stainless steel. This would require ceramic tiles to be bonded

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to the stainless surface on the inside of the combustor, reducing the overall diameter of thecoflow and introducing other implications for analysis.

Alternatively, other materials, such as tungsten or titanium, could be used for a com-plete rebuild of the combustor, however the manufacturing required for this would be complexand expensive.

Lastly, the construction of a pressure vessel around the existing combustor was investi-gated. This would allow the existing combustor to take the thermal load while the externalcylinder takes the pressure load. As obtaining the appropriate conditions for MILD combustionin the existing combustor was nontrivial and significant resources investments into this designhave been made, this was considered the most feasible option.

8.1.3 Final Design

The selected design for future pressurisation consisted of the construction of an external pressurevessel to encase the combustor. This design includes 50mm of superwool ceramic fibre insulationand allows for a 15mm air gap for heat dissipation. A schematic of this design can be seen inFigure 49.

Figure 49: Schematic of Pressure Vessel Design

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8.1.4 Material Selection

Australian standards 1210 for pressure vessels were consulted to ensure compliance and integrityof the design [58]. For material suitability and safety an approved pressure vessel material wasdesirable, thus PT430 carbon manganese steel was selected [59]. It is acknowledge that thematerial is rated to higher pressures than required, however it was the minimum as specifiedby the standards and will allow for future testing at pressures greater than 5bar. Standardthickness PT430 grade steel is desirable to reduce costs and lead-time, these range from 5mmto 100mm.

8.1.5 Design calculations

The initiation of design calculations was an extension objective of this project. As mentionedabove PT430 grade pressure vessel steel was selected due to its guaranteed performance atpressure. Calculations from AS1210 were used to determine the minimum thickness for thepressure vessel given the design conditions. Following this, heat transfer calculations were usedto validate that the temperature experienced by the pressure vessel was suitable for the selectedmaterial thickness. The tensile strength of the selected material reduces as temperature increases(shown in Appendix H) thus, verifying the temperate at the pressure vessel was important. Thematerial properties used are presented in Table 13 and detailed calculations are in Appendix G.

Table 13: Material properties used for heat transfer calculations

Properties 316 StainlessSteel

PT430 Steel SuperwoolInsulation

Thermal Conductiv-ity (W/m.K)

15.2 56.7 0.44

Inner Radius (mm) 100 168 103

Thickness (mm) 3 tmin 50

Minimum wall thickness

AS1210 were used to calculate the minimum wall thickness for the pressure vessel underthe design conditions. The tensile strength of the material were taken at 50◦C (see AppendixH for PT430 properties), an approximate for the conditions at the inner wall of the pressurevessel. The minimum thickness based on the longitudinal and circumferential stresses werecalculated to be 0.45mm and 0.23mm respectively. As the minimum thickness of PT430 gradesteel was 5mm this thickness was selected.

Maximum operating temperature

To determine the temperature at the inner surface of the pressure vessel wall as describedin the concept design, a one dimensional steady state analysis was completed. This analysisassumed that temperature gradients existed along only a single coordinate and the heat transferoccurs exclusively in this direction. In true operating conditions a one dimensional steady stateanalysis would be inexact as vertical temperature variations would vary greatly from the baseto the top due to the location of the burners and the effects of buoyancy. However, calculatingbased on the maximum known coflow temperature is sufficient as it captures the worst casescenario. The heat transfer modes considered are:

• Conduction through the combustor wall and insulation• Convection and radiation through the pressurised air• Conduction through the pressure vessel

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With appropriate boundary conditions defined, the temperature distribution can be solved bydrawing on the concept of thermal resistance and an analogy between the diffusion of heat andelectrical charge, this is shown in Figure 50.

Figure 50: Heat transfer through pressurised combustor

The final calculations were completed with the following assumptions:• The convection coefficient of air, hair is 5 W/m◦C• The highest temperature reached internally in the combustor is 1500K

From these calculations the maximum temperature of the inner wall of the pressure vesselwas 70◦C. The thickness calculations were based off a tensile strength at 50◦C, however thetensile strength of PT430 remains the same up to 100◦C, validating that 5mm PT430 steel wasappropriate.

8.1.6 Future Considerations

As these calculations were intended as a preliminary design the following factors should beconsidered prior to implementation of the design;• The loss of thickness due to scaling [58]• Confirm temperature at the external insulation and the distance of the pressure vessel via

physical measurements• Ensure temperatures do not exceed 425◦C - at temperatures above this graphitisation and

embrittlement of PT430 steel occurs [58]• Hazard assessment, as required by the Australian pressure vessel standards• Complete drawings of pressure vessel• Consultation with pressure vessel specialist

By measuring the temperature of the external insulation the accuracy of the calculations may bedetermined and hence the design recommendations provided. Furthermore, it would be beneficialto measure the temperature of a metal sample at the design distance from the insulation tovalidate that reduced temperature assumptions are plausible.

8.2 Future Auxiliary Burner Design

The modified auxiliary burners produced a suitably uniform coflow and sufficient heat tofacilitate testing to improve understanding of the stability of MILD combustion. However, theuse of two auxiliary burners introduced material degradation issues in the upper burner dueto the constant heat exposure. The degradation resulted in blocked outlet holes leading tocoflow uniformity problems. Although fabrication and testing of a new burner was outside ofthe scope of the project, it was advantageous to redesign the auxiliary burners for future use inthe combustor.

The primary objective of the new design was to use a single auxiliary burner, to prevent

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the rapid degradation of the upper device. To ensure that sufficient heat could be deliveredfrom the single burner, calculation were undertaken to ensure that the total outlet hole area ofthis design was the same as the previous design.

h = nπd2

4+ n

πd2

4

h = nπ12

4+ n

π1.592

4= 44.30mm2

nπd2

4= 44.30mm2

Try d=1.59mm, n = 22 holesWhere:h is the total hole arean is the number of holesd is the hole diameter

From these calculation it was determined that a hole size of 1.59mm with 22 holes would providesufficient heat and is suitable for manufacture. As 316 stainless steel was appropriate for theprevious lower burner and is readily available, it will be used for this component. The fittingsin the combustor are 3/8” so to prevent further modifications 3/8” stainless steel tubing willbe used. An outer diameter of 135mm was selected, as it is between the previous burner sizes,so should provide sufficient radial temperature distribution to evenly heat the coflow. The finaldrawings of the design is pictured in Appendix C.

8.3 Future Flow Conditioner Concept Designs

Due to problems with the flow conditioner design, concept designs were generated for imple-mentation in the future of this project. The intention of the flow conditioner is to improveuniformity of the coflow and dissipate turbulence. Concept designs include;• Custom-drilled plate of high-temperature alloy• Custom-cut high temperature ceramic• Fine 3D printed Mesh, from a high-temperature alloy such as Titanium

Dissipation of turbulence is related to mesh sizing, therefore the printed mesh is the most ap-propriate concept. However, the suitability of this manufacturing method and feasible materialsrequires further research.

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9 Conclusions

A focus on efficiency improvements and emission abatement is pivotal for the future of energygeneration given fossil fuel scarcity, climate change and population growth. Unfortunately, theseobjectives are currently contradictory. Gas turbine applications require higher temperaturesfor the extraction of thermal energy, however NOx production increases exponentially aboveapproximately 1500◦C. Through research and development, a promising combustion regimehas been identified that is capable of meeting both objectives. MILD is a unique combustionprocess that evolves when reactants are above the auto-ignition temperature of the fuel andhave a low oxygen concentration. These features induce longer chemical reaction time scalesand consequently a distributed reaction zone. What originates from this is a greater degreeof transferrable heat and a reduction in peak temperatures, hence both a higher thermalperformance and a reduction in NOx emissions is an obtainable goal. For gas turbine applica-tions, further benefits exist including the elimination of thermo-acoustic instabilities and, whileabove the auto-ignition temperature, the risk of flame extinction. Furthermore, application insequential gas turbines shows promise as the environment created in the secondary combustionis similar to the required operational environment for MILD.

At present, no known commercially viable sequential gas turbine operates the MILDcombustion regime due to uncertainties. This positioning results from an incomplete under-standing specifically pertaining to the operating conditions necessary to achieve MILD, thetransition region from conventional combustion to MILD and the origins of instabilities. Tohelp reduce these gaps in understanding, studies that can experimentally recreate the operatingenvironment in sequential gas turbines are fundamental. Previous work on this project involvedthe design and build of a model gas turbine combustor, however, MILD combustion did notevolve and the complexity of data interpretation was increased due to inconsistencies in flowconditions. This motivated the redesign of problematic components, comprising of the primaryfuel injector, auxiliary burners and flow conditioner.

Non uniformity in the coflow and fuel decomposition occurred as a result of the originaljets entry point, compromising results and modelling. Research was undertaken into similarjets to ascertain existing designs and methods for fuel temperature control. From this, a con-centric tube heat exchanger jet was designed that entered through the base of the combustor.This design met the specifications for the fuel delivery system, allowing adjustability andsignificantly reducing disruptions to the coflow. Furthermore, the functionality of the heat ex-changer was confirmed as the cooling fluid remained at room temperature throughout operation.

