汽油机分层燃烧引燃汽油压燃试验研究
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摘要
在一台中置压电晶体喷油器的缸内直喷单缸汽油机上,通过凸轮轴设计实现小气门升程和负气门重叠角。在发动机转速为2 000 r/min,IMEP为0.28 MPa工况,在高内部残余废气率下引入传统分层燃烧的控制方式,研究分层燃烧对汽油压燃的影响。研究结果表明:在高内部残余废气率下,可实现火焰传播的分层燃烧,大量内部废气的存在使燃烧滞燃期增长,NOx排放明显降低。而在典型的汽油压燃工况,调整两次喷射中二次晚喷的喷油量和喷油时刻,可控制缸内燃油分层程度,从而控制汽油压燃的燃烧相位。但随着内部残余废气率的降低,简单的燃油分层和引入火花点火无法实现稳定的压燃燃烧,此时采用分层燃烧的喷油和点火时刻组合,可以利用分层燃烧保证前期火焰传播的稳定性,实现缸内剩余燃油的自燃。这种分层引燃压燃的混合燃烧方式,点火时刻对于火焰传播及燃油的着火时刻有直接的控制作用,改变二次喷射比例对于燃烧相位的影响较小。当二次喷射比例增加到75%时,分层引燃对压燃的影响从单一的温度影响转变为温度和燃油浓度共同影响,导致燃烧稳定性变差。
The camshaft is designed to realize the low valve lift and negative valve overlap on a direct injection gasoline single cylinder engine with center-mounted piezo injector.The control method of stratified combustion is induced with higher internal residual exhaust gas fraction(RGF)when the speed of engine is 2000r/min and the IMEP is 0.28 MPa.The influences of the stratified combustion on compression ignition are studied and the result showed that the flame propagation can be realized under higher internal RGF.The ignition delay is longer and NOx emission is lower because of the massive residual exhaust gas.In the gasoline compression ignition condition,the combustion phase could be controlled by adjusting the mass and timing of late injection which could control the fuel stratified level.As internal RGF decreases,simple fuel stratified and spark ignition is useless to realize the compression ignition.But the fuel injection strategy and spark timing of stratified combustion could produce stable flame propagation and then realize the compression ignition of residual fuel.In the stratified combustion induced compression ignition method,ignition timing could directly control the combustion timing,as a result of that,second injection ratio had little influences on the combustion phase.When the second injection ratio increased to 75%,the stability of combustion is worse because the control element of compression ignition is changed from single temperature to dual elements,temperature and concentration.
The camshaft is designed to realize the low valve lift and negative valve overlap on a direct injection gasoline single cylinder engine with center-mounted piezo injector.The control method of stratified combustion is induced with higher internal residual exhaust gas fraction(RGF)when the speed of engine is 2000r/min and the IMEP is 0.28 MPa.The influences of the stratified combustion on compression ignition are studied and the result showed that the flame propagation can be realized under higher internal RGF.The ignition delay is longer and NOx emission is lower because of the massive residual exhaust gas.In the gasoline compression ignition condition,the combustion phase could be controlled by adjusting the mass and timing of late injection which could control the fuel stratified level.As internal RGF decreases,simple fuel stratified and spark ignition is useless to realize the compression ignition.But the fuel injection strategy and spark timing of stratified combustion could produce stable flame propagation and then realize the compression ignition of residual fuel.In the stratified combustion induced compression ignition method,ignition timing could directly control the combustion timing,as a result of that,second injection ratio had little influences on the combustion phase.When the second injection ratio increased to 75%,the stability of combustion is worse because the control element of compression ignition is changed from single temperature to dual elements,temperature and concentration.
引文
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15 Persson H,Sjholm J,Kristensson E,et al.Study of fuel stratification on spark assisted compression ignition(SACI)combustion with ethanol using high speed fuel PLIF[C].SAE Paper 2008-01-2401
2 Kontarakis G.,Collings N.,Ma T.Demonstration of HCCI using a single cylinder four-stroke SI engine with modified valve timing[C].SAE Paper 2000-01-2870
3 Tian Guohong,Wang Zhi,Wang Jianxin,et al.HCCI combustion control by injection strategy with negative valve overlap in a GDI engine[C].SAE Paper 2006-01-0415
4 Cao Li,Zhao Hua,Jiang Xi,et al.Numerical investigation into effect of fuel injection timing on CAI/HCCI combustion in a four-stroke GDI engine[J].International Journal of Computational Methods in Engineering Science and Mechanics,2006.7(1):41-57
5 Yap D,Wyszynski M L,Megaritis A,et al.Applying boosting to gasoline HCCIoperation with residual gas trapping[C].SAE Paper 2005-01-2121
6 Cairns A,Blaxill H.The effects of combined internal and external exhaust gas recirculation on gasoline controlled autoignition[C].SAE Paper 2005-01-0133
7 Chen T,Xie H,Li L,et al.Continuous load adjustment strategy of a gasoline HCCI-SI engine fully controlled by exhaust gas[C].SAE Paper 2011-01-1408
8 Natarajan V K,Sick V,Reuss D L,et al.Effect of sparkignition on combustion periods during spark-assisted compression ignition combust[J].Combustion Science and Technology,2009,181(9):1187-1206
9 Wang Z,Wang J,Shuai S,et al.Research on spark induced compression ignition(SICI)[C].SAE Paper 2009-01-0132
10 Yang C,Zhao H.In-cylinder studies of hybrid combustion in a direct injectionsingle-cylinder optical engine[J].International Journal of Engine Research,2010,11(6):515-531
11 Olesky L M,Martz J B,Lavoie G A,et al.The effects of spark timing,unburned gas temperature,and negative valve overlap on the rates of stoichiometric spark assisted compression ignition combustion[J].Applied Energy,2013,105:407-417
12 Benajes J,García A,Domenech V,et al.An investigation of partially premixed compression ignition combustion using gasoline and spark assistance[J].Applied Thermal Engineering,2013.52(2):468-477
13 Berntsson A W,Denbratt I.HCCI combustion using charge stratification for combustion control[C].SAE Paper 2007-01-0210
14 Xie H,Li L,Chen T,et al.Study on spark assisted compression ignition(SACI)combustion with positive valve overlap at medium-high load[J].Applied Energy,2013,101:622-633
15 Persson H,Sjholm J,Kristensson E,et al.Study of fuel stratification on spark assisted compression ignition(SACI)combustion with ethanol using high speed fuel PLIF[C].SAE Paper 2008-01-2401