A REVIEW ON METHODS OF HOMOGENEOUS CHARGE PREPARATION … · Int. J. Mech. Eng. & Rob. Res. 2015...

138

Int. J. Mech. Eng. & Rob. Res. 2015 Gowthaman S and Sathiyagnanam A P, 2015

A REVIEW ON METHODS OF HOMOGENEOUS

CHARGE PREPARATION FOR HCCI MODE ENGINE

Gowthaman S1* and Sathiyagnanam A P1

*Corresponding Author: Gowthaman S, � [email protected]

Homogeneous charge compression ignition (HCCI) engine has ultra low oxides of nitrogen (NOx)and particulate matter (PM) emissions with significant improvement in brake thermal efficiency.There is many issues still need to be solved for the efficient operation of HCCI mode engine.The homogeneous air- fuel mixture preparation is the one of the primary issue to operate theHCCI mode engine. The HCCI engine uses lean homogeneous air-fuel mixture, the performanceand emission characteristics of HCCI mode engine can be determined by percentage of air-fuelcharge convert to homogeneous form before the start of combustion process. Therefore,percentage of homogeneous charge is only parameter to improve the performance and reducethe exhaust emissions from the HCCI engine. Many researchers have been trying to improvethe HCCI engine operation with improve the percentage of homogeneous charge. This paperbriefly discussed possibilities and methods of homogenous charge preparation in HCCI engineand discussed the merits and demerits of homogeneous charge preparation methods used bythe researchers. And also reviews the impact of homogeneous air-fuel mixture on the HCCIengine performance and emission characteristics.

Keywords: Homogeneous charge compression ignition engine, Homogeneous chargepreparation methods, External mixture preparation, In cylinder mixture preparation

INTRODUCTION

Homogeneously charged compression ignition(HCCI) is a promising engine combustionmethod between spark ignition (SI) andcompression ignition (CI) Engines. HCCIcombustion is a multipoint lean premixed auto-ignition process with no discernable flamepropagation. In general, HCCI is largely

ISSN 2278 – 0149 www.ijmerr.com

Vol. 4, No. 2, April 2015

© 2015 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2015

1 Department of Mechanical Engineering, Annamalai University, Tamilnadu, India.

Research Paper

controlled by chemical kinetics and lessimpacted by fluid dynamics (Thring R, 1989).As the HCCI engine has a nearlyhomogeneous charge, soot is significantlyreduced, and NOx formation is relatively lowcompared to the CI engines (Ryan T W andCallahan T J, 1996). However, unburnedhydrocarbon and carbon monoxide levels in

139


HCCI are found to be higher than those in SIengines (Stanglmaier R H and Roberts C E,1999). Despite the many advantageousfeatures of HCCI combustion, difficulty inhomogeneous charge preparation is the mainissue to be resolved. Various homogeneouscharge preparation of HCCI engines are beingresearched, such as port fuel injection (PFI),early direct injection (EDI) and late directinjection (Gray III A W and Ryan III T W, 1997;Stanglmaier R H and Roberts C E, 1999;Harada A et al., 1998). These schemesmanipulate intake mixture properties;including inlet temperature (Tinlet), pressure(Pinlet), equivalence ratio (/) and exhaust gasre-circulation (EGR), so that auto-ignitionoccurs near the top dead center (TDC). Engineperformances are found to be best when theSOC falls between 5 and 15 crank angledegrees (CAD) after TDC (Akhilendra P S andAgarwal A K, 2012; and Peng Z et al., 2005).

The start of combustion process is typicallycontrolled by the air- fuel mixture. If the HCCIengine is using well mixed air-fuel charge,reduced the ignition delay period of the chargeand combustion starts earlier with lesscombustion duration (Nathan S S et al., 2010).Therefore, well premixed air-fuel charge canincrease the power output and reduce theemissions of PM, CO and NOx emissions.However if the HCCI engine operates withinhomogeneous charge, it shows the highersoot and HC emissions in the engine exhaust(Duc P M andWattanavichien K, 2007).

The rate of preparation of homogeneouscharge can varied with inlet air temperature,air swirl, fuel properties, equivalence ratio andinjector properties. Many researchers havebeen used all these methods to improve the

rate of homogeneous mixture. While using highoctane number fuels or duel fuel mode,enhance the air-fuel mixture as homogeneousform, it improve the engine power output. dieselwith biogas fuelled HCCI engine hasinvestigated by Ramesh et al. (Mohamed I Mand Ramesh A, 2013). Here author used inletair charge to create and improve thehomogeneous mixture before the combustiontake place. If increased the inlet air temperaturecan be vaporised the fuel within a short timeof period between the fuel injection andcombustion start. The rate of increasing theinlet air temperature should be limited,because higher inlet air temperature havebeen reduced the volumetric efficiency of theengine and reduced the engine power.

Intake air pressure boosting is a commonway to improve the engine output power whichis widely used in the high performance SI andCI engines applications. The effect of intakeair pressure on the combustion characteristicsand exhaust emissions of homogeneouscharge compression ignition engine (MustafaCanakci, 2012). The intake air is pressurizedby using supercharger and turbocharger duringsuction stroke. The high pressurized inlet aircan create the swirl inside the cylinder, and itenhances the vaporization of fuel and createshomogeneous mixture before the combustionstart.