The requirement to improve uniformity of exhaust coflow from the auxiliary burners wasidentified via visual analysis during preliminary testing. In theory, the original burners shouldhave produced a more evenly distributed flow, however in reality, inconsistencies related tofabrication made the asymmetry unavoidable. Furthermore, research was conducted into thedesign of burners however no exemplar design could be established. It was therefore determinedthat an iterative trial-and-error approach must be used for the selection of the final burnerswith varying outer diameter, number of holes and hole size. A qualitative study was used todetermine the most suitable design. Visual analysis was undertaken using a stainless steelplate to observe temperature gradients for different burners and burner combinations. Thetesting phase saw the selection of two burners that produced the most acceptable profiles witha lower total temperature variation than other combinations. Further investigation into coflowprofiles found a maximum recorded temperature variation was 20.57%, exceeding the initialtemperature variation of 12.43% in the same burner combination. The deteriorating uniformityof the coflow suggested burner degradation, hence a new design was completed for fabricationand testing in the future.

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The flow conditioner required redesign as it had been produced from a thin, stainlesssteel honeycomb and was damaged in the high-temperature environment. Consequently, itcould not be used in the preliminary testing phase, reiterating the importance of a new, robustconditioning system. The flow conditioner was a corrective mechanism used to decrease largescale turbulence, temperature and velocity variations in the coflow stream prior to entering thejet exit plane. Inclusion of such a device was considered dependent on the auxiliary burnerperformance, in that it would not be required if adequate uniformity was achieved. Preliminaryresults from the extensive auxiliary burner redesign suggested that coflow was sufficientlyuniform to operate without a conditioner. However, the rapid deterioration of the burnersproduced temperature differences greater than the acceptable variation, hence an opportunityto improve coflow uniformity remained.

An investigation into flow conditioning materials was motivated by skewed profiles andunacceptable variation resulting from the degradation of the auxiliary burners. Such a materialneeded to withstand high temperatures and contain the necessary porosity to prevent asignificant pressure drop in the coflow. Several feasible materials were identified, and at thecompletion of the data acquisition phase steatite ceramic balls on a perforated stainless steelplate was tested due to the availability of the steatite. This conditioning system showed positiveeffects, significantly improving the uniformity of the coflow. However, the high temperaturescaused the stainless steel plate to fail and thus for this system to be installed an alternatematerial is required to hold the steatite. Following this a rudimentary evaluation of ceramicbricks and alumina foam demonstrated insufficient flow through the materials, producing anundesirably large pressure drop in the coflow. From the improved uniformity from coflowtesting with steatite the installation of a flow conditioner is desirable and hence a new systemprovides scope for future work.

The first stage of data acquisition for the project involved a parametric study of theauxiliary burner exhaust gas coflow at the jet flame reaction plane. Throughout this testingadjustments to the bulk coflow velocity, excess oxygen and temperature were made to observechanges in the jet exit plane and validate redesigned components. Temperature, speciesconcentration (CO, O2, CO2), mean velocity and velocity fluctuation profiles were collected forcomparisons. Uniform temperature profiles of the coflow were critical in the MILD regime dueto its dependence on reactants being above auto-ignition. Further a symmetric profile aroundthe jet is important due to the relationship between temperature and flame stability. Lowoxygen environments are one of the characteristics of a MILD regime and CO concentrationsare an indicator of the burner performance as they indicate incomplete combustion. Small scaleturbulence in the jet plane was desirable for collected meaningful results and ultimately improv-ing understanding of MILD combustion, hence velocity profiles and fluctuations were important.

From these profiles, a clear bias was visible with nonuniformities present in the same re-gion for the CO, temperature and velocity profiles, reiterating aforementioned problems withthe deteriorating condition of the auxiliary burners. Further, excess oxygen concentrationmeasurements taken for the testo device were higher than calculated suggesting errors withflow meters, pressure gauges, the testo and parallax errors. Of the varying input parametersthe conditions defined by phi=0.72 and a heat input of 18kW showed the lowest degree ofirregularities and expectedly showed the most significant results in later stages of testing,highlighting the importance of coflow uniformity throughout testing of the MILD regime. Hencethe implementation of the new auxiliary burner design or flow conditioning system providedscope for future testing under more desirable conditions.

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A qualitative visual analysis of the central jet flame was undertaken at varying coflowconditions and four jet velocity cases spanning from laminar (Re = 1,000) through to turbulent(15,000). Conditions were varied to determine the conditions where MILD combustion wasachieved, characteristics of the transition between MILD and conventional combustion andmechanisms that affect MILD stability. A MILD combustion flame is characterised by a gradualreaction zone, reduction in CH* intensity and reduced but distinguishable OH* radical. Thusconventional photographs and OH* chemiluminescence images were collected for each set ofconditions so the transition to MILD could be observed. Lift-Off height and the reaction zoneintensity gradient were evaluated and drawn from to better understand jet flames in a vitiatedcoflow stream, and MILD flames.

Coflow temperature and jet Reynolds were shown through standard and OH* chemilu-minescence photographs to have the greatest impact on lift-off height. Temperature wasshown to have a greatest effect on flame characteristics, through decreasing lift-off height, OH*intensity and reaction gradient. While a clear trend relating oxygen to flame stability wasuncertain, although this could be related to testing limitations related to parameter decoupling.

A MILD jet flame was established at 2.9% oxygen, 970◦C for laminar and turbulent jetvelocities. This development validated that the redesigned componentry was successful, andthrough further refining more detailed results will be possible. Due jet velocity limitations,higher Reynolds number were not achievable and hence it could not be concluded whetherthe flame would transition away from MILD above Rejet=15,000. Two other coflow and jetenvironments appeared to create the necessary conditions for MILD combustion. However,interpretation pertaining to mixing chemistry was outside of the scope of this project.

The project was approached in a sequential manner, with the design and fabrication ofthe existing apparatus completed before the data acquisition phase. Throughout the testinginput parameters were varied to extract experimental information into the conditions necessaryto achieve a stable MILD combustion reaction. Relationships between these input conditionswere drawn during the analysis of the data, allowing this gap in knowledge to be narrowed.The extension phase was commenced with design calculations for the pressurised combustioncompleted, allowing a future study into how the MILD regime operates under these conditions.To ensure both the design and data collection/analysis phases were successfully completed, anin depth management strategy was developed to achieve its goals, outlined in Appendix A.

Through the completion of this honours work, an experimental apparatus was refinedthat was capable of creating the necessary conditions for MILD combustion. From this arrange-ment, preliminary analysis on flame stability was completed which will act as the foundationfor future research and be comparable for testing performed under pressure. Fundamentalpressurisation design work was also completed, in addition to the redesign of componentry forfurther improvements in the future.

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10 Future Work

Work completed within the timeframe of this project included the design and manufacture ofcomponentry, experimental testing and preliminary design work for the pressurisation of thecombustor apparatus. Through the completion of the primary and extension objectives, areasrequiring greater focus were identified. For improved data acquisition and results applicable topractical applications, improvements to coflow uniformity, testing focused on the MILD flamesthat evolved and testing under pressurised conditions will be required.

For future experimental research the first area that requires addressing is the auxiliaryburner manufacture, installation and validation. In Section 8.2 a new burner design wasdeveloped with the objective of avoiding degradation and the skewed coflow that results. Byinstalling one larger burner capable of meeting the same flow rates and hence heat input asthe dual configuration it is predicted that the burner degradation will not occur. Manufactureand validation will involve communicating the design drawings to The Mechanical Workshopand using the Testo R©gas analyser to generate a radial profile of temperature, CO and O2 forcomparison with the dual burner configuration.

Despite the design and manufacture of a new burner, it is still recommended that a flowconditioner is developed and tested. While the flow conditioner was intended for installationin the scenario that designed burners could not produce adequate uniformity, over the year itbecame increasingly evident that small unavoidable manufacturing discrepancies caused largeflow alterations. The improved axisymmetry with the installation of the stainless steel steatiteflow conditioner system prompted research into a similar design. Several concept designs weregenerated and are outlined in Section 8.3. Future work includes further research and finalisationof these designs.

Preliminary discussions encouraged the investigation of a similar concept, with the stain-less steel plate substituted for a thicker custom made version or titanium. Iterations todetermine the height of the steatite mass are recommended, as it was hypothesised that theheight prevented flow and caused incomplete combustion in the auxiliary burners.

By improving the combustor apparatus a conducive environment for MILD combustionwas developed, this was validated through the evolution of a MILD flame at three conditions.However, the eventual requirement for practical application necessitates an operating windowand a better understanding of how MILD transitions from conventional combustion. Conse-quently, future work encompasses jet flame analysis at conditions closer to those where MILDwas known to develop in the combustor arrangement. With this focused experimental researchit is hoped that a regime diagram may be formulated for the apparatus.

Analysis under pressurised conditions is necessary as flame behaviour is expected tochange and practical applications require combustion to operate as such. Preliminary pressurevessel design work was completed, including material selection and heat transfer and wallthickness calculations. These calculations were intended as an introductory design and so futureconsiderations, outlined in Section 8.1.6 should be completed prior to fabrication and testing.

Once the preliminary calculations have been validated, future work will entail the pro-duction of design drawings, manufacture, installation and commissioning of the pressure vessel.Subsequent experimental testing similar to that performed in this research project will berequired for comparison.

Through the completion of these future objectives it will be possible for a more detailed

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understanding of MILD combustion to be realised. This understanding increasing the likelihoodthat this unique combustion regime, its environmental and financial benefits may be realised insequential gas turbines.

