National Conference in Mechanical Engineering Research and Postgraduate Studies (2nd NCMER 2010)3-4 December 2010, Faculty of Mechanical Engineering, UMP Pekan, Kuantan, Pahang, Malaysia; pp. 580-596ISBN: 978-967-0120-04-1; Editors: M.M. Rahman, M.Y. Taib, A.R. Ismail, A.R. Yusoff, and M.A.M. Romlay©Universiti Malaysia Pahang

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EXPERIMENTAL AND MODELINGINVESTIGATION OF THEPERFORMANCE CHARACTERISTICS ON DIESEL HCCI WITH

HYDROGEN ADDITIVE- A REVIEW

E.E. Supeni1, T.F. Yusaf2 , A.P. Wandel2 , D.R. Buttsworth2 and M.M. Noor3

1Department of Mechanical & Manufacturing Engineering,Faculty of EngineeringUniversiti Putra Malaysia,43400 UPM, Serdang, Selangor, Malaysia

Email: eris@eng.upm.edu.my2Faculty of Engineering and Surveying,University of Southern Queensland

Toowoomba, QLD 4350, Australia3Automotive Engineering Center, Faculty of Mechanical Engineering, Universiti

Malaysia Pahang,26600 UMP, Pekan, Pahang, MalaysiaEmail: muhamad@ump.edu.my

ABSTRACT

Homogeneous charge compression ignition (HCCI) combustion has been attractingconsiderable attention due to higher efficiency with lower nitrogen oxide (NOx) andparticulate matter (PM) emissions. The combustion process in dual fuel systems inHCCI engines is very complex due to the interactions of mixing and chemistry insidethe combustion chamber during the late stages of the compression stroke and theignition process. The ignition process is very critical with significant heat release fromchemical reactions occurs and the timing is difficult to predict. Controlling auto ignitionwas considered as the significant problem to HCCI especially in tackling the suddenpressure rise in-cylinder. Thus, it will affect the performance and emission that varieswith the operating engine condition and fuel properties. The sudden pressure is due toheterogeneous which result in flame propagation.This paper mainly reviewson dualfuels in internal combustion engine, with a particular focus on using hydrogen as a fueladditive.

Keywords: HCCI, combustion, nitrogen oxides, particulate matter.

INTRODUCTION

The continuous engine and fuelresearch to ensure more efficient combustionand lessemission emitted are always the priority. HCCI potentially carryout ultra-lean burningunder higher compression compare to conventional spark ignition and elimination ofNOx and particulate matter (PM) much better than diesel engines. (Najt and Foster,1983;Thring, 1989; Christensen, et al. 1997; Takeda and Niimura, 1996; Ogawa, 1998;Yamasaki and Iida, 2002; Harada et al., 1998; Chen, 2000; Christensen and Johansson,1999; Kaneko et al., 2002; Ogawa et al., 2003a, Ogawa et al. 2003b) The HCCI idea hasreceived a great attention recently due to its thermal efficiency and potential for lowemissions of particulate matter (PM), less brake specific fuel consumption (BSFC) andnitrogen oxide (NOx) (Stanglmaierand Robert, 1999).However, it still producesunburnthydrocarbon (UHC) and carbon monoxide (CO) due to low temperature and knockswhich depend on the operating condition.

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For several decades, a considerable amount of research effort has gone into theinvestigation of HCCI combustion, especially with diesel fuel, where the difficulty toachieve diesel HCCI combustion without accessory methods stands out. Severalpotential control systems have been proposed to control the HCCI combustion modewithout changing the cetane number of diesel fuel (Nebjosaand Rui, 2001). Nowadays,using hydrogen as an additive has also been popular in market since the hydrogeneconomy has been introduced. But, there have been several arguments on efficiency andpractical used. Recent claims of engine efficiency improvement via hydrogen on boardgenerated by small electrolysers have been made by numerous businesses selling thesedevices (Bari and Mohammad, 2010).The technical literature indicates that usinghydrogen in spark ignition and compression ignition results in some improvement inengine emissions. But the literature with detailed experimental results with hydrogensupplementation in a stationary HCCI diesel engine generator set was not found(Vamshi et.al, 2009). The experimental investigation will be carried out in order by theauthor to investigate the performance characteristics of the HCCI diesel engine withhydrogen additive. The USQ hydrogen generator will be used to supply hydrogen intointake port manifold in a single diesel engine is modified to run on HCCI mode.