The fuel properties can governing thehomogeneous charge preparation, the fuelviscosity and latent heat of vaporisation areplay major roll for the homogeneous chargepreparation (Iida N, 1997). The high viscosityfuels difficult to atomise and need more timeto vaporise and form homogeneous mixture.Starck et al. (Starck L et al., 2010) investigated

140


impact of fuel characteristics on HCCIcombustion, performance and emissions. Heconcluded that a fuel having low cetane numberand high volatility could improve the HCCIoperating range of more than 30%. This paperis dedicated to review how the air-fuel mixtureis created as homogeneous form and methodswhich are used in the HCCI engine for preparethe homogeneous mixture. Here also bediscussed the merits and demerits of thesemethods and impact on HCCI engineperformance and emissions.

HCCI ENGINE PRINCIPLE

HCCI is an alternative piston-engine combustionprocess that can provide efficiencies as high ascompression-ignition, direct-injection (CIDI)engines (an advanced version of the commonlyknown diesel engine) while, unlike CIDI engines,producing ultra-low oxides of nitrogen (NOx) andparticulate matter (PM) emissions (Dae Sik KimandChang Sik Lee, 2006). HCCI enginesoperate on the principle of having a dilute,premixed charge that reacts and burnsvolumetrically throughout the cylinder as it iscompressed by the piston. In some regards,HCCI incorporates the best features of both

spark ignition (SI) and compression ignition(CI), as shown in Figure 1. As in an SI engine,the charge is well mixed, which minimizesparticulate emissions, and as in a CIDI engine,the charge is compression ignited and has nothrottling losses, which leads to high efficiency.However, unlike either of these conventionalengines, the combustion occurs simultaneouslythroughout the volume rather than in a flamefront. This important attribute of HCCI allowscombustion to occur at much lowertemperatures, dramatically reducing engine-out emissions of NOx (Suzuki H et al., 1997).Most engines employing HCCI to date havedual mode combustion systems in whichtraditional SI or CI combustion is used foroperating conditions where HCCI operation ismore difficult. Typically, the engine is cold-started as an SI or CIDI engine, then switchedto HCCI mode for idle and low- to mid-loadoperation to obtain the benefits of HCCI in thisregime, which comprises a large portion oftypical automotive driving cycles. For high-loadoperation, the engine would again be switchedto SI or CIDI operation (Suzuki H et al., 1997).Research efforts are underway to extend therange of HCCI operations.

Figure 1: Schematic Diagram of SI, CI and HCCI (26)

141


HOMOGENEOUS CHARGE

PREPARATION

In diesel HCCI combustion, it is difficult toprepare homogeneous mixture because of thelower volatility, higher viscosity and lowerresistance to auto-ignition of diesel fuel. First,elevated temperatures are required beforesignificant vaporization occurs, making iteasier to form a premixed homogeneouscharge. Second, diesel fuel has significantcool-combustion chemistry, leading to rapidauto-ignition once compression temperaturesexceed about 800 K (Suzuki H et al., 1998).This can lead to overly advanced combustionphasing and high combustion rates.Accordingly, the essential factor needed toachieve diesel HCCI combustion is mixturecontrol, including both charge components andtemperature control in the whole combustionhistory and high pre-ignition mixing rates.

HOMOGENEOUS CHARGE

PREPARATION STRATEGIES

The HCCI engine have the difficulties in thepreparation of the homogeneous mixture,difficulties in control of the starting phases ofcombustion and control of the combustion rate,high hydrocarbon and CO emissions, anddifficulties in extension of the load range. Thestrategies for mixture preparation are eitherin cylinder direct injection or external mixture

preparation. Both the preparation methodshave their own disadvantages that the externalmixture has a low volumetric efficiency and in-cylinder mixture is prone to an oil dilution. Thissession describes the strategies andimplementations of mixture preparation.

Premixed/Direct-injected HCCICombustion

In premixed/direct-injected HCCI combustion,port injection was chosen for the main fuelsupply to create a homogeneous charge, anddirect fuel injection into the cylinder was usedto change the concentration and position oflocal fuel-rich regions with the purpose ofcontrolling HCCI combustion. A homogeneouscharge compression ignition dieselcombustion (HCDC) system, which is theearliest premixed/direct-injected HCCIcombustion, has been proposed by Odaka etal. (Odaka M et al., 1999; Midlam-Mohler S etal., 2003; Guezennec Y et al., 2002; Midlam-Mohler S, 2004). In their system, most of thefuel was injected into the intake manifold toform a homogeneous pre-mixture in thecombustion chamber and the premixture wasignited with a small amount of fuel directlyinjected into the cylinder. This system canreduce both NOx and smoke emissions betterthan ordinary diesel engines. Smoke isreduced near-uniformly as the premixed fuelratio is increased.