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[2] Chen, S., Dally, B., Li, P., Liu, Z., Mi, J., Wang, F., Wang, L., and Zheng, C., “Progressand recent trend in MILD combustion,” Science China Technological Sciences, Vol. 54,No. 2, 2011, pp. 255–269.

[3] Turns, S., An Introduction to Combustion: Concepts and Applications, McGraw-Hill Pub-lishing Company Limited, 2000.

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83

Appendix A Management

To facilitate the investigation of MILD combustion in the original test apparatus, design andexperimental objectives required completion. To ensure all objectives were met successfully andto provide a clear timeline of tasks, a work breakdown structure (WBS) and Gantt chart weredeveloped with the commencement of this project. Changes or delays to the goals are discussed inthis section, along with the necessary justification. Risk assessments were completed, including aproject risk assessment, a safety risk assessment, and various safety operating procedures (SOP).These documents have been provided for reference and any failures have been discussed. Finallya breakdown of the budget and resource allocation for the project have been included.

A.1 Work Breakdown Structure

The final WBS for the project is outlined below and follows with a discussion of the changes madeto each subsection. To provide clarity, any additional items in the WBS have been underlinedand items that were omitted have been italicised.1. Research

1.1. Combustion1.2. MILD Combustion1.3. Gas Turbines1.4. MILD Combustion in Furnaces1.5. MILD Combustion in Gas Turbines1.6. Prior Work in The Field1.7. Primary and Auxiliary Burner

1.7.1. Commercial Product Benchmarking1.7.2. Materials

1.8. Flow Straightening Device1.9. Flames Analysis1.10. Pressurised Combustor

2. Design2.1. Review of Existing Design2.2. Risk Assessment2.3. Specifications

2.3.1. Identifiaction of Operating Conditions2.3.2. Sizing

2.4. System Design2.4.1. Primary Burner2.4.2. Auxiliary Burner2.4.3. Connection Device2.4.4. Extension Tube

2.5. CAD Model2.5.1. Decide on Software2.5.2. Assembly Model

2.5.2.1. Sub-Assembly Models2.5.2.1.1. Individual Part and Fasteners

2.5.3. Generate and Dimension Drawings2.5.4. Bill of Materials

2.6. Commissioning2.6.1. Primary Burner2.6.2. Auxiliary Burner2.6.3. Flow Conditioner

84

2.6.4. Primary Burner2.6.4.1. Omitted - Internal Flow Distribution Analysis2.6.4.2. Omitted - External Flow Distribution Analysis

2.7. Pressurisation2.7.1. Design Specifications2.7.2. Design Details

3. Manufacture and Construction3.1. Job Hazard Analysis (Risk Assessment)3.2. Primary Burner3.3. Auxiliary Burner3.4. Burner Assembly3.5. Fit Assembly to Test Apparatus

4. Testing4.1. Determination of Auxiliary Burner Configuration4.2. Ideal Auxiliary Burner Flow Rates4.3. Commissioning of Steatite Flow Conditioner4.4. Primary Burner Flame Analysis4.5. Range of Conditions Primary Burner Operates Within4.6. Chemiluminesence Imaging4.7. Flame Photographs/Movies4.8. Coflow Velocity4.9. Coflow Composition and Temperature4.10. Verification of Results with Top on Combustor4.11. Commissioning of Alumina Foam Flow Conditioner

4.11.1. Coflow Velocity4.11.2. Coflow Composition and Temperature

4.12. Omitted - Verify Results4.13. Omitted - Evaluate Results

5. Analysis of Results5.1. Coflow Composition/Equivalence Ratio Calculations5.2. O2 Profiles5.3. Temperature Profiles5.4. Velocity Profiles5.5. Conversion of Movies to Screenshots5.6. Interpretation of Chemiluminesence Images5.7. Flame Interpretation & Analysis

6. Deliverables6.1. Project Charter

6.1.1. Summary6.1.2. Project Introduction6.1.3. Stakeholders6.1.4. Goals6.1.5. Resources6.1.6. Budget6.1.7. Gantt Chart and WBS6.1.8. Risk Assessment6.1.9. Editing and Submission

85

6.2. Preliminary Report6.2.1. Abstract6.2.2. Introduction6.2.3. Literature Review6.2.4. Gantt Chart and WBS6.2.5. Design6.2.6. Manufacture and Assembly6.2.7. Commissioning6.2.8. Conclusion6.2.9. References6.2.10. Appendices6.2.11. Editing and Submission

6.3. Final Report6.3.1. Abstract6.3.2. Introduction6.3.3. Background6.3.4. Aims6.3.5. Combustor Design6.3.6. Experimental Testing6.3.7. Experimental Results & Analysis6.3.8. Preliminary Design of Pressuriation6.3.9. Engineering Outcomes6.3.10. Management6.3.11. Conclusion6.3.12. References6.3.13. Appendices6.3.14. Editing and Submission

6.4. Mech Expo6.4.1. Abstract6.4.2. Posters6.4.3. Movie of Testing

7. Management and Procedure7.1. Library Workshop7.2. Thebarton Workshop Induction7.3. Technical Mentor Meeting7.4. PDR Meeting7.5. CDR Meeting

ResearchAn investigation into similar research was completed to guide the formation of an experimentaltesting methodology and the redesign of testing apparatus componentry. A review of priorwork was also used to highlight those areas requiring significant focus for the overall outcomeof an increased knowledge-base of MILD combustion. This review of previous work also helpedguide the experimental phase of this project as it provided an insight into successful methodsfor data acquisition. In addition, the research into other jet-in-hot coflow burners guided themodifications to the central fuel jet and flow conditioners.Once the experimental testing phase was completed, further research was necessary for the in-terpretation of features and trends discovered.In particular, once CH and OH* photographs hadbeen collected, a clear understanding for flame analysis was necessary to confirm the establish-ment of MILD combustion and to draw conclusions on flame stability. Furthermore, increasedunderstanding assisted in identifying similarities between this project and other investigations

86

into MILD combustion.Pressurisation of the combustor was an extension goal. Consequently, research into designrequirements was not included in the original breakdown of tasks. Upon completion of theexperimental testing aims, preliminary calculations were performed to generate an initial design.Research into the Australian Standards for pressurised vessel was also necessary for designcompliance.DesignAn extension tube was designed so the conditions could be measured at the jet exit plane. Asthe coflow varied significantly between the auxiliary burners and the central fuel jet exit plane, itwas desirable to record the conditions at the jet exit. As the viewing pane in the combustor wasrestrictive, an extension tube was required to collect temperature, oxygen and carbon dioxideprofiles.The analysis section in the original WBS was replaced with a commissioning section. Theanalysis of the auxiliary burners was a more significant part of the project than originallyplanned due to the iterative design selection process. This commissioning section related toensuring that the components integrated with the existing combustor and that could functionas per their design specifications.A pressurisation section was retrospectively added to the design section once this extension targetwas commenced. This involved determining design specifications, calculations and drawings ofthe proposed pressurisation design.TestingThis section of the WBS received a complete overhaul after an improved understanding of theexact testing were gained. This part was particularly challenging to determine at the early stagesof the project when little understanding of MILD combustion or flame analysis was known. Onceresearch was undertaken into methods of flame analysis this section was reworked and brokeninto specific tests that needed to be carried out. Additionally verify and evaluate results sectionswere removed from the testing and analysis section and into a new section, namely analysis ofresults. This was done as the analysis of results section was determined to be a significant partof this experimentally focused project.DeliverablesThe only changes made to the deliverables section in the retrospective WBS was to the finalreport breakdown. At the commencement of the project it was unsure exactly which sectionsthe final report would contain and so it was always expected that this would be changed once abetter understanding of the project and the marking scheme were gained.

A.2 Gantt Chart

The tasks outlined on the Gantt chart were extracted directly from the WBS and thus theoutlined changes to the WBS were reflected in the Gantt chart. For this reason only the changesin timelines will be discussed. A traffic light system has been used to highlight the effectivecompletion of tasks. Green signifies items that were completed on or before the deadline, redfor tasks that were completed after the deadline and orange was used to new tasks that werenot included in the original deadline.