Early direct injection HCCI requires carefully designed fuel injector to minimizethe fuel wall-wetting that can cause combustion inefficiency and oil dilution. Late directinjection HCCI requires a long ignition delay and rapid mixing rate to achieve thehomogeneous mixture (Ganesh and Nagarajan, 2010). This is of course will result inmajor modification on spray angle and penetration. In presence of hydrogen, it willenhance the complete combustion take place. Mixing hydrogen with hydrocarbon fuelsprovides combustion acceleration by increasing the rate of molecular-crackingprocesses in which large hydrocarbons are broken into smaller fragments (Roy, 1998).Expediting production of smaller molecular fragments is beneficial in increasing thesurface-to-volume ratio and consequent exposure to oxygen for completion of thecombustion process. Relatively small amount of hydrogen can dramatically increasehorsepower and reduce emissions of atmospheric pollutants.

HCCI has been studied due to its low-temperature combustion technology.HCCI involves the auto-ignition of a homogeneous mixture of fuel and premixed atlow-to-moderate temperatures and high pressure (Zhao, 2007). This approach enablesthe engine to have a high compression ratio (CR), minimize air throttling losses, andrapidly burn the fuel-air mixture near top dead center (TDC), which results in a highthermal efficiency. Meanwhile, the burning of a homogeneous fuel-lean mixture atrelatively low-temperature reduce the formation of PM and NOx, the two problematicemissions from conventional diesel engines. These remarkable combustioncharacteristics make HCCI a promising combustion candidate for internal combustion(Stanglmaierand Roberts, 1999; Lu and Huang, 2005; Onishiet al., 1979). It was firstdiscovered in 1979 by Onishi et al. (1979) as a method of reducing emissions and fuelconsumption of two-stroke engines at part-load conditions as applied in the ActiveThermo Atmosphere Combustion engine (ATAC). In 1983, Najtet al. performed HCCIexperiment with a four-stroke engine: the first to apply the HCCI combustion concept ina four-stroke gasoline engine with the exhaust gas recirculation (EGR) concept. Theydiscovered that this reduced NOxand improved the efficiency (Najtet al., 1983).

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HCCI PRINCIPLES

HCCI is classified as an engine where the fuel and air are mixed homogenously andcharged before combustion starts and the mixture spontaneously auto-ignites as a resultof the temperature increase in the compression stroke (Fig. 1). Thus HCCI is similar toSI in terms of both engines using a premixed charge yet similar to CI as both rely onauto-ignition to initiate combustion (Fig.2). The ideal HCCI combustion is characterizedby low-temperature, lean combustion which is generated at various points throughoutthe cylinder due to the lean nature of the combustion, and the lack of flame propagation.(Ghazikhaniet al., 2009).HCCI combustion has the potential to simultaneously reduceNOx emissions and also reduce PM, which are customarily problems in compressionignition engines (Zhao, 2007). However, the unburnt hydrocarbon (UHC) and carbonmonoxide (CO) emissions are still high which is due to lower peak temperatures, as inSI.This are caused by incomplete oxidation due to the rapid combustion events, low in-cylinder temperatures and trapped crevice gases (Aceves et. al., 2004).

Figure 1: Start of combustion of three types of engines (Aceveset al., 2004).

Figure 2: Original HCCI concept(United State Department of Energy, 2001).