Figure 2: Strategies for Early DI Mixture Preparation

142


Midlam-Mohler et al. (Aroonsrisopon T etal., xxxx; Berntsson A W and Denbratt I, 2004;Inagaki K and Fuyuto T, 2006) have alsodeveloped a premixed/direct-injected HCCIsystem. Port/manifold fuel injection is achievedusing a low pressure atomizer system anddirect injection is achieved using a highpressure injection system. The atomizersystem delivers fuel as a premixed leanhomogeneous mixture into the cylinder. At lowloads, the main torque is from thehomogeneous charge fuel and the directinjection fuel is mainly for ignition; at high loads,the maximum homogeneous charge fuel isused and direct injection fuelling is increasedto full load. Small droplet size (<1 mm meandiameter) allows rapid evaporation during thecompression stroke, removing the need forintake air heating. The results indicated thatIMEP can be up to 4.7 bar by varying intakeconditions in the speed range from 1600 to3200 rpm. Furthermore, the mixed-modeHCCI combustion can achieve very low NOxand smoke emissions, less than 4 ppm and0.02 FSN respectively.

Foster et al. (Panão M R O and Moreira A LN, 2007) presented results pertaining toexpanding HCCI operations by chargestratification achieved by both port and directfuel injection. The stratification of the chargewas altered in two ways, (a) by altering the ratioof direct injected fuel to fuel supplied to theintake system and (b) by retarding the injectiontiming of the DI injector. Stratified chargeshows potential as a viable enhancement forHCCI combustion at the lean limit. Thecombustion becomes more stable with morestratified charge. Berntsson and Denbratt(Saxena Samveg, Schneider Silvan, Aceves

Salvador, Dibble Robert et al., 2012) alsoinvestigated the control of HCCI combustionusing premixed/ directed-fuel injection. In theirexperiments, port injection was used for themain fuel supply to create a homogenous air–fuel mixture. Engine experiments in both opticaland traditional single cylinder engines werecarried out with PRF50 as fuel. The amount ofstratification as well as injection timing of thestratified charge was varied. The maximumrate of heat release depends on the amountof stratification – a larger amount gives a lowerrate of heat release but the main heat releaseis advanced. Varied injection timing results indifferent phasing of the main heat release. Theuse of charge stratification for HCCIcombustion can lead to a wider operatingrange, due to its effect on combustion phasingand rate of heat release. Increasing thestratification amount or late injection timing ofthe stratified charge can lead to an advancedCA50 timing and higher NOx emissions.

In the research mentioned above, the directinjected fuel is the same as the premixed fuel.In premixed/direct-injected HCCI combustion,these two fuels can also be different, and fuelcharacteristics can also be used to controlcombustion. In the system developed byInagaki et al. (Kelly-Zion P L and Dec J E,2003)., gasoline was supplied to the intake airport and diesel fuel was injected directly intothe engine cylinder to act as an ignition triggerat timing before TDC. It was found that theignition phasing of combustion can becontrolled by changing the ratios of the twoinjected fuels, such that combustion proceedsvery mildly. Spatial stratification of ignitabilityin the cylinder prevents the entire mixture fromigniting instantaneously. The operable load

143


range, where NOx and smoke emissions wereless than 10 ppm and 0.1 FSN respectively,was extended up to an IMEP of 12 bar usingan intake air boosting system together withdual fuelling.

Early Direct Injection HCCI

Because of the disadvantage of port fuelinjection, an early direct injection approachtowards achieving diesel-fuelled HCCI hasbeen investigated. Compared with premixingin the intake port, this approach offers threepotential advantages (Zhao F et al., 2003). 1)By injecting the fuel in the compression stroke,the higher in-cylinder temperatures anddensities can help vaporize the diesel fuel andpromote mixing. This allows cooler intaketemperatures, reducing the propensity for earlyignition. 2) With a carefully designed fuelinjectors, the possibility exists to minimize fuelwall wetting that can cause combustioninefficiency and oil dilution. 3) In principle, onlyone fuelling system is required for both HCCIand conventional diesel operation. The maindisadvantage of early DI for HCCI is that it iseasy to produce wall wetting due to over-penetration of the fuel. Finally, it should be notedthat controlling combustion phasing is still acritical issue for early-DI HCCI becauseinjection timing does not provide an effectivemeans of directly controlling combustionphasing as in conventional diesel combustion.Several different methods of early-DI HCCIhave been investigated, including dual-injectiontechniques that combine early-DI HCCI with aconventional diesel Injection. Manycombustion systems of early direct injectionHCCI have been developed such as PREDIC(premixed lean diesel combustion)/MULDIC(multiple stage diesel combustion), UNIBUS

and MULINBUMP, are shown in Figure 2 whichare reviewed next.

PREDIC

One of the more significant efforts in early-DIHCCI is the work conducted at the New ACEInstitute in Japan. Initial reports of this work byTakeda et al. (1996)and Nakagome et al.(1997) discussed various fuel injectionstrategies and results show that it is possibleto achieve very low NOx and smoke emissionswith this technique. However, similar to diesel-fuelled HCCI with port fuel injection, HCemissions were high and fuel consumption wassignificantly increased over conventional dieselcombustion due to poor combustion efficiencyand overly advanced combustion phasing. Tominimize the over-penetration and wall wettingthat can occur when fuel is injected well beforeTDC, when in-cylinder air densities andtemperatures are low, three injectors wereused in their study (one at the centre, and twoon the sides) to control the injection timing andquantity of each injector independently. Thedouble injectors mounted on either side of thecylinder, each with two sprays, were positionedso that the fuel sprays would collide in themiddle of the chamber to limit wall wetting withvery early injection. In addition, the nozzle holediameter of the centre injector was reducedfrom 0.17 mm to 0.08 mm.