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3/15 4/15 5/15 6/15 7/15 8/15 9/15 10/15

1830 - Gas Turbine Reheat C... start end

Periods of Unavaliability 11/04/15 04/07/15

April Holidays 11/04 20/04

SEM 1 SWOT VAC 20/06 04/07

Research 09/03/15 30/09/15

Combustion 09/03 06/04

MILD Combustion 09/03 06/04

Gas Turbines 09/03 06/04

MILD Combustion in Furances 09/03 06/04

MILD Combustion in Gas Turbines 09/03 06/04

Prior Work on This Project 09/03 26/08

Primary & Auxiliary Burner 18/03/15 01/04/15

Previous Burner Benchmarking 18/03 01/04

Flow Straightening Device Research 18/03 01/04

Analysing Flames 30/08 14/09

Pressurised Combustor Research 09/09 30/09

Design 12/03/15 02/10/15

Review of Existing Design 16/03 20/03

PDR 01/04 01/04

PDR 10/04 10/04

CDR 08/04 08/04

Drawing Submission Deadline 27/04 27/04

Risk Assessment 27/04 27/04

Specification 27/04/15 27/04/15

Identify Operating Conditions 27/04 27/04

Sizing 27/04 27/04

System Design 27/04/15 27/04/15

Primary Burner 27/04 27/04

Connection Design 27/04 27/04

CAD Model 12/03/15 27/04/15

Decide on CAD Software 12/03 19/03

Assembly Model 27/04/15 27/04/15

Sub-Assembly Model 27/04/15 27/04/15

Individual Part & Fastener Mo... 27/04 27/04

Bill of Materials 27/04 27/04

Generate & Dimension Drawings 27/04 27/04

Commissioning 15/07/15 29/07/15

Auxiliary & Primary Burner 15/07/15 29/07/15

Primary Burner 15/07 29/07

Auxiliary Burner 15/07 29/07

Flow Conditioner 15/07 29/07

Primary Burner 15/07 29/07

Pressurising Design Calulations 14/09/15 02/10/15

Concept Designs 14/09 02/10

CAD of Final Design 14/09 02/10

FEA of Design 14/09 02/10

Manufacture & Construct 15/05/15 15/06/15

Job Hazard Analysis (Risk Assessm... 15/05 20/05

Manufacture Primary Burner 15/05 10/06

Manufacture Auxiliary Burner 01/06 05/06

Construct Burner Assembly 05/06 05/06

Fit Assembly to Test Apparatus 05/06 15/06

Testing 01/07/15 14/09/15

Ideal Aux Burner flow rates 01/07 30/07

Co-Flow Composition & Temperatur... 30/07 14/08

Primary Burner Flame Analysis 14/08 21/08

Range of Conditions that Primary B... 28/08 28/08

Chemi-Luminesence Imaging 04/09 04/09

Flame Photographs/Movies 04/09 04/09

Co-Flow velocity under specified fl... 07/09 07/09

Co-Flow Composition and Tempera... 07/09 09/09

Verification of Results With Top on ... 14/09 14/09

Comissioning of Steatite Flow Condi... 31/07 21/08

Analysis of Results 30/07/15 18/09/15

Co-flow Composition/Equivalence R... 30/07 09/09

O2 Profiles 30/07 09/09

Temperature Profiles 30/07 09/09

Velocity Profiles 07/09 09/09

Conversion of Movies to Screenshots 04/09 10/09

Interpretation of Chemiluminesence... 04/09 18/09

Deliverables 04/03/15 26/10/15

Project Charter 04/03/15 27/03/15

Summary 04/03 13/03

Project Introduction 04/03 13/03

Stakeholders 04/03 13/03

Goals 04/03 13/03

Resources 04/03 13/03

Budget 04/03 13/03

Gantt Chart & WBS 11/03 13/03

Risk Assessment 04/03 13/03

First Draft 06/03 06/03

Editing & Submission 06/03 13/03

Second Draft 13/03 13/03

Submission Deadline 27/03 27/03

Preliminary Report 09/03/15 05/06/15

Abstract 06/04 15/05

Introduction 24/03/15 24/04/15

Motivation/Backgroud 24/03 24/04

Goals/objectives 24/03 08/04

Literature Review 09/03 06/04

Project Management 20/03/15 31/03/15

Team Structure 20/03 23/03

Teamworking protocols 20/03 23/03

Gantt Chart & WBS 23/03 31/03

Design 20/03/15 22/05/15

Benchmarking (fuel inlet, conne... 20/03 17/04

Concept Design (fuel inlet, con... 17/04 24/04

Final Design Details (fuel inlet, ... 27/04 22/05

Manufacture & Assembly 15/05 25/05

Commissioning 25/05 29/05

References 09/03 15/05

Appendices 09/03 15/05

Editing & Submission 24/04 01/06

First Draft 27/04 27/04

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3/15 4/15 5/15 6/15 7/15 8/15 9/15 10/15

Second Draft 15/05 15/05

Submission Deadline 05/06 05/06

Final Report 09/03/15 23/10/15

Review of Prelim Report 30/07 04/08

Abstract 30/07 07/08

Introduction 30/07 07/08

Literature Review & Background 09/03 10/08

AIms 30/07 13/08

Overall Gas Turbine Combustor D... 07/08 21/08

Experimental Testing 01/09 25/09

Experimental Results & Analysis 01/09 25/09

Preliminary Design of Pressurised... 01/09 25/09

Engineering Outcomes 01/09 25/09

Management 01/09 25/09

Conclusion 01/09 25/09

References 01/09 02/10

Appendices 01/09 02/10

First Draft 21/08 21/08

Second Draft 18/09 18/09

Third Draft 02/10 02/10

Submission Deadline 23/10 23/10

Mech Expo 22/07/15 26/10/15

Abstract 22/07/15 04/08/15

First Draft Abstract 22/07 29/07

Second Draft 29/07 04/08

Poster 11/09/15 07/10/15

First Draft Poster 11/09 02/10

Final Poster 25/09 07/10

Mech Expo 26/10 26/10

Management & Procedure 05/03/15 06/05/15

Library Workshop 05/03 05/03

Thebarton Workshop Induction 16/03 16/03

Technical Mentor Meeting 30/03 01/04

PDR Meeting 30/03 01/04

CDR Meeting 06/05 06/05

Learn LaTex 06/03 09/03

Familiarise With CAD Software 13/03 20/03

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Alexander Schumacher, Fiona Lake, Helen Hobbs

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DesignThe specifications subsection was delayed from the original timeline as preliminary testing wascarried out to determine the requirements for the modifications. This process was more cum-bersome than original planned as changes had been made to the original design and so keydimensions needed to be confirmed prior to commencing the design of any modifications.Manufacture and ConstructThe manufacture and construct component of the project was delayed by the mechanical en-gineering workshop. Originally fabrication was estimated to take four full days, however dueto overloading of the workshop it took three weeks for fabrication to be completed. This delayhad little effect on project progress as this time was used to undergo preliminary testing of theoriginal auxiliary burners.TestingAnother part of the project that was not completed to the original schedule was the commission-ing of the flow condition system. As the modified auxiliary burners produced a suitably uniformcoflow, a conditioner was no longer necessary as a corrective device. Once the data acquisitiontesting was completed, a flow conditioning system was trialed to see if it improved the profileuniformity.DeliverablesOriginally the literature review for the final report was only scheduled over a two week period.Once data analysis commenced it was realized that further research was required to analyseand draw conclusions and comparisons from the results. Thus the literature review process wasextended to facilitate on-going research.Another component of the final report that was not completed to the original schedule was theexperimental results and analysis section. In the early stages of the project it was difficult topredict how long this process would take so two weeks were scheduled. However the manipula-tion of the data was nontrivial and involved writing Matlab scripts to time-average the moviesand chemi-luminescence images collected during testing. Additionally to strengthen the resultsconclusions were drawn between the data collected and prior work undertaken in the field.

A.3 Project Risk Assessment

The gas turbine combustor investigation has numerous stakeholders and spanned a significanttime frame. For stakeholder assurance, a risk assessment was essential to ensure threats wereidentified and either eliminated or minimised. The project risk assessment is focused on therisk that the project will fail, rather than a safety risk assessment which will follow. The tablebelow contains a complete list of all conceivable risks to the project, and the actions requiredfor mitigation. For each risk, a risk level was identified from the risk matrix according tothe likelihood and consequence of the threat. A new risk level was then allocated given themitigation actions. By allocating the new risk level the group was able to prioritise mitigationactivities and remain confident that milestones may be met. An analysis of the failure thatoccurred during this project follows.Despite methods undertaken to mitigate any project risks from occurring workshop delays didoccur as outlined in section 1.2. Fortunately these delays did not affect the progress of theproject as other tasks could be completed whilst waiting for the designs to be completed.

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96

A.4 Risk and Safety Assessments

A risk assessment and SOPs were completed prior to commencement of testing. The mainhazards associated with this project were related to the high temperatures (greater than 1600K)experienced in the combustor and exposure to fire hazards. A health and safety risk assessmentwas created to outline hazards and the methods used to mitigate these risks and can be found inappendix AA. Following this an SOP produced to outline the keys steps in ensuring safe start-upof the combustor, as many of the issues were related to the first steps of operation (appendixAAA). A subsequent SOP was completed for the installation and removal of the ceramic fiberinsulation (appendix AAA).Safety Failures Failures occurred during start-up of the combustor and were made especiallychallenging by the restricted visibility of the burners. Thermo-acoustic instabilities were occur-ring in the auxiliary burners under specific conditions. These caused the burner to momentarilyignite before extinguishing. This caused safety risks as if the burners were not alight the com-bustor would fill with methane gas introducing a risk of explosion. The difficulties associatedwith the start-up of the combustor were identified during the preliminary testing and hence theSOP was refined to allow safe operation of the combustor. The mitigation strategies includeddetermining suitable air and gas flow rates for start-up and ensuring that face shields were wornby any persons within close proximity to the combustor. Additionally a mirror was used todetermine if the burners were alight so appropriate action could be taken.Throughout testing the temperature of the cooling water was closely monitored to ensure thatthe fuel was maintained sufficiently cool and that the cooling water did not change states. Atone point it was noticed that the central fuel injector was red hot, and the temperature of thecooling water was elevated. The combustor was turned off immediately and the cooling systemwas inspected. A blockage in the inlet valve of the water pipe was found preventing sufficientwater flow for cooling. A replacement valve was fitted to the water hose and once the central jethad cooled testing recommenced. To prevent this failure from reoccurring, valves were inspectedprior to connection and the water temperature was more closely monitored. Further, the waterflow rate through the cooling system was increased to assist with cooling and prevent damagesto the central fuel injector and decomposition of the fuel.Uniformity problems with the auxiliary burners were noticed during the later stages of testing.The coflow from the burners was noticed to be significantly non-uniform, highlighting thatthere was a problem with the burners. The combustor was turned off to allow inspection ofthe auxiliary burners, and blockages were noticed due to material degradation of the stainlesssteel at the high temperatures experienced in the combustor. Damage to the upper burnerwas worse than the lower burner due to the direct heat experienced. Due to time restraintsthe auxiliary burners could not be redesigned to mitigate this failure completely, however apreventative maintenance strategy was developed. This included a regular cleaning programand the fabrication of spare auxiliary burners. The cleaning included filing the outlet holes toremove blockages followed by passing high pressure compressed air through the burner to checkfor pressure drops. Once the condition of the burners was too bad for cleaning the burners werereplaced.