High PressureFuel Injection

Spark Ignition withModerate Pressure FuelInjection

injector

Low PressureFuel InjectionNo Ignition System

injectorSpark plug

DiffusiveFlame

PremixedHomogeneous

PremixedFlame

injector

1) Intake of a premixed charge 2) The charge is compressed

4) Spontaneous auto-ignition 3) The charge is compressed further

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PROBLEM ENCOUNTERED

In conventional diesel engine, the speed of the chemical reaction is incomparably fasterthan the speed of the mixing of the fuel and air. NOxand PM are accordingly generateddue to incomplete the mixing process before combustion begins.To overcome thisobstacle, it is desirable to enhance the mixing process before combustion begins, and toburn the fuel in a lean homogeneous state. Due to extremely lean nature of thecombustion, and the lack of flame propagation, HCCI combustion has the potential tosimultaneously not only reduce nitrogen oxide emissions but also reduce total unburnthydrocarbons, which is traditionally a problem in compression ignition engines.Therefore, HCCI combustion is more efficient than traditional compression ignitioncombustion. However, an ongoing developmental problem with HCCI engines iscontrolling the combustion process such auto-ignition (Nakagomeet al., 1998;Yanagiharaand Mizuta, 1996; Akagawaet al., 1999; Nishijimaet al., 2001; Kimura et al.,1999).

In this regard, ongoing research has been undertaken in order to tackle theproblem, particularly in controlling the combustion process such as auto-ignition.Traditional petrol engines use a spark to ignite the mixture and diesel engines use theinjection of the fuel at high compression to achieve this. With HCCI combustion asshown in Fig. 1, this auto-ignition point must be controlled without either a spark or latefuel injection but using only the charge mixture composition and the temperature history(U.S DOE,2001). This has led to the development of various techniques including theuse of high levels of exhaust gas circulation (EGR), variable valve actuation (VVA),variable induction temperature (VIT) and variable compression ratio (VCR).Theproblem is that none of these methods allow for HCCI combustion to operate over asufficient range of loads and speeds. The concept of HCCI is further explained in Fig. 2.Research conducted with the use of optical diagnostics has shown that HCCIcombustion initiates simultaneously at multiple spots within the combustion chamberand that there is no distinguishable flame propagation (Warnatzet al., 2006).

HYDROGEN AS COMBUSTION ADDITIVE

Hydrogen ignites more rapidly than hydrocarbon fuels because it is the lightest atomthat incorporates combustion reactions at higher flame speed, has lower activationenergy, and incurs more molecular collisions than heavier molecules. This uniquenessmakes it possible to use mixtures of hydrogen with conventional HC fuels such asgasoline, diesel and natural gas to reduce emissions of UHC. A small amount ofhydrogen addition produces a combustible mixture which can be burned at anequivalence ratio below the lean flammability limit of fuel/air mixture. Therefore, lowertemperatures prevail which means lower NO. Emission and lower heat transfer to thewalls. Also, at partial loads, lower throttling is needed and pumping work islowered.The high molecular diffusivity of the hydrogen into the air improves themixture uniformity and, hence, the combustion efficiency, and the cycle to cyclevariation as shown in Table 1. Some researchers investigated diesel engines, usinghydrogen as a sole fuel. However; it was very difficult to run a diesel engine withhydrogen just by increasing the compression ratio, due to its high self-ignitiontemperature. Glow plug or spark plug is regularly used (Wong, 1990). Ikegami et al.(1982) investigated the hydrogen combustion with a special injector that was equippedwith a glow plug and obtained moderate engine performance. Therefore, hydrogen is

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used as a sole fuel in spark ignition engines. Hydrogen powered S.I. engine has acomparable power output with gasoline, with higher efficiency (Naberet al., 1998). Theconcept of using hydrogen as an alternative to diesel fuel in C.I. engines is a recentdevelopment. As the self-ignition temperature of hydrogen (858 K) is higher than diesel(453 K), hydrogen cannot be ignited by compression. Hence it requires the use ofexternal heat source like spark plug or a glow plug.

Table 1: Properties of hydrogen and diesel (Saravanan and Nagarajan, 2007).

RECENT EXPERIMENTAL STUDIES

There has been a lot of research on dual-fuel hydrogen diesel but most of them it on DIgasoline and DI diesel rather than HCCI. Although the principles of neither combustionnor the engine specification are the same, useful lessons may be learned. Karimetal.(1996) carried out study on the effect of addition of some hydrogen to the methane,speeds up the rates of initiation and subsequent propagation of flames over the wholecombustible mixture range, including for very fast flowing mixtures. This enhancementof flame initiation and subsequent flame propagation reduces the ignition delay andcombustion period in both spark ignition and compression ignition engines whichshould lead to noticeable improvements in the combustion process and performance.