The number of holes was also increasedfrom 6 to 16 and some tests were carried outusing a centre injector with 30 holes at variousangles. Using this injection method, the enginecould be operated with PREDIC. To overcomesignificant over-advanced combustion, specialfuel blends with cetane numbers of 19 and 40were developed and tested, along withchanges in the intake temperature and

144


compression ratio. A subsequent study(Harada A et al., 1998) reported thedevelopment of a swirling-flow pintle-nozzleinjector that produces a more uniform mixtureand reduces wall wetting (as measured byreduced lube-oil dilution), thereby improvingcombustion efficiency.

In an attempt to achieve higher powerdensities, this early-DI work was expanded toinclude a second fuel injection near TDC(Hashizume T et al., 1998). This wasaccomplished by using the dual side-mounted,impinging-spray injectors to produce the leanpremixed charge, whilst a centre-mountedinjector was used to inject additional fuel nearTDC. Approximately half of the fuel was injectedin each stage, which was near the maximumamount of premixed fuel that could be usedwithout causing knock. Various combinationsof injection timings (for both stages) and fuelCN were used to optimize performance andemissions. Since the second stage burnssimilarly to conventional diesel combustion,NOx and PM emissions were much higher withthis approach than those obtained with pureHCCI.

However, NOx was reduced to about halfthat of conventional diesel combustion withouta significant increase in fuel consumption.Smoke emissions also decreased, but HCemissions were higher. In order to solve theproblem of high HC and CO emissions duringHCCI operation, Akagawa H et al. (1999)investigated the effects of EGR rate andoxygenated fuels on fuel consumption and theeffects of the top-land crevice volume on HCand CO emissions and on adhesion of fuel onthe walls. They also investigated doubleinjections, the first earlier injection to form a

homogeneous and lean mixture, and thesecond later one for conventional combustion.Much higher loads were found possible whilstachieving low NOx emissions but this wasaccompanied by an increase in fuelconsumption. Multiple injections were alsoinvestigated by Morita et al. (2000) and furtherdeveloped by Nishijima et al. (2002),investigating the effects of split injections andwater injection. Split injections reduced HC andCO emissions but unfortunately increasedNOx emissions.

UNIBUS

Yanagihara H (2001) have also applied HCCIcombustion with diesel fuel (Toyota UNIBUS).As described by Yanagihara, the engineoperates in UNIBUS mode up to about half loadand half speed. As with other DI HCCItechniques, mixture preparation is a key issue.Yanagihara et al. used piezo-actuator injectorswith pintle type injector nozzles to reduce thespray penetration in an attempt to limit the over-leaning of the charge. The technique involvesa combination of an early injection (around 50ºBTDC) and a late injection (about 13º ATDC).The majority of data presented in the paperwere taken with 12:1 compression ratio,presumably to avoid overly advancedcombustion of the premixed fuel. Theinvestigations examined the impact of theinjection timing, level of fuelling, EGR rate anddouble injections on emissions, torque,instantaneous heat release and load. Theseresults were compared with conventionaldiesel combustion with the same injector. Lowlevels of fuelling and low injection pressureswere thought to be most appropriate to limitwall wetting and knocking with this particular

145


injector nozzle.

A luminous flame is not observed, due tothe negligible PM available for oxidation, andconfirmed by low PM emissions. The use ofEGR is also discussed, and a 60% EGR levelis shown to be effective for delaying the HCCIcombustion by about 7deg crank angle. A dual-injection strategy has also been developed,with 50% of the fuel introduced in a secondinjection at 13º ATDC. The second injectionsignificantly improves the combustionefficiency of the early-injected fuel, reducingHC emissions from 5000 ppm to 2000 ppmand CO emissions from about 8000 ppm to2000 ppm (Hasegawa R and Yanagihara H,2003). Therefore, fuel combustion from thesecond injection can be considered as atrigger for a portion of the heat release fromthe early-injected fuel. Although the secondinjection increases NOx emissions above thenear-zero levels for early injection alone, they

are still very low for a diesel engine. Furtherstudies (Najt P E and Foster D E, 1983) werethen carried out looking at the possibility ofusing a second injection closer to TDC totrigger the combustion, which reduced the NOxbenefits but also the fuel consumption penalty.

MULINBUMP

Su et al. (et al., 2003; 2004; 2005) proposeda compound diesel HCCI combustion system– MULINBUMP, combining premixedcombustion with ‘‘lean diffusion combustion’’.The premixed combustion was achieved bythe technology of multi-pulse fuel injection. Thestart of pulse injection, injection pulse number,injection period of each pulse and the dwelltime between the injection pulses werecontrolled. The objective of controlling the pulseinjection was to limit the spray penetration ofthe pulse injection so that the fuel will notimpinge on the cylinder liner, and to enhance

Figure 3: UNIBUS Combustion Strategy

146


the mixing rate of each fuel parcel. The last ormain injection pulse was set around TDC. Aflash mixing technology was developed fromthe development of a so-called BUMPcombustion chamber, which was designed withsome special bump rings. The combustion offuel injected in the main injection proceeds atmuch higher air/fuel mixing rate than in aconventional DI diesel engine under the effectof the BUMP combustion chamber, whichleads to ‘‘lean diffusion combustion’’.