A.5 Cost Analysis

As outlined in the preliminary report the original project budget was $600 plus any additionalfunding received at the discretion of the supervisor. Table 1 summarises the cost of each compo-nent obtained for this project. As summarised in Table 2 the total procurement for this projecttotalled $1517.3, of this total funding $30 came out of the student budget with the remaining$1487.3 coming from Paul Medwells Research Fund and the Mechanical Engineering Workshop.

97

Table 1: Project Procurement and Funding Source

Component Material Quantity Cost ($)

Funding Source

Supplier

Primary Jet ¼” 316 SS

Tube 1.5m 80 Paul Medwell Excess Supply from

previous work ½” 316 SS

Tube 1.5m 80 Paul Medwell

¾” 316 SS

Tube 1.5m 80 Paul Medwell

SwageLok 3 200 Paul Medwell Excess Supply from previous projects

Auxiliary Burners

¼” 316 SS

Tube 3m 160 Paul Medwell Excess Supply from

previous projects 3/8” 316

SS Tube 3m 160 Paul Medwell Excess Supply from

previous projects Swagelok

T-piece ¾”

1 111.3 Paul Medwell Fluid System Technology

Swagelok Needle Valve

2 26 Paul Medwell Fluid System Technology

1mm Cobalt Drill Bits

10 30 Self-Funded Bunnings Warehouse

Extension Tube

316 SS Tube 200mm OD

500mm 250 Paul Medwell Excess Supply from previous projects

SS plate 2 x 200mm OD

160 Mechanical Engineering Workshop

Mechanical Engineering Workshop

Perforated Plates

316 SS perforated plate 200mm OD

6 Plates 180 Mechanical Engineering Workshop

Mechanical Engineering Workshop

Procurement Total

1517.3

Table 2: Breakdown of Funding Sources

Funding Source Amount ($) Paul Medwell Research Fund 1147.3 Mechanical Engineering Workshop

340

Student Budget 30 Total Procurement 1517.3

A.6 Workshop and Resource Analysis

Part of the University funding for the final year project is a total of 40 hours of workshoptime per student, equating to a total of 120 hours. At the completed design review meetingthe workshop estimated that four full days (32 hours) would be required for fabrication. Thisoriginal estimate did not include the manufacture of the extension tube, the auxiliary burnerconcept designs or the fabrication of the flow conditioner and thus more time fabrication timewas spent on this project. Despite going beyond the original estimation the number of workshophours used in this project was 70 hours, well below the allocated time. The total workshop andresource breakdown is summarised in table 3 below.

A.7 Lessons Learnt

Submission of drawings to the Mechanical Engineering Workshop in a timely manner was criticalto ensure that the fabrication was completed in the early stages of the year. This was achievedin this project as drawings were submitted a month before the deadline. Despite the earlysubmission delays were still encountered, as sufficient time was allowed for such delays this hadno effect on the progress of the project. The early submission was particularly important forthis project as experimental testing on the prototype was the focus of the project.Time management was critical during testing at the Thebarton facility, due to the finite spaceand the large number of groups undertaking testing. Set-up and pack-down of the apparatuswas time consuming leading to a further reduction in testing window. Additionally, beforeany measurement could be taken the combustion needed to reach steady-state further slowingthe testing progress. In the early stages of testing time management was poor so preparationsessions were undertaken prior to testing to plan what had to be achieved. This includeddeveloping spreadsheets that outlined the conditions that needed to be tested and providedspace to record results. Additionally, only two people were required to undertake the testing,giving an additional group member the opportunity to work on other aspects of the project.The unpredicted nature of testing made experimental planning challenging throughout theproject. The auxiliary burner testing took significantly longer than originally planned as eachtest combination had to reach steady state before its performance could be determined. Todetermine the most suitable combination of burners a large number required trialling and hencethis process was more demanding than planned. Further, problems with material degradationin the auxiliary burners meant that a cleaning strategy was implemented and some of the coflowprofiles needed to be retested. As each profile took up to 30 minutes to test this process waslengthy.Another lessons learnt from this project is the time consuming nature of preparing data foranalysis. The main form of data acquisition in this project was the collection of conventional and

99

OH* photographs. Prior to any analysis, this data needed to be time-averaged. This averagingwas carried out using Matlab and was nontrivial due to the lack of experience in reading imagesinto this software. Following this the averaged photographs were manually cropped againstreference images and lift-off heights were recorded. In hindsight it may have been beneficial toinclude code to automatically crop these images in the time averaging script to save time andensure there was no discrepancies between the sizing of figures.The subjective nature of visual observations introduced some issues when determining the lift-offheight from the conventional and OH* photographs. Ideally the measurements would be takenby one person to reduce discrepancies however, the large quantity of images and the restrictivetime frame made this impossible. In future work measurements from photographs should betaken via a Matlab script to eliminate the subjectiveness of visual measurements.A Gantt Chart was developed for the project to keep track of tasks, deadlines and to assigntasks to group members. It was found that the Gannt chart was not necessarily the best wayto keep on track of smaller tasks. A note system was used where a list of the tasks that neededto be completed each week was extracted from the Gantt chart so that the large items couldbe broken down into smaller tasks. This made the project seem less daunting as tasks could becompleted each day.

100

Appendix B Central Jet Design Calculations

%Project 1830: Primary Fuel Injector Design Calculations

%Adapted from D. Bay et al, 2013

clear all

close all

%For sufficient mixing of fuel and coflow stream the Reynolds number must

%be sufficiently turbulent with Re ~10,000

Re = 10000;

P=20E3; %from previous report (can run at least 20kW at Thebarton using natural gas)

LHV=47.141E6; %lower heating value for natural gas

rho_m = 0.667151; %Density of Methane at 300K

mu_m = 1.1E-5; %Dynamic viscosity of Methane at 300K

Q_estimate = P/LHV/rho_m;

Q_Lmin = Q_estimate*1000*60;

D_m = 4*rho_m*Q_estimate/(pi*Re*mu_m); %Minimum Diameter of Fuel Injector

v_m=Q_estimate/(pi/4*D_m^2);

D_chamber = 0.200; %actual chamber diameter

Q_coflow = 0.5865;

V_coflow = Q_coflow/(pi/4*D_chamber^2);

101

S=0.102;

theta = atan(S);

theta_deg=theta*180/pi;

L=(D_chamber/2)/S*0.5;

fprintf(’The maximum inside pipe diameter is %f mm\n’,D_m*1000)

The maximum inside pipe diameter is 4.910759 mm

102

103

Ap

pen

dix

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ngin

eeri

ng

Dra

win

gs

SECTIO

N B-B

SCALE 2: 1

B B

1 1

2 2

3 3

4 4

5 5

6 6

AA

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7/04/2015

DESIG

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1 of 1

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TITLE

AI - 02

Connection Plate

TH

IR

D AN

GLE PR

OJECTIO

N

PR

OJECT

1830: G

as Turbine R

eheat Com

bustor

SCALE

MASS

DO

N

OT SCALE

DIM

EN

SIO

NS IN

MILIM

ETER

S

DR

AW

IN

G STAN

DARD

AS1100

MATER

IAL

QTY

0.137 kg

DR

AW

N

Helen H

obbs

DATE

DATE

DATE

H. H

obbs

A. Schum

acher

6/04/2015

7/04/2015

2:1

Stainless Steel

1

UN

LESS STATED

O

TH

ER

WISE

GEN

ERAL TO

LERAN

CE:

LIN

EAR

:

AN

GU

LAR:

0.3

1

REM

OVE BU

RRS &

SH

ARP ED

GES

ALL O

VER.

3.2

NO

TES.

1. ALL W

ELD

IN

G TO

CO

MPLY W

ITH

AS/N

ZS 1554.1-2004 - STRU

CTU

RAL STEEL W

ELD

IN

G -

W

ELD

IN

G O

F STEEL STRU

CTU

RES.

2. VISU

AL IN

SPECTIO

N O

F W

ELD

O

NLY.

