Study of Hybrid Combustion using Paraffin Wax Fuel and N2O/N2O4 as

Oxidizer

BY

Sandeep PatnalaME/SER/1022/09

UNDER THE GUIDANCE OFDr. P.C. JOSHI

DEPARTMENT OF SPACE ENGINEERING AND ROCKETRYBIRLA INSTITUTE OF TECHNOLOGY, MESRA

INTRODUCTION

In Hybrid Propulsion Systems one component of the propellant is stored in liquid/gaseous phase while the other is stored in solid phase

Depending on the physical states of fuel and oxidizer the hybrid system is divided in to Direct and Reverse hybrid propulsion system.

The specific impulse for hybrid rockets can range from 275 - 350 sec.

Direct Hybrid Reverse Hybrid

Oxidizer : Liquid Oxidizer : Solid

Fuel : Solid Fuel : Liquid

Hybrid Rocket Configuration

Advantages of Hybrids

Compared to SOLIDS LIQUIDS

Simplicity -Chemically Simpler -Mechanically Simpler

Safety -Reduced Chemical Explosion Hazards-Thrust Termination and abort possibility

-Reduced fire hazards

Performance Related -Better Isp performance-Throttling/Restart Capability

-Higher Fuel Density-Easy inclusion of solid performance additives

Other -Reduced environmental impact

-Reduced mass of the liquid

Cost -Reduced development costs are expected

Hybrid rockets also exhibit some disadvantages when compared to Liquid and Solid Rockets

Oxidizer-to-Fuel ratio shift. Low regression rate. Uneven regression rate along the length of the grain.

The primary hazards associated with hybrids are: Blow back. Hard starts.

Disadvantages of Hybrid Rockets:-

Objective

To study the following combustion characteristics of paraffin wax and nitrous oxide/nitrogen tetroxide hybrid system

1. Regression rate at different injection pressures2. Mass consumption rate at different injection pressures3. Pressure-Time history of hybrid rocket motor4. Thrust and Specific impulse of above hybrid system

Methodology

Literature review Design and fabrication of the rocket motor, mould with

mandrel and nozzle Theoretical Analysis Preparation of N2O4

Experimental work Results

Literature Review

M.A.Karabeyoglu, D.Altman ---> Ref (1)i)For several classes of liquefying fuels, the layer is hydro dynamically

unstable leading to substantial droplet entrainment from the melt layer into the gas stream.

ii) The susceptibility of a given fuel to this shear driven instability increases with decreasing viscosity and surface tension of the melt layer.

iii)For practical oxidizer flux levels encountered in hybrid rocket applications, droplet entrainment can dominate direct gasification.

iv)Several methods for increasing regression rates in hybrids were tested.

Liquid Layer Combustion TheoryA) Liquid Layer Thickness Estimation :

The thickness of the energy liquid layer can be determined by the energy transfer relations in the solid and liquid phases.

To estimate the liquid layer thickness following assumptions are made 1) Steady state regression rate of the slab2) Physical properties of the material in both liquid and

solid phase are uniform.3) The effect of convection in the liquid layer is ignored.

The possibility of the penetration of the thermal radiation into the fuel slab is analyzed and several assumptions are made in the radiation treatment, which are

1) Radiative flux is one dimensional.2) Since the temperature levels in the slab are small, the

contribution of radiation emitted by internal material to the radiative intensity is negligable.

3) The absorption coefficient of both liquid and solid material behaves like a gray body.

Under these simplifying assumptions, the thermal analysis yields the melt layer thickness as

-----> (1)The thickness parameter ψ mainly depends on : thermo

physical properties and radiative characteristics of the fuel.

The characteristic thermal thickness in the liquid phase is defined as -----> (2)

Ψ can be found as a solution of the following nonlinear equation -----> (3)

Here the following definitions of the effective heating parameters are introduced for convenience.

----> (3a,3b,3c)

Ta, Tm, Tv =Initial, Melting and Vaporization temperatures of the fuel, respectively.

Qr and Qw =Radiative and Total heat fluxes to the fuel surface.

Cl and Cs =Average specific heats of the liquid and solid.

Lm and Lv =latent heats for melting and vaporization.

r and rv = Total and vaporization components of the regression rate

Another parameter that appears in the thickness expression is the non-dimensional radiation parameter, Rl, which is defined as the ratio of the thermal thickness to the radiative thickness in the liquid phase.