The characteristics of auto-ignition and rateof heat release of the premixed fuel of multi-pulse injection were investigated, being oneof the more important aspects that affectengine emissions. By advancing the starttiming of multi-pulse injection, noisy auto-ignition can be avoided, but over-advancingof the start timing will lead to over-mixing,resulting in higher total hydrocarbon (THC)emissions. The results also show that in thecompound combustion mode, the fuelproportion of multi-pulse injection should be

high, under the condition of no noisy autoignition, which is helpful in the reduction of NOxemissions. Small amounts of fuel in multi-pulseinjection offer no benefits to NOx emissionsreduction, but worsen smoke emissions.

Compound combustion technology haspotential in realizing HCCI combustion atrather wide operating conditions of a dieselengine. The basic idea of the MULINBUMPcompound combustion system is: 1) at lowloads of a diesel engine, there is control of theHCCI combustion process by the multi-pulsefuel injection strategy, which can achieve verylow NOx and PM emissions (<10 ppm); and2) at medium and high loads, the strategy ofcombining premixed combustion with ‘‘leandiffusion combustion’’ is applied. The mixingrate of fuel and air is improved by combininga high mixing rate combustion chamber with asuper high injection pressure, thus achievingrapid mixing. Over the full load range of a dieselengine, the best injection modes can beobtained at different conditions by controlling

Figure 4: Multi-pulse Injection of MULINBUMP

147


multi-pulse injection, thereby clean and highefficiency combustion of the diesel engine canbe achieved over the full load range. To date,the IMEP of compound combustion hasreached 0.93 MPa.

Narrow Angle Diesel Injection

A narrowing of the spray cone angle iscommonly used to reduce the fuel wetting onthe piston head surface and cylinder wall. Theuse of a narrow fuel injector nozzle spray coneangle to avoid spray–wall interactions at theearly injection timings shows promise forachieving HCCI combustion while maintaininga relatively high efficiency (Walter B andGatellier B; 2003; Shimazaki N et al., 2003;Mueller C J et al., 2004; Duret P et al., 2004).In the research of Kim and Lee (2007), twoinjector nozzles with different spray coneangles (156 deg and 60 deg) were used toexamine the potential of HCCI combustion.The compression ratio of the test engine wasreduced from 17.8:1 to 15:1 to prevent theimmoderately advanced ignition of the pre-mixture formed by early injection. The resultsshowed that in the case of the conventionaldiesel engine, the IMEP was decreasedrapidly as the injection timings were advancedbeyond 20º BTDC and indicated specific fuelconsumption (ISFC) were also deteriorated.In the case of advanced injection timingbetween 30ºand 50º before the TDC, the IMEPwas approximately half of that attained underthe conventional diesel combustion with theinjection timing near the TDC. Injecting the fuelat very early timing helps to create HCCIcombustion. However, injecting too early leadsto poor fuel evaporation and piston bowl spraytargeting issues. At that condition, the fuel–airmixture is formed at the outside of the

combustion chamber and the deterioratedcombustion efficiency can be expected.Moreover, due to the shifting of combustionevent to earlier side, this causes the increaseof negative work during compression stroke.

These trends are regarded as typicalproblems of early injection HCCI engine thatlower the thermal efficiency and increase theincomplete combustion products such as theHC and CO emissions. In contrast, the ISFCindicated a modest decrease in the IMEPalthough the injection timing was advanced to50–60º BTDC in the case of a narrow sprayangle configuration. This reveals that thenarrow angle concept was effective inmaintaining the high ISFC and IMEP when thefuel was injected at an early timing for HCCIcombustion. In addition, the IFP has developeda combustion system able to reach near-zeroparticulate and NOx emissions whilemaintaining performance standards of the DIDiesel engines, especially in terms of outputpower and torque. This dual mode engineapplication called NADI (narrow angle directinjection) applies homogeneous chargecompression ignition at part load and switchesto conventional Diesel combustion to reachhigh and full load requirements. Therefore, itcan be concluded that the narrow spray coneangle injector can reduce the wall wettingproblem and avoid an out of bowl injectionwhen the fuel was injected at an early timingfor HCCI combustion.

Late Direct Injection HCCI

One of the most successful late injection DIHCCI systems for achieving diesel-fuelledHCCI is the MK (modulated kinetics)combustion system developed by the Nissan

148


Motor Company. The principles of this lateinjection HCCI combustion process aredescribed by Kawashima et al. (1998) andKimura et al. (1999). In order to achieve thediluted homogeneous mixture required forHCCI, a long ignition delay and rapid mixingare required. The ignition delay is extendedby retarding the injection timing from 7ºBTDCto 3º ATDC and by using high levels of EGR,sufficient to reduce the oxygen concentrationto 15–16%. Rapid mixing was achieved bycombining high swirl with toroidal combustion-bowl geometry. The operating range for the firstgeneration MK system was limited to aboutone-third of peak torque and half speed. In theMK mode, NOx emissions were reducedsubstantially (to about 50 ppm) without anincrease in PM. Combustion noise was alsosignificantly reduced. In addition, it should benoted that with this late-DI HCCI technique,combustion phasing is controlled by injectiontiming, which is an advantage over port fuelinjection and early-DI HCCI techniques.