4x

6.5

6.8

TH

RU

EQ

UISPACED

40 PCD

65

19.5

2 X 45

104

PARTS LIST

QTYDESCRIPTIONPART NUMBERITEM

1M6 boltsM6X201

13/4" diameter 3.2mm thick o-ringOR - 3/42

1Air Injector FlangeAI - 01 3

4Connection PlateAI - 024

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

7/04/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

AI - ASM

Air Inlet Assembly

THIRD ANGLE PROJECTION

PROJECT

1830 - Mild Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

2.957 kg

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

F. Lake

6/04/2015

7/04/2015

1:1 1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 - STRUCTURAL STEEL WELDING -

WELDING OF STEEL STRUCTURES.

2. VISUAL INSPECTION OF WELD ONLY.

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

3

2

4

1

PARTS LIST

QTYDESCRIPTIONPART NUMBERITEM

1Swagelok Union Tee 1/2inSS-810-31

1Swagelok Union Tee 3/4inSS-1210-32

1Inner TubeFI-013

1Middle TubeFI-024

1Outer TubeFI-035

1Reducer FI-046

13/4" to 1/2" ReducerFI-057

11/2" to 1/4" ReducerFI-068

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

7/04/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

0

1 of 2

PART NUMBER

TITLE

FI-ASM

Fuel Inlet Assembly

THIRD ANGLE PROJECTION

PROJECT

1830 - Mild Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

F. Lake

6/04/2015

7/04/2015

1:2 1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. MACHINE IN CONJUNCTION WITH FI-04

2. WELD 3/4" AND 1/2" REDUCERS AFTER THEIR RESPECTIVE SWAGELOK

TEE PIECES HAVE BEEN FITTED.

8 1 7 2 3 4 5 6

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

inner_tube

Inner Tube

THIRD ANGLE PROJECTION

PROJECT

1830: Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

H. Hobbs

25/03/2015

8/04/2015

-

Stainless Steel1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. MANUFACTURE FROM 1/4" STAINLESS STEEL TUBING

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

1450

160

1200 6x WELD GROUPS EQUISPACED

( 6.35)

3 EQUISPACED

TACK WELDS

MACHINED TO

10.2

FACE

1.6

SECTION C-C

SCALE 3 : 1

C

C

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

8/04/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

FI-05

3/4" to 1/2" reducer

THIRD ANGLE PROJECTION

PROJECT

1830: Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

0.038 kg

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

F. Lake

8/04/2015

8/04/2015

3:1Stainless Steel1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 - STRUCTURAL STEEL WELDING -

WELDING OF STEEL STRUCTURES.

2. VISUAL INSPECTION OF WELD ONLY.

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

30

19

12.7

SECTION B-B

SCALE 3 : 1

B

B

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

8/04/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

FI-06

1/2" to 1/4" Spacer

THIRD ANGLE PROJECTION

PROJECT

1830: Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

0.023 kg

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

F. Lake

8/04/2015

8/04/2015

3:1Stainless Steel1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 - STRUCTURAL STEEL WELDING -

WELDING OF STEEL STRUCTURES.

2. VISUAL INSPECTION OF WELD ONLY.

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

30

12.7

6.4

SECTION C-C

SCALE 4 : 1

C

C

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

reducer_D2

Reducer

THIRD ANGLE PROJECTION

PROJECT

1830 - Mild Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

A. Schumacher

DATE

DATE

DATE

A. Schumacher

F. Lake

6/04/2015

6/04/2015

4:1Stainless Steel

1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 - STRUCTURAL STEEL WELDING -

WELDING OF STEEL STRUCTURES.

2. VISUAL INSPECTION OF WELD ONLY.

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

NOTE 1:

Machine in conjunction with FI-ASM

1.5

3

19.1

16.6

6.4

R10

7.5

1 X 45 2 POSN

(51.2)

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

24/09/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

AB01

Future Auxiliary Burner

THIRD ANGLE PROJECTION

PROJECT

1830 Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

a1211714

DATE

DATE

DATE

Helen Hobbs

A Schumacher

A Schumacher

20/10/2015

24/09/2015

24/09/2015

1:2

Generic

2

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES:

3/8" Stainless Steel 316 Tube Bent into circle

Holes Drilled After Bending

135 PCD

22 x 1.59mm Equispaced Holes 3mm Depth

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

24/09/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

AB02

Future Auxiliary Burner Connnection

THIRD ANGLE PROJECTION

PROJECT

1830 Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

a1211714

DATE

DATE

DATE

Helen Hobbs

A Schumacher

A Schumacher

20/10/2015

24/09/2015

24/09/2015

1:2

Generic

2

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES:

3/8" Stainless Steel 316

Cut with Water Cutter

32.50

3/8"

PARTS LIST

QTYPART NUMBERITEM

1Connector1

1Ring Burner2

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

24/09/2015

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

AB03

Future Auxiliary Burner Assembly

THIRD ANGLE PROJECTION

PROJECT

1830 Gas Turbine Reheat Combustor

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

a1211714

DATE

DATE

DATE

Helen Hobbs

A Schumacher

A Schumacher

20/10/2015

24/09/2015

24/09/2015

1:2

2

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR:

ANGULAR:

0.3

1

REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES:

Weld connector to ring burner using TIG welding

Ensure smooth inner and outter surface

Weld connection tube to Auxiliary Burner

2

1

Appendix D Testing Notes

114

15/06/2015 Thebarton testing- Running 50 hole ring burners with Paul AIR: Pressure (20kPa), run at 80% Natural gas: Pressure(100kPa), run at 100% (104 g/min)

- 0.305 - CD, constant density glass - Gas @ 95kPa 20% (35.2 g/min) - Air @ 200kPa below 7% (65 g/min) - Can use either CA, SS, TA - Tantalum flow (TA) (FP-1/2-25-TA) - Air @ 300kPa – 18% (60g/min)

Better - gas @ 95kPa 10% (17.6g/min) - air @ 100kPa 6% (11.6 g/min)

Turned burner upside down and increased the air and fuel

- considered the best most uniform flame from using the stainless steel plate for visual analysis

- gas @ 95kPa 10% (17.6g.min) - air @100kPa >25 > 60g/min

For pascal to make up, need 16 holes on each. Need 3/8th current size (120) and ¼ larger size (150).

-

Group  1830  CJHC  testing  -­‐  28/08/2015    Overview  

• The  purpose  of  this  testing  was  to  measure  excess  oxygen  (%),  CO  (ppm)  and  temperature  (°C)  at  the  central  jet  exit  plane  and  collect  visual  data  via  movies  and  OH*  chemiluminescence  photographs  at  a  series  of  coflow  conditions  and  central  jet  Reynolds  numbers.  

• Four  Reynolds  numbers  were  reviewed,  1k,  5k,  10k  and  15k.  For  each  Reynolds  number,  the  coflow  conditions  were  modified  by  changing  the  equivalence  ratio  (0.85,  0.78,  0.72,  0.65,  0.60,  0.53)  of  the  partially  premixed  auxiliary  burners,  and  adjusting  the  total  heat  input  of  the  system  (27kW,  23kW,  18kW).  

• The  equivalence  ratios  were  adjusted  at  each  heat  input  by  changing  the  compressed  air  flow  into  the  base  while  keeping  the  air  and  fuel  flow  rates  within  the  auxiliary  burners  constant.    

• The  heat  input  was  reduced  by  lowering  all  flow  rates  (base  and  aux  burner  air  flow,  and  fuel  flow),  initially  by  17%,  then  33%.    

• The  lower  boundary  of  equivalence  ratios  was  limited  by  a  maximum  flow  of  60%  into  the  base  of  the  combustor.    

• Previous  testing  showed  that  below  a  heat  input  of  18kW,  a  stable  flame  would  not  evolve.    

 Experimental  testing  apparatus    (CJHC  burner)    

   The   MILD   combustor   apparatus   can   be   broken   into   three   sections,   a   diffuser  cone   through   which   compressed   air   enters,   an   auxiliary   section   within   which  two   ring   burners   are   located,   and   a   primary   section  where   the   central   jet   exit  plane   is   located.   The   central   jet   (4.55mm   ID)   is   1450mm   long   and   is   height  adjustable  at  the  base.  The  jet  is  encased  by  two  concentric  tubes  that  allow  for  cooling  water   to  enter  and  exit  at   the  base  of   the  combustor   to  maintain  a   fuel  temperature  below  800K.  Both   the  auxiliary  (200mm  ID)  and  primary  sections  (200mm   ID)   are   insulated   with   a   Superwool   blanket   to   reduce   the   heat   loss  during  operation.  The  two  auxiliary  burners  have  been  manufactured  from  3/8th  