A significant performance and emission has been discovered by Antuneset al.(2009) when injecting hydrogen to diesel fuel at ratio of 20 % diesel fuel and 80 %hydrogen (on an energy basis).It has been found that with the hydrogen-fueled engineobtaining a fuel efficiency of approximately 43 % compared to 28 % in theconventional, diesel-fueled mode. A reduction in nitrogen oxides emission formation ofapproximately 20 % has also been observed. Those figures indicate the combustion ofhydrogen with diesel is better than conventional fuel in term of performance and

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emission.Masood and Ishrat (2007)had carried out a comparative study to analyze theeffect of direct injection and port injection of hydrogen into the combustion chamber.Based on the study, it was found that there was significant improvement in term ofcombustion efficiency, reduce misfire, reduce emission as well as reduce fuelconsumption particularly in the injection port rather in direct injection. This has beenalso accomplished by both works have shown a good agreement as simulatedtheoretically and experimentally.

Saravanan and Nagarajan(2010) investigated hydrogen–diesel dual fuel in adiesel engine.. Hydrogen was injected in the range from 10 % to 90 % by volume.Throughout the research, knock can occur if only the hydrogen enrichment equals 50 %or more at full load of the engine. Furthermore, it was also found that lowerhydrocarbons (HC), NOx emission as far as exhaust emission was concerned. It can betemperature dependence of the auto-ignition delay is weak, and the auto-ignition delayreaches a limited value. Welch (1990)conducted investigations on hydrogen combustionby its auto-ignition with glow plug assist in a reciprocating engine at a compressionratio of 17. Results indicate that the hydrogen fueled diesel engine can generate higherpower than an ordinary diesel engine due to the absence of smoke emissions. Anotherpositive aspect is reduced NOxemissions compared to the ordinary diesel engine.Saravanan and Nagarajan in other work, tested onsingle cylinder water cooled DI dieselengine having a rated speed of 1500 rpm developing 3.7 kW was converted to operateon dual fuel mode with hydrogen running on timed manifold injection and timed portinjection technique.

The optimized data for port and manifold has been found injection at 5º beforeTDC with injection duration of 30º CA with hydrogen flow rate of 7.5 liters/min andinjection at gas TDC)with injection duration of 30º crank angle (CA) with hydrogenflow rate of 7.5 litres/min respectively.Masood and Ishrat studied the effect of dual fuelhydrogen diesel DI. Fig. 3 shows the brake thermal efficiency for the induction throughinlet manifold increased the percentage substitution of hydrogen both methods;however, the efficiency was higher by around 5% in induction through inlet manifoldwhen compared to that of direct injection method. This is mainly due tocompletely uniform mixing by the induction method, which formed a homogeneousmixture that was burnt completely by the flame initiated by the diesel injection andtherefore resulted in complete heat release. The peak heat release by using the inductionmanifold was also higher than for the injection manifold as depicted in Fig. 4. This isdue to the rapid and instantaneous combustion that took place at high hydrogen additionin the induction manifold whereby homogenous combustion occurred.

The use of premixed hydrogen in the intake air in DI resolves this difficulty ofpoor ignition delay, since the DI studied by Saravanan and Nagarajan wherebyhydrogen may enhance the combustion of the fuel. Fig. 5 illustrates the pressure crankangle diagram at full load for a hydrogen dual-fuel engine using port injection andmanifold injection. The peak pressure obtained for hydrogen operation at full load was83.4 bar in port injection and 81.8 bar in manifold injection, whereas in the case ofdiesel it was 82.2 bar. The peak pressure in manifold injection was reduced by 2%compared to port injection which is due to the better mixing of air and fuel in manifoldinjection. The peak pressure in hydrogen port injection and manifold injection wasadvanced by 5° and 4° CA respectively compared to diesel peak pressure. The advancein peak pressure in a hydrogen-operated engine is due to faster combustion sincehydrogen has a high flame speed.