In the development of a second-generationsystem, several modifications were made toexpand the range of MK operation to higherloads and speeds (Kimura S et al., 2003).Since more fuel must be injected at higherloads, a high pressure common-rail fuel systemwas used to provide high injection pressuresat all speeds to reduce fuel injection duration.The ignition delay was increased by reducingthe compression ratio to 16:1 and adding EGRcooling to reduce the intake temperature (YapD et al., 2006). To minimize the potential forliquid fuel impingement on the piston bowl wall,the piston bowl diameter was increased from47 to 56 mm. This change significantly

reduced HC emissions under cold-engineconditions. The results show that the second-generation MK system can be used over theentire range of everyday driving, indicating thatthe engine met the second-generation targetsof about half load and three-quarters speed.NOx emissions are stated to be reduced by98% compared with conventional operationwithout EGR, whilst PM emissions are similarto the conventional engine.

More recent work by Kawamoto et al.(2004) proposed the use of higher CN fuel,which went against other HCCI operatingrequirements, but was recommended toreduce HC emissions under cold startconditions. The major advantage of the MKcombustion system is illustrated by its ease ofimplementation because it does not requireadditional or different hardware. Equally, itsoperation with conventional hardware did notaffect negatively the engine’s specific poweroutput. However, the injection timing retard andlower compression ratio lead to a deteriorationof cycle efficiency and higher unburned HCemissions.

CONCLUSION

Homogeneous charge compression ignitionengines have ultra low NOx and PM emissionswithout affect the engine efficiency. HoweverHCCI mode engines have some challengingissues to operate the HCCI mode engineefficiently. The preparation of homogeneouscharge is the one of the major problem in HCCIengine operation. In this review, discussed andconclude the methods which are used toprepare the homogeneous charge andanalysed the effect on HCCI engineperformance and emission parameters.

149


In port fuel injection, the fuel is injected onfresh inlet air at intake manifold. The fuel andair are having enough time to mix and formhomogeneous charge before take thecombustion process. It can be reduced bothNOx and particulate matters emissions. Theport injection method is also have the somedisadvantages due to the early injection themisfire may occur, it can be reduced enginepower output and increased HC and smokeemission.

The early direct injection method is used toovercome the disadvantage of port injectionmethod. The early DI method can increasedthe in cylinder temperature and reduced theignition delay. The main disadvantage of earlyDI for HCCI is that it is easy to produce wallwetting due to over-penetration of the fuel.Finally, it should be noted that controllingcombustion phasing is still a critical issue forearly-DI HCCI because injection timing doesnot provide an effective means of directlycontrolling combustion phasing as inconventional diesel combustion. Severaldifferent methods of early-DI HCCI have beeninvestigated, including dual-injectiontechniques that combine early-DI HCCI with aconventional diesel Injection. Manycombustion systems of early direct injectionHCCI have been developed such as PREDIC(premixed lean diesel combustion)/MULDIC(multiple stage diesel combustion), UNIBUSand MULINBUMP.

One of the most successful injection systemis late injection DI HCCI systems for achievingdiesel-fuelled engine. The principles of this lateinjection HCCI combustion process aredescribed by Kawashima et al. (1998) andKimura et al. (1999). In order to achieve the

diluted homogeneous mixture required forHCCI, a long ignition delay and rapid mixingare required. The ignition delay is extendedby retarding the injection timing from 7º BTDCto 3º ATDC and by using high levels of EGR,sufficient to reduce the oxygen concentrationto 15–16%. Rapid mixing was achieved bycombining high swirl with toroidal combustion-bowl geometry. The operating range for the firstgeneration MK system was limited to aboutone-third of peak torque and half speed. Inaddition, it should be noted that with this late-DI HCCI technique, combustion phasing iscontrolled by injection timing, which is anadvantage over port fuel injection and early-DIHCCI techniques.

REFERENCES

1. Akagawa H, Miyamoto T, Harada A,Sasaki S, Shimazaki N, Hakeshi T, et al.,(1999), “Approaches to Solve Problemsof The Premixed Lean DieselCombustion”, SAE Paper 1999-01-0183.

2. Akhilendra PS and Agarwal A K (2012),“Combustion Characteristics of DieselHCCI Engine: An ExperimentalInvestigation Using External MixtureFormation Technique”, Appl Energy, Vol.99, pp. 116-125.

3. Aroonsrisopon T, Werner P, Waldman JO, Sohm V, Foster D E, Morikawa T etal. (2004), “Expanding the HCCIOperation with the Charge Stratification”,SAE Paper.

4. Berntsson A W and Denbratt I (2004),“HCCI Combustion Using ChargeStratification for Combustion Control”,SAE paper 2007-01-0210.

150


5. Dae Sik Kim and Chang Sik Lee (2006),“Improved Emission Characteristics ofHCCI Engine by Various Premixed Fuelsand Cooled EGR”, Fuel, Vol. 85, pp. 695-704.

6. Duc P M and Wattanavichien K (2007),“Study on Biogas Pre mixed ChargeDiesel Dual Fuelled Engine”, EnergyConvers Manag., Vol. 48, pp. 2286-2308.

