异辛烷、乙醇及其混合燃料HCCI燃烧的试验研究和分析

第25卷(2007)第5期内燃机学报Transactions of CSICEval.25(2007)No5Article ID:10000909(2007)05-041408254067Experimental Study and analysis on HCCI Combustionof Iso-Octane Ethanol and Their blendZHANG Chun-hua, Gnanam Gnanaprakash, Andrzej Sobiesiak(L. Automobile School, Changan University, Xi'an 710064, China;2. Department of Mechanical Engineering, University of Windsor, Windsor N9B 3P4, Canada)Abstract: This paper investigates homogeneous charge compression ignition( HCCI)combustion on a modifiedengine fuelled with iso-octane, ethanol and iso-octane-ethanol blend. The engine performances are evaluatedbased on in-cylinder measured pressure. The parameters studied include heat-release rate ( HRR), indicatemean effective pressure( IMEP)and indicated thermal efficiency. The experimental results demonstrate that theombustion for ethanol occurs ahead of that for iso-octane The addition of i8o-octane to ethanol retards the on-getof combustion and subsequently leads to a reduction of the IMEP and indicated thermal efficiency. For a particu-lar fuel, the combustion depends mainly on the intake charge temperature and any increase in the initial chargetemperature leads to advance in combustion. At lower charge temperatures and engine speeds, the fuel-air mixturesquality of is poor, resulting in a poor combustion. The indicated thermal efficiency is 30%to 43%,bet-ter than those of typical SI engines. The presence of pre-chamber is advantageous to stable HCCI operation. Operation with ultra lean mixture reduces engine-out NO, emissions significantly.Keywords: HCCI combustion: Iso-octane: Ethanol; Iso-octane-ethanol blendCLC number: TK401Document code: A异辛烷、乙醇及其混合燃料HCCI燃烧的试验研究和分析张春化12, Gnanam Gnanaprakash2, Andrzej Sobiesiak2(1.长安大学汽车学院,陕西西安710064;2温莎大学机械工程系,温莎NB3P4,加拿大)摘要:在一台改制的发动机上进行了异辛烷、乙醇及其混合燃料HCCI燃烧的研究。发动机性能用缸内压力评估,研究用的参数包括放热率、平均指示压力和热效率。试验结果表明,乙醇着火时刻早于异辛烷;在乙醇中加入异辛烷可以推迟着火,并导致平均指示压力和热效率的降低;对某种特定燃料,HCCI燃烧的发生主要取决于进气充量温度,初始充量温度的增加将导致HCCI燃烧提前;充量温度低或发动机转速低时,混合气形成质量差,对HCCI燃烧有不良影响;指示热效率为30%-43%,其值高于火花点火发动机;预燃室的存在有利于稳定的HCCI燃烧;超稀充量运行可以显著降低NO排放。关键词;HCCI燃烧;异辛烷;乙醇;异辛烷—乙醇混合燃料Introductionresults in poor fuel economy and increased engine emis-The automotive industry has been forced to re- sions. The homogenous charge compression ignitepond to the increasing environmental concerns of con- HCCI) engine combines the use of premixed air fuelsumers and the rising cost of fossil fuels. Furthermore, mixture, usually associated with spark ignition SI)the prevailing mode of operation for premixed charge engines, with self-ignition induced by high compressionengines,such as gasoline engines, is mostly in partial ratio,中国煤化工 mpression ignitionload or with the throttle valve partially closed, which (CI)CNMHGuS consequences of2007-01-09;修回日期:2007-05-11。:加拿大21世纪汽车资助项目(D01DAF)。张春化,博士,教授, E-mail:zch@chd.ddh,m2007年9月张春化等:异辛烷、乙醇及其混合燃料HCCI燃烧的试验研究和分析(英文)such an organization of the engine combustion process, The fuel system is designed to be compatible for operationsuch as increased thermal efficiency, lower cycle tem- with alcoholsperatures and reduced NO, emissions. To ensure de-The HCCI engine has a modified cylinder head withsired ignition timing and to moderate reaction rates dur- a secondary piston and spacer arrangement that plungesing combustion, the air-fuel mixtures need to be lean or into the engine pre-chamber. By adjusting the plungeeven ultra-lean. While there are numerous advantagesspacer widthe compression ratio can be varied bein exploiting HCCI operation, there are also a number tween 15: 1 and 22: 1. A Kistler piezoelectric wall-mount-of issues need to be addressed. HCCI combustion lacks ed transducer is mounted in the glow plug hole to acquirea means of combustion on-set and subsequent pressure in-cylinder pressure. A combustion analysis systemrise control, since both the spark ignition timing( SI CAS)is used to acquire the pressure and crank angleengine)and the injection timing( CI engine)are ab- data. The CAS system has a resolution of 0. 