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Meanwhile, Szwaja and Rogalinski studied hydrogen enrichment up to 25%addition. In Fig. 6, diesel fuel is the reference curve for hydrogen addition. The peakpressure increases with hydrogen doses of 5%, 15% and 25% respectively at constantdiesel dose, as a result of the extra energy delivered to the combustion chamber.Furthermore, it increases the rate of in-cylinder pressure rise lower during combustion.The value of the peak pressure increased with the increasing hydrogen and was reachedsooner, indicating more rapid combustion. It was found that the knock phenomenon isshown in Fig. 7. It had been observed that there wasunburnt gas ahead of the flame thatcompressed as the flame propagated and the pressure in the combustion chamber rose.The high pressure and corresponding high temperature of unburnt reactants can causepinging and knocking to spontaneously happen. It can be summarized all the previousexperimental carried out study the effect on the dual fuel of hydrogen-diesel usingconventional diesel engine particularly in performance and emission. The thermalefficiency consistently increased. But, some of them argued with the findingsparticularly in emissions. These differences obtained might due to uncontrolledparameters for example geometric configuration, assumed fuel-injector characteristics,and simplified chemical kinetics and other physical models.

Figure 3: Brake thermal efficiencyversus % H2 (Masood and Ishrat, 2007)

Figure 4: Heat release rate versus CrankAngle (Masoodand Ishrat, 2007)

Figure 5: Pressure crank-angle diagram atfull load (Szwaja and Rogalinski, 2009)

Figure 6: In-cylinder pressure traces forVarious hydrogen energy fractions

HCCI (Szwaja and Rogalinski, 2009)

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Figure 7: In-cylinder pressure versus crank angle for hydrogen combustion undertheHCCI (Szwaja and Rogalinski, 2009)

RECENTMODELING STUDIES

There have been several studies regarding HCCI modeling particularly in single fueldiesel but not so many for dual fuel hydrogen-diesel. Most of the studies discussed onthe fundamental theory of modeling before it was tested. Strategies, research anddevelopment on HCCI was deliberately discussed by Mingfaet al. (2009) Five types ofmodels to HCCI engine modeling has been described in this paper. The models are asfollows :-zero-dimensional single-zone models with detailed chemistry, quasi-dimensional multi-zone with detailed chemistry, one-dimensional engine cycle withdetailed chemistry ,multi-dimensional CFD with multi-zone detailed chemistry andmulti-dimensional CFD with detailed chemistry.

Soyluand Gerpen (2003) has developed a zero dimensional thermodynamicmodel that contains a simple heat release sub-model and an auto ignition model wasused in a predictive fashion to better understand the in-cylinder processes and theefficiency potential of a natural gas engine in the HCCI mode. The model has been usedfor parametric studies to evaluate HCCI control strategies that can be tested on theresearch engine. The results indicated that if the initial conditions of the mixture areknown precisely at intake valve closing, the auto ignition timing is controllable.Ogawaet al. (2005) conclude on their studies that the control of ignition timing, suppression ofexcessively rapid combustion, and expansion of the operating load ranges to a levelcomparable to ordinary naturally aspirated diesel operation is achieved with directinjection of ignition inhibitors in an HCCI engine. Salvador et al. (2001)developed twopowerful tools: a single zone model and a multi-zone model. The single zone model hasproven very successful in predicting start of combustion and providing reasonableestimates for peak cylinder pressure, indicated efficiency and NOx emissions. Thismodel is being utilized to develop detailed engine performance maps and controlstrategies, and to analyze the problem of engine stability. The multi-zone model iscapable of very accurate predictions of the combustion process, including HC and COemissions.

Kong has investigated the HCCI engine combustion with consideration ofturbulent mixing effects. Throughout his study, detailed chemical kinetics was used inan engine CFD code to study the combustionprocess in HCCI engines. The CHEMKIN

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code was implemented in KIVA such that thechemistry and flow solutions werecoupled. The reaction mechanism consists of hundredsof reactions and species and isderived from fundamental flame chemistry. Effects ofturbulent mixing on the reactionrates were also considered. The results show that thepresent KIVA/CHEMKIN model isable to simulate the ignition and combustion process in the HCCI engines. Thepredictive model has been developed by Miguel et al. (2009) using a Matlabenvironment from 269 observations that cover the full operation range of the engine inHCCI combustion mode. The development of a new heat-release rate model was used tosimulate the HCCI combustion mode for an engine fueled with EN590 fuel.