tubing   and   are   separated   by   a   140mm   distance.   The   lower   ring   burner   has   a  diameter   of   120mm  with   16   1mm   equispaced   holes.   The   upper   burner   has   a  diameter  of  150mm  with  16  1.59mm  holes.  The  ring  burners  were  designed  to  operate  in  partially  premixed  mode  and  create  hot,  dilute  exhaust  gases.  The  two  ring   burners   are   ignited   using   a   spark   plug,   located   above   the   lower   burner.  Downstream   is   the   primary   combustion   chamber   in   which   the   central   jet   is  located,   and   hot   diluted   exhaust   products   will   pass.   It   is   inside   this   primary  chamber   at   the   jet   exit   plane   that   data  was   collected.   To   enable   testing  within  this  plane,  an  extension  tube  (200mm  ID,  height  365mm)  was  manufactured  and  attached  to  the  lower  auxiliary  section  of  the  combustor.        Key  measurements  and  instrumentation    Key  measurement  =  Carbon  monoxide  and  %  excess  oxygen  Instrument  details=  Testo  350  XL  gas  analyser  (Serial  number:  01136751/510)    Key  measurement  =  Temperature  Instrument  details  =  Type  R  thermocouple  was  used,  with  readings  taken  from  a  thermocouple  reader  box  in  degrees  Celsius.      Key  measurement  =  Movie  photographs  (MP  files)  Instrument  =  Collected  using  a  Canon  60D  camera  via  remote  capture  software  with  15-­‐85mm  lens  set  to  85mm.  A  standard  UV  filter  was  used  in  front  of  the  lens.  Instrument  settings=       Exposure  time:       As  per  file  name     White  balance:       4000K     f-­‐number:       5.6     ISO:         6400      Key  measurement  =  OH*  chemiluminescence  Instrument  =  Collected  using  a  pco.PixelFly  CCD  mounted  to  a  Lambert  Instruments  image  intensifier  with  a  78mm  f/3.5  lens  (set  to  f/3.5)  and  through  an  Andover  310/10nm  bandpass  filter.  Timing  is  controlled  via  a  IDT  timing  hub.  Instrument  settings=       Exposure  time:       180ms     Intensifier  exposure  time:     As  per  file  name     Intensifier  gain:     maximum     Intensifier  delay:     20ms  relative  to  camera  trigger              CJHC  auxiliary  burner  configuration:  Bottom  burner:  120mm  diameter  ring  burner,  3/8th  pipe  diameter,  16  x  1.59mm  holes  

Top  burner:  150mm  diameter  ring  burner,  3/8th  pipe  diameter,  16  x  1mm  holes.    Note:  The  flow  is  split  evenly  between  the  top  and  bottom  ring  burners  via  installed  needle  valves  (Both  fully  open)      Plumbing:  Auxiliary  burners  fuel  (Natural  gas)  =  1/2  -­‐21-­‐GUSVT-­‐410  Auxiliary  burners  compressed  air  =  ½-­‐17-­‐GSVT-­‐44  Base  air  supply  =  ¾-­‐27-­‐GNSVGT-­‐54  (Separate  supply  to  auxiliary  burner)  Jet  fuel  supply  (Natural  gas)=  ½-­‐21-­‐GUSVT-­‐410  (Not  actually  1/2  –GUSVT-­‐410  float,  ran  out,  rather  a  ½-­‐B372-­‐V07,  but  does  not  exist  in  software  and  is  approximately  the  same  weight  as  the  GUSVT-­‐410  float)    Flowrates:  Air  (Base)=  %  Varied,  pressure  kept  constant  @500kPa(g)  Air  (Aux  burners)=  %  Varied,  kept  constant  @  120kPa(g)  Natural  Gas  (Aux  burners)=  %  Varied,  kept  constant  @100kPa(g)  Natural  Gas  (Central  jet)=  %  Varied,  kept  constant  @100kPa  (g)      ABB  FLOW  CHARTS    Base  Air    

   Aux  burner  air    

   Natural  gas    

       File  naming      OH*  chemiluminescence  files  and  flame  movies  were  saved  using  the  following  format:               MP_60_27_01k_030          First  part:  Either  OH  or  MP    (OH  =  OH*  chemiluminescence;  MP  =  movie  photograph)    Second  part:  Coflow  equivalence  ratio  (53  =  0.53  ER,    60  =  0.60  ER,  etc.)    

1st  Part   2nd  

Part  3rd  Part  

4th  Part  

5th  Part  

Third  part:  Coflow  heat  input  (18  =  18kW,  27  =  27kW)    [individual  files  saved  into  directories  based  on  first  three  parts]        Within  each  directory  the  files  are  each  saved  with  the  prefix  from  parts  1-­‐3,  followed  by:        Fourth  part:  Jet  Reynolds  number  (01k  =  1000,  15k  =  15,000)    Fifth  part:  Exposure  time  of  image  (for  OH*  value  in  millisecond,  e.g.  010  =  10ms,  150  =  150ms.  for  MP  value  in  inverse  seconds,  e.g.  030  =  1/30  sec,  125  =  1/125  sec).        

Appendix E Gaseq

121

122

123

Appendix F Flame Visual Analysis Results

Jet Reynolds number vs. excess oxygen (18kW)

φ = 0.53O2=9.3%T= 830◦C

φ = 0.60O2=7.8%T= 840◦C

φ = 0.65O2=6.7%T= 790◦C

φ = 0.72O2=5.3%T= 795◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

124

ofJet Reynolds number vs. Equivalence ratio (23kW)

φ = 0.60O2= 7.8%T= 850◦C

φ = 0.65O2= 6.7%T=870◦C

φ = 0.72O2= 5.3%T=870◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

125

ofJet Reynolds number vs. Equivalence ratio (27kW)

φ = 0.72O2=5.3%T= 940◦C

φ = 0.78O2=4.1%T= 950◦C

φ = 0.85O2=2.7%T= 970◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

ofJet Reynolds number vs. Equivalence ratio (18kW)

126

φ = 0.53O2=9.3%T= 830◦C

φ = 0.60O2=7.8%T= 840◦C

φ = 0.65O2=6.7%T= 790◦C

φ = 0.72O2=5.3%T= 795◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

127

ofJet Reynolds number vs. Equivalence ratio (23kW)

φ = 0.60O2= 7.8%T= 850◦C

φ = 0.65O2= 6.7%T=870◦C

φ = 0.72O2= 5.3%T=870◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

128

ofJet Reynolds number vs. Equivalence ratio (27kW)

φ = 0.72O2=5.3%T= 940◦C

φ = 0.78O2=4.1%T= 950◦C

φ = 0.85O2=2.7%T= 970◦C

Rejet=1,000

Rejet=5,000

Rejet=10,000

Rejet=15,000

129

Appendix G Pressure Calculations

130

Ap

pen

dix

HA

S1210

-P

T430

Ten

sile

Str

en

gth

133

134

Ap

pen

dix

IR

MS

S

135

Appendix J SOP for Start-up of Combustor

SAFE OPERATING PROCEDURE: MILD COMBUSTION TESTING (for project 1830)

Page 1 of 3 SOP No: Issue No:

LOCATION DETAILS School/Branch: Mechanical Engineering. Thebarton Research Laboratories TASK/ACTIVITY MILD COMBUSTION TESTING (for project 1830) Date: 29/04/15

PREPARED BY Name, Position and Signature (insert names of the supervisor, HSR, HSO and operator involved) Name

Fiona Lake Helen Hobbs Alexander Schumacher Dr Paul Medwell Richard Pateman Marc Simpson

Position Project Student Project Student Project Student Project Supervisor Workshop Manager Thebarton Laboratory Research Manager

Signature

HAZARD IDENTIFICATION: RMSS

RISK ASSESSMENT

MEDIUM

SAFE OPERATING PROCEDURE DETAILS

STOP DO NOT OPERATE PLANT IF YOU HAVE NOT COMPLETED (1) THE COMPULSORY UNIVERSITY OF ADELAIDE OCCUPATIONAL HEALTH AND SAFETY INDUCTION COURSE, AND; (2) DO NOT POSSESS THE REQUISITE QUALIFICATIONS OR TRAINING FOR THIS PIECE OF PLANT.

Preparation – work area check: ! Ready access to and egress from the machinery (min of 600mm clearance required) ! Area is free from grease, oil, debris and objects, which can be tripped over.

(Use diatomaceous earth (“kitty litter”) or absorption pillow to soak up grease, coolant, oil and other fluids) ! Area is clear of unauthorised people before commencing work. ! Ensure all operators/observers are aware of location of hot surfaces (by use of signage) ! Supervisor (or a suitable nominee) to be present at all times. ! Ensure all personnel are wearing appropriate clothing and closed-toe shoes. ! Verify location of fire extinguishers, and ensure test tags are current.

Personal Attire & Safety Equipment: ! Approved closed toe type shoes must be worn at all times. ! Approved safety spectacles/goggles must be worn at all times, where required. ! Clothing must be tight fitting. Protective overalls / attire with long sleeves / long pants to be worn (cotton materials). ! Long hair must be confined close to the head by an appropriate restraint. ! Finger rings and exposed loose jewellery (eg bracelets and necklaces) must not be worn. Medic Alert bracelet must be

taped if exposed. ! Leather gloves to be worn in immediate area around burner when hot.

152

SAFE OPERATING PROCEDURE: MILD COMBUSTION TESTING (for project 1830)

Page 2 of 3 SOP No: Issue No:

Safety Precautions that MUST be Observed: ! Visual inspection of burners, chamber, gas & air supply and flow distribution system (flow meters, valves, hoses, etc) to

verify it is in good operational order, ensuring no damage to any stationary or moving parts, electrical cords etc. Any unsafe equipment is to be reported to an authorised staff member and tagged out.

! Ensure all hoses connected correctly. ! Check natural gas system for leaks (by soap and water testing). ! Ensure lighting, water and power supplies are switched on at their respective main switches, where required. ! Be aware of other activities happening in the immediate area. ! Ensure that no slip and/or trip hazards are present. ! Ensure that lighting is adequate. ! Ensure burner location is directly below roof mounted exhaust extractor. ! Ensure all emergency exits are unlocked and free from obstruction. ! Ensure at least two people are present during testing. ! Ensure that the burner and equipment are securely mounted.

