稀燃和EGR对汽油发动机热效率影响的试验研究

Experimental study on the effect of lean burn and EGR on thermal efficiency of gasoline engine

在一台4缸2.0 L汽油发动机上试验研究过量空气系数、有效压缩比、废气再循环(exhaust gas recircu-lation, EGR)率对发动机油耗和热效率的影响。结果表明:采用稀燃可以提高发动机热效率,过量空气系数由1.0增大到1.6,发动机热效率提高约5.7%,但继续增大稀释程度将导致油耗增加、热效率降低;当有效压缩比为12.7时,发动机热效率最大,为44.1%,进一步增大压缩比产生爆震,需要推迟点火时刻,导致燃烧持续期增加、发动机热效率降低;EGR率为4.6%时,发动机热效率最大,为44.4%,EGR率较大导致燃烧不稳定,出现发动机失火等问题。

An experimental study is conducted on a 4-cylinder 2.0 L gasoline engine to investigate the effects of excess air coefficient,effective compression ratio,and exhaust gas recirculation(EGR)rate on engine fuel consumption and thermal efficiency.The results show that the use of lean burn technology can improve the thermal efficiency of the engine,the engine thermal efficiency increases by approximately 5.7%when the excess air coefficient increases from 1.0 to 1.6,however,further dilution would increase fuel consumption and reduce thermal efficiency.The engine has the highest thermal efficiency of 44.1%when effective compression ratio is 12.7,but further increase in compression ratio will cause engine knocking,which requires delaying the ignition time,which can lead to an increase in combustion duration and a decrease in engine thermal efficiency.In addition,the EGR rate(4.6%)could achieve the highest thermal efficiency,44.4%,but unstable combustion and misfire will occur in the engine when EGR rate increased further.