The simulation model for SI engine knock has been developed by Zhen et al..The model is based on a three-zone approach (i.e., unburned, burning, and burnedzones). Tanaka’s reduced chemical kinetic model for a commercial gasoline fuel withan RON of 95 has been modified and applied in both burned and unburned zonesincorporated with the LUCKS (Loughborough University Chemical KineticsSimulation) code.It has been concluded that a numerical simulation has been widelyused as a good simulation and a powerful tool to investigate HCCI and todevelopcontrol strategies for HCCI because of its greater flexibility and lower costcompared with engine experiments.

PREVIOUS ENGINE MODIFICATION

Recently, there have been several experimental investigations using modified dieselengine operating in HCCI. Although the engine specifications are different, ideas can begenerated. In the recent study, a homogeneous mixture of fuel and air was prepared byusing a diesel fuel vaporizer (Ganesh and Nagarajan, 2010). The diesel vapor providedby this device forms a very light and dispersed aerosol, where due to their sizes, thedroplets lose their momentum a short distance downstream of the nozzle (no walltargeting), follow the air motion very well, have very fast evaporation due to very highsurface to volume ratio, and disperse very uniformly in the surrounding air stream. Allthe properties of this ‘‘gas-like’’ aerosol make it ideally suitable for external dieselmixture preparation, with the creation of a highly disperse and homogeneous mixture,minimal wall-wetting and very fast evaporation during the compression stroke. Fig.8shows the diagram of a vaporized fuel leaving the vaporizer into ambient conditions.

Miguel et al. (2009) has modified diesel engine to adapt it to HCCI combustionas shown in Fig. 9. First modification, the injection pump was extracted out of theengine block, and its design was modified to control the injection point. The gear of thecrankshaft coupling to the injection pump was substituted by a transmission belt.Second modification, an EGR system was designed, including an exhaust gasrefrigeration system. With this system the EGR by-passed mass fraction and thetemperature of the recirculated gases can be controlled. Xing et al. (2005) has modifieda four-cylinder, four-stroke high-speed DI diesel engine was employed as prototypeengine. One cylinder of the prototype engine was reformed for operating with HCCIcombustion, the others was running with original DI diesel engine. The experimentalsystem is shown in Fig. 10. In order to achieve proper HCCI combustion in the test-cylinder, some modifications were conducted on the prototype engine such as; theintake and exhaust system, injection system and external EGR system.

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Figure 8: Experimental modification (Ganesh and Nagarajan, 2010)

Figure 9: Experimental modification (Miguel et al., 2009)

To summarize there has been most of the experimental testing undertakenattempt to convert the diesel engine to HCCI mode using external mixture formationrather than internal mixture formation. The reason is due to minor modification as wellas proper mixture preparation. This mean the premixed hydrogen and air will beinjected at the intake manifold. As the induction mode takes place the mixture hydrogenand air will be charged into cylinder. Then compression process generated, it will ignitethe mixture of hydrogen and air as the pressure increase. The droplet of diesel then willbe injected. Not only oxygen assists the combustion process but also hydrogen speed upthe combustion and shortens the ignition delay. Theoretically, hydrogen will havesufficient time to break the molecular bond and consequently enhance the combustionprocess.

1.surge tank2.cooled EGR3.charge amplifier4.exhaust gas analyser5.computer6. dynamometer7.fuel tank8. CA encoder9. fuelvapouriser10.injection pump11.ECU12.fuel injector

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However, there is backfireusing external formation when hydrogen is injectedaway from the intake manifold since hydrogen has low ignition energy. For thisreason,the hydrogen injector will be located at the intake manifold (close to intakeport). In addition to the operation of the test engine, an efficient safety measure foroperating theengine need to be developed.

THERMODYNAMIC MODELING ANALYSIS

Combustion in a reciprocating internal combustion engine is often analyzed using a heatrelease approach. In this approach, the conversion of chemical energy into thermalenergy is modeled as heat. In essence by applying first law thermodynamics as shown inFig. 11(Ferguson, 1986).The equation can be defined as follow:

WQU (1)

.