7. Duret P, Gatellier B, Monteiro L, MicheM, Zima P and Maroteaux D (2004),“Progress in Diesel HCCI CombustionWithin the European SPACE LIGHTProject”, SAE Paper 2004-01-1904.

8. Gray III A W and Ryan III T W (1997),“Homogeneous Charge CompressionIgnition (HCCI) of Diesel Fuel”, SAEpaper 971676.

9. Guezennec Y, Midlam-Mohler S andRizzoni G (2002), “A Mixed Mode HCCI/DI Engine Based on a Novel Heavy FuelAtomizer”, 8th Diesel Engine EmissionsReduction (DEER) Workshop.

10. Harada A, Shimazaki N, Sator, S,Miyamoto T, Akagawa H and TsujimuraK (1998), “The Effects of MixtureFormation on Premixed Lean DieselCombustion”, SAE Paper 980533.

11. Harada A, Shimazaki N, Sator, S,Miyamoto T, Akagawa H and TsujimuraK (1998), “The Effects of MixtureFormation on Premixed Lean DieselCombustion”, SAE paper 980533.

12. Hasegawa R and Yanagihara H (2003),“HCCI Combustion in DI Diesel Engine”,SAE Paper 2003-01-0745.

13. Hashizume T, Miyamato T, Akagawa Hand Tsujimura K (1998), “Combustion andEmission Characteristics of MultipleStage Diesel Combustion”, SAE Paper980505.

14. Iida N (1997), “Alternative Fuels andHomogeneous Charge CompressionIgnition Combustion Technology”,SAE972071.

15. Inagaki K and Fuyuto T (2006),“Combustion System with Premixture-Controlled Compression Ignition”, R&DRev Toyota CRDL, No. 3, pp. 35-46.

16. Kawamoto K, Araki T, Shinzawa M,Kimura S, Koide S and Shibuya M(2004), “Combination of CombustionConcept and Fuel Property for Ultra-cleanDI Diesel”, SAE Paper 2004-01-1868.

17. Kawashima J I, Ogawa H and Tsuru Y(1998), “Research on a Variable SwirlIntake Port for 4-valve High-speed DIDiesel Engines”, SAE Paper 982680.

18. Kelly-Zion P L and Dec J E (2000), “AComputational Study of the Effect of FuelType on Ignition Time in HomogeneousCharge Compression Ignition Engines”,Proc Combust Inst., Vol. 28, No. 1, pp.1187-1194.

19. Kim M Y and Lee C S (2007), “Effect of aNarrow Fuel Spray Angle and a DualInjection Configuration on TheImprovement of Exhaust Emissions in AHCCI Diesel Engine”, Fuel, Vol. 86, Nos.17–18, pp. 2871-2880.

20. Kimura S, Aoki O, Kitahara Y andAiyoshizawa E (2000), “Ultra-cleanCombustion Technology Combining a

151


Low-Temperature and PremixedCombustion Concept for Meeting FutureEmission Standards”, SAE Paper 2000-01-0200.

21. Kimura S, Aoki O, Ogawa H, MuranakaS and Enomoto Y (1999), “NewCombustion Concept for Ultra-clean andHigh-efficiency Small DI Diesel Engines”,SAE Paper 1999-01-3681.

22. Midlam-Mohler S (2004), “Diesel HCCIwith External Mixture Preparation”, 10thDiesel Engine Emissions Reduction(DEER) Workshop.

23. Midlam-Mohler S, Guezennec Y andRizzoni G (2003), “Mixed-mode DieselHCCI with External Mixture Formation:Preliminary Results”, 9th Diesel EngineEmissions Reduction (DDER)Workshop.

24. Mohamed I M and Ramesh A (2013),“Experimental Investigations on aHydrogen Diesel Homogeneous ChargeCompression Ignition Engine withExhaust gas Recirculation”, Int J HydrogEnergy Vol. 38, pp. 10116-10125.

25. Morita A, Iwashiro Y, Aoyagi Y andHashizume T (2000), “Observation of theDiesel Combustion Process in MultipleStage Injection”, in Proceedings Of Thiesel2000 Thermofluidynamic Processes InDiesel Engines, pp. 447-452.

26. Mueller C J, Martin G C, Briggs T E andDuffy K P (2004), “An ExperimentalInvestigation of in-cylinder Processes UnderDual-injection Conditions in a DI DieselEngine”, SAE Paper 2004-01-1843.

27. Mustafa Canakci, CombustionCharacteristics of a DI-HCCI gasolineengine Running at Different BoostPressure”, Fuel, Vol. 96, pp. 546-555.

28. Najt P E and Foster D E (1983),“Compression Ignited HomogeneousCharge Combustion”, SAE Paper830264.

29. Nakagome K, Shimazaki N, Miimura Kand Kobayashi S (1997), “Combustionand Emissions Characteristics ofPremixed Lean Diesel CombustionEngine”, SAE Paper 970898.

30. Nathan S S,Mallikarjuna J M and RameshA (2010), “An Experimental Study of theBiogas-diesel HCCI Mode of Engineoperation”, Energy Convers Manag.,Vol. 51, pp. 1347-1353.

31. Nishijima Y, Asaumi Y and Aoyagi Y(2002), “Impingement Spray System WithDirect Water Injection for Premixed LeanDiesel Combustion Control”, SAE Paper2002-01- 0109.