------> (4)where, ‘a’ is the average gray body absorption coefficient in the liquid phase.

An explicit solution for the algebric nonlinear equation, eqn(3), for the general case could not be obtained.

The two limiting cases are :1) Rl >>1, the absorption of the radiation in the liquid layer is very large. The

thickness can be solved explicitly as

----> (5)

All the thermo physical properties of the fuel material are lumped in the logarithmic term and the Qr/Qc ratio does not affect the thickness. This case is important for propellants that are loaded with strongly absorbing material such as carbon black.

2) Rl <<1, the absorption of the radiation in the liquid phase is small. The thickness of the thermal layer in the liquid is much smaller than the radiative thickness in the liquid and as a consequence all the radiative flux is absorbed in the solid. Unlike the other extreme, in this case the film thickness depends on the ratio of radiative heat flux to the convective heat flux and it can be expressed as

• ----> (6)

B) Liquid Entrainment Relationships:The entrainment component of the regression rate depends on the parameters expressed belowAccording to Gater and L’Ecuyer entrainment mass transfer rate,

-------> (7)Where rent – entrainment portion of the regression rate Xe -- entrainment parameter

mL -- liquid flow rate per unit area with in the melt layerIn the light of the experimental findings and the results of the linear theory, a general empirical expression for the entrainment rate of liquid droplets in terms of the relevant properties of the hybrid motor is,

Mass Transfer Mechanism

L.M.C.Santos , L.A.R.Almeida ---> ref (2)

I. This paper deals with the combustion of ultra-high molecular weight polyethylene, and paraffin as the solid fuels burning with gaseous oxygen as well as N2O as the oxidizers.

II. HTPB has been the preferred solid fuel for hybrid propulsion as the majority of experimental work shows.

III. High density polyethylene in the pressure range of 20-40 bar resulted in regression rates no higher than 0.3mm/sec, while paraffin and oxygen with oxidizer mass flux ranging from 2 to 10g/cm2 s resulted in 1.0 mm/sec.

Tsong-Sheng Lee and Hsin-Luen Tsai ----> ref(3)

I. A series of Paraffin-HTPB based nitrous oxide hybrid rocket fuels have been studies experimentally in a laboratory scale motor.

II. About 3 to 4 times the regression rate is increased by burning paraffin wax as compared to regression rates of HTPB swirling O2 hybrid system as oxidizer mass flux at 90kg/ m2 sec.

III. Isp of 50p fuel can reach up to 220sec wit oxidizer mass flux of 110kg/ m2 sec. Lower regression rate of HTPB fuel resulted in a lower Isp value and presenting fuel-lean combustion as oxidizer mass flux went beyond 80kg/ m2 sec due to part of the oxygen ejecting through nozzle directly without reacting with fuel vapors.

Alexandra Lazarav, Alon Gray ----> ref (4)

I. The paper presents an experimental investigation of a laboratory hybrid motor employing paraffin fuel and gaseous oxidizer.

II. Several types of paraffin has been tested and it is said that paraffin fuels have poor mechanical characteristics. This was over come by adding polymer to paraffin .

III. Plain Paraffin :-Some fuel was blown through the nozzle, unburned, thus reducing the performance, while some fuel was accumulated in the motor.

Results of Static firing experiments with plain paraffin as fuel

Paraffin and Polymer mixture fuel :Several ideas were proposed to improve paraffin based fuel characteristics,

performance and regression rate. Among those ideas adding nano sized aluminum particles and carbon black to the plain paraffin improved mechanical properties. Thus improved density specific impulse and enhanced linear regression rate.

Results of static firing experiments with paraffin wax and polymer mixture as fuel

Work Done

Literature survey

Design and modification of Combustion Chamber

Design and fabrication of Mandrel, Case, Cover, Base Plate

Design of Nozzle

Evaluation of the performance parameters

A small quantity of N2O4 has been Prepared

Work to be done

Preparation of N2O4

Preparation of fuel Grain

Experimental work

Results and discussion

Procedure for the preparation of N2O4

Step 1 :-NaNO3

1. NaNO3 is placed in an open pan in an oven at approx 315°C for 20minutes or at a lesser temperature for a longer period.

