二次喷射对火花辅助压燃燃烧及爆震特性影响的试验研究
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摘要
火花辅助压燃(SACI)是一种由火焰传播诱导未燃混合气自燃的新型燃烧方式.但SACI爆震现象限制了热效率的进一步提升.针对这一问题,基于一台高压缩比缸内直喷汽油机,首先对SACI燃烧及爆震界定进行了分析;然后开展了二次喷射策略对SACI燃烧及爆震特性影响的试验研究.结果表明:火花点火是SACI燃烧的一个重要环节,点火过于提前会导致SACI爆震的产生.SACI爆震的压力振荡幅值(MAPO)要高于SI爆震且分布更加离散.二次喷射在燃烧室内可以形成不同的燃油浓度分层,对SACI有良好的爆震抑制效果.当采用喷射比例4∶1、一次喷射时刻300°,CABTDC、二次喷射时刻140°,CABTDC时,通过对爆震的抑制获得最优燃烧特性,循环变动系数降低了1.18%,,有效燃油消耗率降低了约3.11%,有效热效率提高了1.05%.
Spark assisted compression ignition(SACI)is a new combustion mode by inducing the auto-ignition of unburned mixture with flame propagation. However,the knock of SACI limits the increase of thermal efficiency. In this work,the combustion characteristics and knock detection of SACI were analyzed based on a gasoline direct injection(GDI)engine with high compression ratio. Besides,experiments were conducted to investigate the effects of split injection strategy on the combustion and knocking characteristics. The results show that the ignition timing is an essential factor influencing the knock occurrence. Engine knock is easily induced under SACI with excessive ignition advance. When the knock occurs,the maximum amplitude of pressure oscillation(MAPO)under SACI mode is more discrete and higher than that under the SI mode. Split injection can cause different levels of fuel concentration stratification in combustion chamber,which can suppress the engine knock efficiently. The optimal combustion characteristic is obtained through the improved knock resistance at an injection ratio of 4∶1,with an first start of injection(SOI)of 300°,CA BTDC and second SOI of 140°,CA BTDC. In this case,the coefficient of variation and the brake specified fuel consumption decrease by 1.18%, and 3.11%, respectively,the effective thermal efficiency increases by 1.05%,.
Spark assisted compression ignition(SACI)is a new combustion mode by inducing the auto-ignition of unburned mixture with flame propagation. However,the knock of SACI limits the increase of thermal efficiency. In this work,the combustion characteristics and knock detection of SACI were analyzed based on a gasoline direct injection(GDI)engine with high compression ratio. Besides,experiments were conducted to investigate the effects of split injection strategy on the combustion and knocking characteristics. The results show that the ignition timing is an essential factor influencing the knock occurrence. Engine knock is easily induced under SACI with excessive ignition advance. When the knock occurs,the maximum amplitude of pressure oscillation(MAPO)under SACI mode is more discrete and higher than that under the SI mode. Split injection can cause different levels of fuel concentration stratification in combustion chamber,which can suppress the engine knock efficiently. The optimal combustion characteristic is obtained through the improved knock resistance at an injection ratio of 4∶1,with an first start of injection(SOI)of 300°,CA BTDC and second SOI of 140°,CA BTDC. In this case,the coefficient of variation and the brake specified fuel consumption decrease by 1.18%, and 3.11%, respectively,the effective thermal efficiency increases by 1.05%,.
引文
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[2]Wang Z,He X,Wang J-X,Shuai S,et al.Combustion visualization and experimental study on spark induced compression ignition(SICI)in gasoline HCCI engines[J].Energy Conversion and Management,2010,51(5):908-917.
[3]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.
[4]Wang X,Xie H,Li L,et al.Wall temperature effect on SI-CAI hybrid combustion progress in a gasoline engine[C]//SAE Technical Papers.Detroit,USA,2013,2(1):1315-1323.
[5]Koopmans L,Denbratt I.A four stroke camless engine,operated in homogeneous charge compression ignition mode with commercial gasoline[C]//SAETechnical Papers.Detroit,USA,2001:2001-01-3610.
[6]Begg S M,Mason D J,Heikal M R.Spark ignition and spark-assisted controlled auto-ignition in an optical gasoline engine[C]//SAE Technical Papers.Detroit,USA,2009:2009-32-0072.
[7]Wang Z,Wang J,Shuai S,et al.Research on spark induced compression ignition(SICI)[C]//SAE Technical Papers.Detroit,USA,2009:2009-01-0132.
[8]Lavoie G A,Martz J,Wooldridge M,et al.A multimode combustion diagram for spark assisted compression ignition[J].Combustion and Flame,2010,157(6):1106-1110.
[9]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(1):622-633.
[10]Marseglia G,Costa M,Catapano F,et al.Study about the link between injection strategy and knock onset in an optically accessible multi-cylinder GDI engine[J].Energy Conversion and Management,2017,134:1-19.
[11]Benajes J,Molina S,García A,et al.Performance and engine-out emissions evaluation of the double injection strategy applied to the gasoline partially premixed compression ignition spark assisted combustion concept[J].Applied Energy,2014,134(C):90-101.
[12]Galloni E.Dynamic knock detection and quantification in a spark ignition engine by means of a pressure based method[J].Energy Conversion and Management,2012,64(12):256-562.
[13]Brecq G,Bellettre J,Tazerout M.A new indicator for knock detection in gas SI engines[J].International Journal of Thermal Sciences,2003,42(5):523-532.
[14]Wang Z,Liu H,Reitz R D.Knocking combustion in spark-ignition engines[J].Progress in Energy and Combustion Science,2017,61:78-112.
[15]Wagner R M,Edwards K D,Daw C S,et al.On the nature of cylic dispersion in spark assisted HCCIcombustion[C]//SAE Technical Papers.Detroit,USA,2006:2006-01-0418.
[16]Wei H,Feng D,Pan M,et al.Effects of multiple parameters on cyclic variation of a SI engine fueled with2-methylfuran gasoline blends[C]//SAE Technical Papers.Detroit,USA,2017:2017-01-0654.