! Remove all flammable materials from the test area.

! Allow hot components to cool before manual handling and/or leaving test area.

! NEVER LEAVE COMBUSTOR RUNNING WHILST UNATTENDED.

Start-Up Operation: ! Check all valves fully shut.

! Check all pressure regulators fully closed.

! Check security of all components, fittings and hoses.

! Check extraction hood is positioned directly above the combustion chamber.

! Exhaust fan and air compressor switched on.

! Slowly open compressed air supply valve.

! Slightly increase air pressure in supply line to flow meter, air manifold and leak check and keep final needle valve closed.

! Slowly open natural gas supply valve.

! Slightly increase natural gas pressure in supply line to flow meter & gas manifold and leak check.

! Open air valve/s downstream of pressurised manifold (whichever valve/s are required for the test)

! Check air is now flowing into the base of the prelim burner section.

! Energise spark ignition system.

! Open natural gas manifold valve to preliminary burner, bottom burner only (not more than 30%).

! Safely check from a distance if the co-flow mixture has ignited, then de-energise spark ignition system.

! Adjust natural gas pressure and flow meter to required value.

! Adjust compressed air pressure and flow meter to required value.

! Slowly open air and natural gas manifold valves together (to preserve air/fuel ratio).

! Slowly open natural gas valve to uppermost prelim burner ring (if required).

! Check the stability of the flame, adjust air/fuel ratio if necessary to stabilise.

! Allow prelim burner to operate for no less than 2 minutes to warm up system.

SAFE OPERATING PROCEDURE: MILD COMBUSTION TESTING (for project 1830)

Page 3 of 3 SOP No: Issue No:

! Open natural gas valve to secondary combustion chamber to operation position.

! Look for signs of spontaneous auto-ignition in secondary combustion chamber.

! Monitor temperature (where applicable) and visually monitor apparatus for signs of excessive heat or failure.

! Adjust manifold air and natural gas valves as necessary to optimise performance.

! Record temperature readings once operating at steady state.

! Continue to operate system for as long as desired, looking for signs of failure/overheating.

! On completion of testing, follow shutdown procedure below:

Shut-Down Operation: ! Leave air and natural gas manifold valves in their last stable operating position. ! Close secondary combustion chamber manifold valve, wait 30 seconds for secondary combustion to extinguish. ! Close natural gas supply valve. ! Wait until the entire unit has been starved of fuel and all combustion has ceased. ! Close natural gas manifold valves once natural gas system has de-pressured. ! Leave air flowing through the system to slowly cool. ! Close compressed air source main valve and let air system de-pressure. ! Close air manifold valves. ! De-pressure any remaining lines and close secure regulators/ flow meters. ! Clean work area. ! Wait for unit to cool before handling.

General Safety ! Visual inspection of plant prior to use. Unsafe plant to be tagged out and reported to Workshop Manager. ! Keep all parts of your body and attire safely clear of the rotating and moving parts, at all times. ! Only authorised qualified staff to operate the burner. ! NEVER LEAVE BURNER RUNNING WHILST UNATTENDED. ! Closed Toe Type Shoes must be worn. ! Loose hair to be securely tied back, loose clothing to be rolled up and/or secured, loose jewellery to be removed. ! Hearing protection to be worn, where appropriate to the task being performed. ! Protective overall with long sleeves/ long pants to be worn (cotton materials). ! Leather Safety Gloves to be worn, where appropriate to the task being performed, and; ! Switch Off burner before leaving it unattended.

Note: This Safe Operating Procedure must be reviewed: a) after any accident, incident or near miss; b) when training new staff; c) if adopted by new work group; d) if equipment, substances or processes change; or e) within 1 year of date of issue.

Appendix K SOP for Installation and Removal of Insulation

SAFE OPERATING PROCEDURE: PRELIMINARY BURNER TESTING (for project 1830)

Page 1 of 3 SOP No: Issue No:

LOCATION DETAILS School/Branch: Mechanical Engineering. Thebarton Research Laboratories TASK/ACTIVITY Handling of Fibrous Ceramic Material (for project 1830) Date: 30/07/15

PREPARED BY Name, Position and Signature (insert names of the supervisor, HSR, HSO and operator involved) Name

Fiona Lake Helen Hobbs Alexander Schumacher Dr Paul Medwell Richard Pateman Marc Simpson

Position Project Student Project Student Project Student Project Supervisor Workshop Manager Thebarton Laboratory Research Manager

Signature

HAZARD IDENTIFICATION: RMSS 2488

RISK ASSESSMENT

MEDIUM

SAFE OPERATING PROCEDURE DETAILS

STOP DO NOT OPERATE PLANT IF YOU HAVE NOT COMPLETED (1) THE COMPULSORY UNIVERSITY OF ADELAIDE OCCUPATIONAL HEALTH AND SAFETY INDUCTION COURSE, AND; (2) DO NOT POSSESS THE REQUISITE QUALIFICATIONS OR TRAINING FOR THIS PIECE OF PLANT.

Preparation – work area check: ! Ready access to and egress from the machinery (min of 600mm clearance required) ! Area is free from grease, oil, debris and objects, which can be tripped over.

(Use diatomaceous earth (“kitty litter”) or absorption pillow to soak up grease, coolant, oil and other fluids) ! Area is clear of unauthorised people before commencing work. ! Prevent others from inadvertently entering the workspace ! Ensure a second operator is present and prepared to assist with the task ! Ensure all personnel are wearing appropriate clothing and closed-toe shoes. ! Ensure all equipment required for job completion is within reach ! DO NOT bring any food and/or drink into the workplace

Personal Attire & Safety Equipment: ! Approved closed toe type shoes must be worn at all times. ! Approved dust-proof goggles/safety spectacles with side shields must be worn at all times. ! Disposable coveralls or long-sleeve loose-fitting clothing must be worn at all times. ! Disposable footware for dust protection must be worn at all times. ! PVC or rubber gloves must be worn at all times. ! A Class P3 Respirator must be worn at all times and be well fitting.

155

SAFE OPERATING PROCEDURE: PRELIMINARY BURNER TESTING (for project 1830)

Page 2 of 3 SOP No: Issue No:

! Ensure exhaust extraction hood is positioned over work area and is functioning correctly

Operation of Emergency Equipment ! Check that the first aid kit has been properly maintained and is readily available and the operators are aware of its

contents and location ! HEPA filter vacuum must be checked, powered and emptied before use.

Machine Pre-operational Safety Checks – Safety Precautions that MUST be Observed: ! Ensure lighting and power are switched on their respective main switches, where required.

! Be aware of other activities happening in the immediate area

! Ensure that no slip and/or trip hazards are present

! Ensure that machine lighting is adequate

! Ensure that the work area is sectioned off using barriers

! Ensure both operators visually identify the location of ALL emergency equipment (i.e vacuum, first aid kit)

! Check all personnel involved are wearing appropriate PPE for task being performed (i.e safety goggles, respirators, clothing)

Cutting and Application of Ceramic Fibre Insulation: ! Use extraction and ventilation systems with filtration to prevent dust and fibre dispersion. ! Carefully remove ceramic fibre material from packaging ONLY when needed. ! Prevent further dust dispersion by damping the materials with clean water mist. ! ONLY use hand tools to cut materials in size to minimise dust creation ! Use a sharp steel blade to cut material ! Install the materials to surface with gloves on ! Apply foil layer and secure materials with tie wire

Removal of Ceramic Fibre Insulation: ! Use extraction and ventilation systems with filtration to prevent dust and fibre dispersion. ! Carefully remove wire holding foil layer in place ! Carefully remove the foil layer ! Prevent further dust dispersion by damping the materials with clean water mist. ! Remove insulation from the combustor ! Place the used insulation in a synthetic mineral fibre disposal bag (this will be disposed in a hazardous material waste

bin)

Post Cutting and/or Application and/or Removal Procedure: ! Repacking and safely storing unused materials in original packaging and re-seal the container. ! Use HEPA filter vacuum to remove debris, dust and excess materials from the work area. ! DO NOT use compressed air, high pressure water spray and dry brushing for cleaning. ! DO NOT flush spillage to drain and prevent from entering natural watercourses. ! Clean by wet sweeping or wiping ! Check the final application to ensure all insulation is properly secured and protected by the outer foil layer. ! Remove protective clothing and dispose of in a sturdy plastic bag and laundered separately from other clothing. ! P3 respiratory protection to be removed after disposable coveralls. Wipe with a wet cloth before removal. ! Wash hand thoroughly after handling

SAFE OPERATING PROCEDURE: PRELIMINARY BURNER TESTING (for project 1830)

Page 3 of 3 SOP No: Issue No:

! Take particular care to ensure dust and fibre are not released when emptying waste bins.

General Safety ! Visual inspection of plant prior to use. Unsafe plant to be tagged out and reported to LAB manager ! Safety glasses must be worn at all times during the operation ! Respirators must be worn at all times during operation ! Closed toe type shoes must be worn during operation ! PVC or rubber gloves must be worn when handling the materials

Note: This Safe Operating Procedure must be reviewed: a) after any accident, incident or near miss; b) when training new staff; c) if adopted by new work group; d) if equipment, substances or processes change; or e) within 1 year of date of issue.