2. Care has to be taken to ensure that the temp remains below the decomposition temperature of NaNO3 ( 380°C).

MnSO4

3. MnSO4 is roasted in an open pan in an oven for an hour at 315°C. Step 2 :- 1. The powders are placed in a separate bag and are pound into

pieces.2. 155gm of MnSO4 and 170gm of NaNO3 are mixed thoroughly and

they are rolled to ensure proper mixing.

Step 3 :-1. The ingredients( reactants) are pound in a high temperature

resistant vessel.2. The vessel is heated to produce vapors which are cooled using a

condenser and an ice bath to get liquid N2O4.

Dinitrogen Tetroxide Preparation Apparatus

Test Rocket Motor

Base Plate

Mandrel

Case

Cover

Convergent –Divergent Nozzle

References

Karabeyogul, M.A., Cantwell, B.J., and Altman,D., “ Development and Testing of Paraffin-Based Hybrid Rocket Fuels”, AIAA/SAE/ASME/ASEE, 37th Joint Propulsion Conference and Exhibit, July 8-11, 2001, Salt Lake City, Utah, AIAA-2001-4503.

Alexandra, L., Alon Gany “Experimental Investigation of Paraffin-Fueled Hybrid Combustion”, Third European Combustion Meeting 2007.

L.M.C.Santos., L.A.R.Almeida, A.M.Fraga and C.A.G.Veras “Experimental Investigation of a Paraffin based Hybrid Rocket” .

Karabeyoglu, M.A., Altman, D., Cantwell, B.J., Patent Pending, “High Regression Rate Hybrid Rocket Fuels”, US Patent,1999.

McCormick, Anthony et al.,“Design, Optimization, and Launch of a 3” Diameter N2O/ Aluminized Paraffin Rocket”, 41st AIAA/ ASME/ SAE/ ASEE Joint Propulsion Conference & Exhibit; Tucson, AZ; USA; 10-13 July 2005. pp. 1-14-2005.

Tsong-Sheng Lee., Hsin-Luen Tsai.,”Fuel Regression Rate in a Paraffin-HTPB Nitrous Oxide Hybrid Rocket”, 7th Asian-Pasific Conference on Combustion; Nation Taiwan University, Taipei, Taiwan;24-27 May2009.

Martin J. Chiaverini; George C. Harting; Yen-Cherng Lu; Kenneth K. Kuo.,” Combustion of Solid Fuel Slabs with Gaseous Oxygen in a Hybrid Motor Analog” NASA-CR-201116.

Chatterjee,A.k., and Joshi,P.C., “Length and Port Size Effect on Combustion of PVC Plastisol Hybrid Fuel,” Propellant and Explosive Journal, Vol.15, 1980, pp.163-167.

Chatterjee,A.K., “Some Combustion Studies of PVC-O2 Hybrid Systems”, Thesis of Masters of Science in Space Engineering and Rocketry, Birla Institute of Technology, Mesra, Ranchi, India,1972.

Matthas Grosse., Bad Reichenhall., “ HERA experimental rocket project”.

Marxman,G.A., Wooldrige,C.E., and Muzzy,R.J., “Fundamentals of Hybrid Boundary Layer Combustion”, Progress in Aeronautics and Astronautics, Vol.15,AIAA,New York., 1966,pp.269-289.

Martin J.Chiaverini., Kenneth K.Kuo., Aeretz., and George C.Harting., “ Regression-Rate and Heat-Transfer Corellations for Hybrid Rocket Combustion”, Journal Of Propulsion And Power, Vol.17.No1, January-February2001.

Phimon George., Krishnan.S., Varkey.P.M., Ravindran.M., and Lalitha Ramachandran., “ Fuel Regression Rate in Hydroxyl-Terminated-Polybutadiene/Gaseous-Oygen Hybrid Rocket Motors”, Journal Of Propulsion And Power, Vol.17.No.1, January-February2001.

Rajeshwar Dayal Swami., Alon Gany., “ Analysis and Testing of Similarity and Scale Effects in Hybrid Rocket Motor”, Science Direct, Acta Astronautics 52(2003),pp.619-628.

Potapkin.A.V., and Lee.T.S., “ Experimental Study of Thrust Performance of a Hybrid Rocket Motor with Various Methods of Oxidizer Injection”, Combustion, Explosion, and Shock Wave. Vol.40, No.4,pp.386-392,2004.

Michael Harris., Bruce Helming., Jacob Teufert “PANTHR Paraffin and Nitrous-Oxide test Hybrid Rocket”,MAE 4291,2006.

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