32. Odaka M, Suzuki H, Koike N and Ishii H(1999), “Search for Optimizing Method ofHomogeneous Charge DieselCombustion”, SAE Paper 1999-01-0184.

33. Panão M R O and Moreira A L N (2007),“Interpreting the Influence of Fuel SprayImpact on Mixture Preparation for HCCICombustion with Port–fuel Injection”,Proc Combust Inst., No. 31, pp. 2205-2213.

34. Peng Z, Zhao H, Tom and LadommatosN (2005), “Characteristics of Homogeneous

152


Charge Compression Ignition (HCCI)Combustion and Emissions of n-heptane”, Comb Sci Tech 2005, Vol. 177,No. 11, pp. 2113-2150.

35. Ryan T W and Callahan T J (1996),“Homogeneous Charge CompressionIgnition of Diesel Fuel”, SAE Paper961160.

36. Saxena Samveg,Schneider Silvan,Aceves Salvador and Dibble Robert(2012), Wet Ethanol in HCCI Engineswith Exhaust Heat Recovery to Improvethe Energy Balance of Ethanol Fuels”,Appl Energy, Vol. 98, pp. 448-457.

37. Shimazaki N, Tsurushima T andNishimura T (2003), “Dual ModeCombustion Concept With PremixedDiesel Combustion By Direct InjectionNear Top Dead Center”, SAE paper2003-01-0742.

38. Stanglmaier R H and Roberts C E (1999),“Homogeneous Charge CompressionIgnition (HCCI) Benefits, Compromisesand Future Engine Applications”, SAEPaper 1999-01- 3682.

39. Stanglmaier R H and Roberts C E (1999),“Homogeneous Charge CompressionIgnition (HCCI): Benefits, Compromise,and Future Engine Applications”, SAEPaper 01-3682.

40. Starck L, Lecointe B, Forti L and JeulandN (2010), “Impact of Fuel Characteristicson HCCI Combustion Performance andEmissions”, Fuel, Vol. 89, pp. 3096-3077.

41. Su W H, Lin T J and Pei Y Q (2003), “ACompound Technology for HCCI

Combustion in a DI Diesel Engine Basedon the Multi-pulse Injection and the BUMPCombustion Chamber”, SAE Paper2003-01-0741.

42. Su W H, Wang H and Liu B (2005),“Injection Mode Modulation for HCCIDiesel Combustion”, SAE Paper 2005-01-0117.

43. Su W H, Zhang X Y and Lin T J (2004),“Study of Pulse Spray, Heat Release,Emissions and Efficiencies in aCompound Diesel HCCI CombustionEngine”, in Proceedings of ASME-iceASME Internal Combustion EngineDivision, Fall Technical Conference,ICEF2004–927.

44. Suzuki H, Koike N and Odaka M (1997),“Exhaust Purification of Diesel EnginesBy Homogeneous Charge WithCompression Ignition. Part 1:Experimental Investigation OfCombustion And Exhaust EmissionBehavior Under Pre-mixedHomogeneous Charge CompressionIgnition Method”, SAE Paper 970313.

45. Suzuki H, Koike N and Odaka M (1997),“Exhaust Purification of Diesel EnginesBy Homogeneous Charge WithCompression Ignition. Part 2: Analysis ofCombustion Phenomena And NoxFormation By Numerical Simulation WithExperiment”, SAE Paper 970315.

46. Suzuki H, Koike N and Odaka M (1998),“Combustion Control Method ofHomogeneous Charge Diesel Engines”,SAE Paper 980509.

47. Takeda Y, Keiichi N and Keiichi N (1996),

153


“Emission Characteristics of Premixedlean Diesel Combustion with ExtremelyEarly Staged Fuel Injection”, SAE Paper961163.

48. Thring R (1989), “Homogeneous ChargeCompression Ignition (HCCI) Engines”,SAE Paper 8902068.

49. Walter B and Gatellier B (2003), “NearZero NOx Emissions and High FuelEfficiency Diesel Combustion: TheNADITM Concept Using Dual ModeCombustion”, Oil Gas Sci Technol., Vol.58, No. 1, pp. 101-114.

50. Yanagihara H (2001), “Ignition Timing

Controlat Toyota ‘‘UNIBUS’’ CombustionSystem”, in Proceedings of the IFPInternational Congress, pp. 35-42.

51. Yap D, Peucheret S M, Megaritis A,Wyszynski M L and Xu H (2006), “Naturalgas HCCI Engine Operation With ExhaustGas Fuel Reforming”, Int J HydrogenEnergy, Vol. 31, pp. 587-595.

52. Zhao F, Asmus T W, Assanis D N, Dec JE, Eng J A and Najt P M (2003),“Homogenous Charge CompressionIgnition (HCCI) Engine: Key Researchand Development Issues”, Warrendale,PA: Society of Automotive Engineers,pp. 150-154.

A REVIEW ON METHODS OF HOMOGENEOUS CHARGE PREPARATION … · Int. J. Mech. Eng. & Rob. Res. 2015...

Documents

Transcript of A REVIEW ON METHODS OF HOMOGENEOUS CHARGE PREPARATION … · Int. J. Mech. Eng. & Rob. Res. 2015...