1 CA forsent. HCCI operation is usually limited to part-load both pressure and encoder measurements at the maximumrated speed. The data acquisition system has a real-timeEthanol is used in this study since it is an alternativeto analyze engine parameguch asfuel produced domestically. It has been an attractive fuel maximum pressure rise rate, peak pressure, etc. The en-of choice in IC engines due to the potential reduction of gine-out emissions are measured by a portable Micro-GasCO, that occurs during the production of crops. Oakley et TM 5-gas analyzeal+ experimented with a variety of fuels, including etha2 Test Conditionsnol, to determine the in-cylinder conditions necessary toobtain HCCI combustion in a 4-stroke engine. They foundThe engine specifications and test conditions used inalcohols to be much more tolerant to air and exhaustthis study are shown in Tab. 1recycled(EGR)dilution. The study by Guerrieri et al[33showed that addition of ethanol decreased co and Hc e-Tab 1 Engine specifications and test conditiongmissions, while increased fuel consumption, NO, and acion ratIoetaldehyde emissionsIn this study, the engine performances are evalua-ted based on cycle-resolved in-cylinder pressures inEquivalence ratio()terms of heat release rate (HRR), indicated mean ef- Engine speed/(r/min)805,1035,1275,1520fective pressure( IMEP) and indicated thermal efficienCoolant temperature (T)/C75(±2)cy. Furthermore, regulated engine-out emissions are al-Intake charge temperature(T)℃120~150(±15)1 Experimental SetupThe fuels are 100% ethanol. 100% iso-octaneA four stroke, three-cylinder IDI Ci engine isand 50% iso-octane and 50% ethanol blend by vol-verted to a single cylinder HCCI operation. An electro- ume. The volumetric efficiency of the engine is bemagnetic injector is added in the intake pipe to form hotween 80% and 72%. The results reported in the nextmogenous charge in cylinder. The engine is motored by section are averaged data based on sampled 125 indi-an AC motor with a variable speed drive. An intake air vidual cycles.pre-heater and a temperature controller are used to keep 3 Results and Discussionstake air temperature constant. A laminar flow element中国煤化工in conjunction with a differential pressure transmitter is 3CNMHused to measure the air-flow rate. A number of K-typee in-cyninaer pressure and HRR o-thermocouples are installed along the intake and exhaust ver different intake charge temperatures and enginepipes to record the intake and exhaust gas temperatures.speeds. The intake charge temperature for ethanol is416内燃机学报第25卷第5期varied between120℃and140℃, and between130℃and150℃ for iso-octane and the blendL472℃Data in Fig. 1 indicate that for a particular fuel1373℃and engine speed, the intake charge temperature has aCylinder press126.7℃strong impact on the on-set of combustion. For exam14721373℃ple, in Fig 1a, the on-set of combustion advances267℃from1.3° CA BTDC to3.8° CA BTDC when the intake charge is increased from126.7℃to147.2℃0-15-10-50ence has been reported by several other reCrank Angle°cAsearchers earlier 4-. For a particular engine speedand intake charge temperature, it can be noted thato)100% iso-octane at 805 r/ miethanol advances the on-set of combustion compared toiso-octane. For example, the on-gets of combustion in1472℃the cases of ethanol and iso-octane at 1 035 r/min and136℃are5.6° CA and2.9° CA BTDC. This trend1373℃is confirmed with the blend where the on-set of combusCylinder presstion at1035r/ min and136℃is3.8° CA BTDC,1472℃1373℃126.7℃which is between the valueg of ethanol and iso-octaneHRRSimilar results have been reported in references [7]toreferences [10]5101520Crank Angle/CAThere is an interesting trend that separates lowerspeeds(803 r/min and 1 035 r/min) from higherb)100% iso-octane at 1 035 t/minspeeds(1 275 r/min and 1 520 r/min) when the intake charge temperatures are low. From the hrr, itcan be noted that ethanol and the blend show consistentignition without misfire at lower speeds (805 r/minand 1 035 r/min). Whereas, for the same fuels and4 cylinder pressure126.8℃er speeds(1275r/min a1358℃1459℃1 520 r/min)show either total or partial misfire. This1268℃behavior ig also observed for iso-octane with total mis.fire at higher speeds. While at lower speeds there is ei0-15ther partial or consistent ignition. This particular effectof either partial or total misfire at higher speeds forc)50% iso-octane and 50% ethanol blend a 805 r/minlower intake charge temperatures can be linked toctors: heat losses due to heat transfer and quality of1459℃It should also be noted that1358℃Fig. 1 a- Fig. 1f),1 035 r/min showed an overall1268℃4 cylinder pressu1358℃faster pressure rise rate and higher peak pressure com-1459℃一1268℃pared to 805 r/min. also, at higher speeds( Fig. 1 g更圣Fig. 