11 hmddV

pddQ

ddm

uddu

m

(2)

Where

1m is the instantaneous leakage or blowby mass flow rate (kg/s), 1h is theenthalpy of the blowby masses (kJ/kg), u is the specific internal energy (kJ/kg), Q isthe heat transfer (kJ/kg), p is the pressure (N/m2) ,V is the volume (m3) , is the crankangle (degrees) and = engine speed (rev/s)

Figure 10: Experimental modification (Xing et al., 2005)

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For the present study, a zero-dimensional combustion model is employed. Thecombustion chamber is divided into two zones consisting of unburned gas (mixture offuel, air and residuals) and burned gas (mixture of 14 product species), each underuniform composition. This model assumes that at any instant of time during thecombustion with respect to crank angle as shown detail in appendix.

SOLUTION PROCEDURE

It can be seen from equation (1) that all terms had been investigated and the only termleft is the work term. The work done by the piston is equal to the product of pressureand the volume change with respect to crank angle. Solving the last term will give theoutput of pressure, temperature of burned gas, temperature of unburned gas, work done,heat loss and the enthalpy loss change with respect to crank angle

ub TTPfddP ,,,1

(3)

ubb TTPf

ddT

,,,2 (4)

ubu TTPf

d

dT,,,3

(5)

PfddW

,4 (6)

ubl TTPf

ddQ ,,,5

(7)

ubl TTPf

d

dH,,,6

(8)

Properties of diesel and hydrogen fuels are determined at the beginning of thecycle. Fuel properties of both fuels are given in Table 2.If the properties of diesel andhydrogen are known, properties of diesel and hydrogen are calculated as follows(assumes the mixtures in liquid volume fraction).

Figure 11: Thermodynamic Modeling

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2

1

)(i

iiVX (9)

iVi

sciVisdf X

AFXAF

/)/( (10)

which

i=1,2 1=diesel 2=hydrogen

density of total dual fuel (kg/m3)i density of given component in dual fuel

iVX )( volume fraction of given in dual fuel , (by volume percentage)sdfAF )/( stoichiometric fuel air ratio of dual fuel

scAF )/( stoichiometric fuel air ratio of given component

Table 2: Diesel and hydrogen fuels properties

Property Diesel hydrogenDensity (kg/m3) 850 0.09Molecular formula C10H22 H2Molecular weight(kg/kmol) 142.3 2.01Stoichiometric fuel-air ratio 0.0777 0.0293

FORMATION OF EQUATIONS OF COMBUSTION THERMODYNAMICS

The mixture is a dual fuel of composition diesel (C H O N) and hydrogen. Consideringthat there are 10 constituents the combustion reaction since the dissociation of O, H, OHand NO occurred.

NOvOHvOvHvHvCOvOvNv

OHvCOvNOyHNOHCx

109872652423

2221222 79.021.0

(11)

Where N is the total number moles, now by definition and conservation of mass:

10

11 01

i

y (12)

is the the number of C atoms, is the number of H atoms,is number of Oatoms,is number of N atoms, x is percentage of diesel in diesel–hydrogen fuelblend, y is percentage of hydrogen in diesel–hydrogen fuel blend,is fuel–airequivalence ratio,is stoichiometric molar fuel–air ratio, iv is coefficient describingproduct composition of i-th species, iy is mole fraction of i-th species, K is equilibriumconstant, T is temperature in K, P is pressure in bar.With the variation in the inputparameters various results and plots can be obtained using Matlab. The theoreticalmodeling will be compared to the results obtained from the experimental works.

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CONCLUSIONS

The effect of the amount of hydrogen addition on the fuel consumption and emission ofDI has been studied. Overall, the benefits of hydrogen are significant since these resultsshow that the diesel fuel with hydrogen additive can be further accomplished as there isplenty of room for continuous improvement on performances and emissions.

ACKNOWLEDGEMENT

The author would like to thank to Malaysia Government for fundingthe studies at theUniversity of Southern Queensland.

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NOMENCLATURE

BSFC brake specific fuel consumptionCA crank angleCFD computational fluid dynamicsCO carbon monoxideCR compression raioDI direct injectionEGR exhaust gas recirculationHC hydrocarbonHCCI homogenous charged compression ignitionNOx nitrogen monoxidePM particulate matterSI spark ignitionUHC unburnt hydrocarbonVCR variable compression raioVIT variable induction temperatureVVA variable valve actuation