11), 1 520 r/min shea better trend than中国煤化工1 275 r/min. This behavior was consistent during theCNMHexperimental trials and might be the particular characviaE nigOterstic of this engined)30% iso-octane and 30% ethanol blend at 1 035 r/min200年9张春化等异辛烷、乙醇及其混合燃料HCCI燃烧的试验研究和分析(英文)417131.7℃1358℃145.9℃1219℃-1358℃26.8℃HRRHRR0-15-10-5051015200-15-10-505101520Crank Angle/·cAe)100% ethanol at 805 r/mini)50%iso-octane and 50% ethanol blend at 1 275 /min1358CYlinderCylinder pressure1259℃l459℃1317℃￥121.9℃1268℃Crank Angle/°CACrank Angle·cAf100% ethanol at 1 035 t/mins0% iso-octane and 50% ethanol blend at 1 520 r/min136.0℃147.2℃137.31259℃Cylinder press1472℃136.0℃1259℃1373℃12Crank Angle/"CA1472℃1373℃1317℃259℃126.7。Cylinder press1472℃1360℃1259℃219℃中国煤化工-1-15-10-5CNMHGA 1O 5 20b)100% iso-octane at 1 520 v/min1)anol a 1 520 r/minFig 1 In-cylinder pressure and HRR418内燃机学报第25卷第5期3. 2 IMEP and COVduring 30 CA to 150 CA of the expansion stroke whereFig. 2 shows the IMEP and the COv Imer for the vari- the change of cylinder volume is large. For ethanol, thereous operating conditions. In Fig. 2, the IMEP curves are is not much difference in IMEP values at 805 r/min andthe solid dots and the COV MEP curves are the hollow 1 035 r/min, with 125.9C and 121.9 C giving adots. The IMEP is the net value which includes pumping slightly higher IMEP values compared to other initialloses. From Fig. 2, it can be noted that the CovIyEp charge temperatures. Whereas, at 1 275 I/ min, the besthas very high levels at the low initial charge temperatures IMEP value is at 131.7C, and at 1 520 r/min,where there is partial or complete misfire. In addition, IMEP value is at 125.9for iso-octane at different operating conditions, there is aspecific charge temperature that gives optimal combug-This trend can also be seen clearly fornol and the blend at higher speeds Fig 2c andFig. 2d)For iso-octane, 147.2c givee the best IMEP val-is evident from the HRR and pressure profile that this 0. s5ue at 1 035 r/min and 1 275 r/min. At 1 275 r/min, itcOVoperating point features better combustion characteristicsthan other temperatures. Whereas, at 1 035 r/min, almost the game imep values are attained at 147. 2C andIso-octane·◆·" Ethanol·““ Blend137 3C intake temperatures even though there is siga)An 805 r/minnificant difference in their pressure and HRR profilesFig 1b). At 147. 2C, only a little improvement for0.3IMEP is gained. The pressure curve of 137 3t at first◆stays below that of 147.2C till 15 CA ATDC. It0.2should be noted that the cylindehange is smallhen the piston is close to TDC and significant volumee2a2change occurs only during 30% CA to 150 CA. Hence,the above noted shift in the pressure curve plays a rolethe work done during the expansion stroke In additionOAthe peak pressure and temperature at 137 3C are low-Intake Charge Temperature/Cer than at 147. C. This in-effect reduces the heatBlendIso-octanetransfer losses at 137 3C, especially when the pistonBlendIso-octaneis close to TDC. This combined effect due to the shiftb)At 1 035 E/minthe pressure curve and difference in the heat transfer log-0.3ses results in similar IMEP valueg for both 147.2.C andIMEP137.3℃0HRR profile. Similar trend is found for iso-octane at 805r/min and 1 520 r/min where the IMEP value of0.l137.3℃ is better than that of147.2℃For the blend, 1358C initial charge temperaturegives the best IMEP value for all test speeds even though中国煤化工the pressure profile of 1459C is close to TDC. This is432158CNMHGe/℃again due to lower heat transfer rates resulting from lowerL. Blend - r 19o-octanepeak temperatures compared to 145.9 C case and the-· Ethanolthe pressure curve between these two temperaturesc) At 1 275 r/min2007年9月张春化等:异辛烷、乙醇及其混合燃料HCCl燃烧的试验研究和分析(英文)419·D IMEPAs mentioned earlier, the thermal efficiency increa-ses with engine speed. It should be noted that the volumetric efficiency for a given intake temperature condition0.ldrops by 6% when the engine speed is increased from805 r/min to 1 520 r/min. Hence the amount of intakeCoYcharge per cycle does not change significantly with in-crease of engine speed. From engine-out emissions in Fig 4··- Ethanol-· Blend-▲ lso-octar◆…=∴d)At 1 520 w/minFig 2 MEP and CoVerFor the highest IMEP valrremain less than 6% under all test conditions. Similarvalues for richer mixturea large amount of125130135140145trapped residual gas at 1 500 r/min in reference [9]Intake Charge Temperature/CIn this paper, the authors also reported a sharp in-o.- Ethanol O. Blend -A Iso-octanecrease in the Cov IMeP with lean mixture. In our experi-A)At 805 t/minments the mixture is very lean compared to that of refer-ence [11], and still the COVIE stays below 6%.Oneof the reasons for stable operation is due to presence ofthe pre-chamber in this iDi type engine, where there is2trapped residual gas that acts as an ignition source forsubsequent cycles once the initial cycle with combustion occurs3.3 Indicated thermal efficiencyig. 3 shows the indicated thermal efficiency(ni)125130135hich is calculated as the ratio of net indicated workIntake Charge Temperature/tproduct of fuel inducted per cycle and lower heating val-ue of fueL. In addition, this figure shows the peak pres·- EthanolBlend一 Iso-octanesure locations. In Fig 3, the n curves are the solid dotsb)At 1 035and the peak pressure location curves are the hollowdots. The trends in efficiency are similar to the IMEPsince the amount of input energy remains constant. Theindicated thermal efficiency is between 30% and 45%and increases with engine speed. The net indicated ther-mal efficiency reported in reference 12 ]for similarlean charges of ethanol and iso-octane is about 38% and40%(compression ratio used in that study is 18 and theequivalence ratio is 0. 35 for iso-octane and 0.33 for中国煤化工14515ethanol). TheefIciency values reported here are lowerCNMHthan that of reference 12]because of the iDi type en-鲁··B|endEthanolne used herec)At 275 v/min内燃机学报第25卷第5期were reported in reference[ 13] for iso-octaneIt can be seen that THC emissions are from 750 x10-6 to 1 150 10-6, and CO emissiong are from 0. 15%to 0.26%. In general, the CO and THC levels are highandre exhaust gas after-treatment. Again, theseLocationin CO and THC emissions might be due to theIDI type engine, which has greater heat losses that con-25130135140tribute to incomplete combustion especially close to theIntake Charge Temperature/Ccylinder walls. Similar levels of THC and Co for i9o-oC-◆·- Ethanol ..--Blend-Iso-octanetane are reported in reference [13]· Ethanol D. Blend4 Conclusionsd)At 1520 I/minFig 3 Indicated thermal efficiency and peak(1) For the same intake charge temperature andpressure locationengine speed, the on-set of combustion for ethanol occursahead of that for iso-octanethe combustion quality does not improve significantly w( 2) The HRR and in-cylinder pressure traces inincrease of thermal efficiency, which mainly results fromdicate that at lower charge temperatures and enginethe heat transfer losses. From the results obtained, it ap- speeds, the fuel-air mixtures'quality is not good, whichpears that the residence time of in-cylinder charge and theresults in poor on-set combustion.heat transfer losses decreases with increase of engine(3) The indicated thermal efficiency values arespeed and results in improved thermal efficiency30%-43%, better than those of typical SI engines.3. 4 Exhaust emissions(4) The presence of pre-chamber in this IDI typeFig 4 shows the carbon monoxide(co) and totalengine ensures stable operation COVIMEP stays belownon-methane unburned hydrocarbon THC )engine-ou%)due to trapping of residual gas thatemissions that correspond to the best IMEP valuestion source for subsequent cycles once the initial cycleeach engine speed and fuel. Hence, the intake chargewith combustion occurtemperature may not be the game for a given speed and(5) For the test conditions, NO, emissions arefuel. The oxides of nitrogen(NO, are not shown in thevery low(less than 10 x10), which might not requirfigure since the maximum value read is less than 10 xafter-treatment. However, the THC and Co levels are so10-6 for the entire test condition. This shows that nearhigh that would require after-treatmerzero No. emissions can be obtained by ultra-lean chargeSimilar results for No, for the equivalence ratio of 0. 321 References[1] Zhao Fuquan, Thomas W Asmus, Dennis N Assanis, et al.Editors,Homogenous Charge Compression Ignition( HCCI)Engines-Key Research and Development Issues[C]. SAEEFT94,1994.舍一—套0.3[2] David E Foster, Takeshi Morikawa, Tanet Aroonsrisopon,etal.An Investigation into the Eect of Fuel Composition on:HCCI Combustion Characteristics[C]. SAE Paper 2002-012830,2002.[3]Oakley A Zhan Ma t et al. Dilution Effects on the Con-中国煤化工 stion of Hydrocarbon andn/(r/min)Blend coC Gge Compression Ignition●·- Ethanol tho(HCCI)Engines-Key Research and Development Iss[C]. 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