Effect of equivalence ratio on diesel direct injection spark ignition combustion

当量比对柴油直喷点燃燃烧的影响

Aviation heavy-fuel spark ignition(SI)piston engines have been paid more and more attention in the area of small aviation.Aviation heavy-fuel refers to aviation kerosene or light diesel fuel,which is safer to use and store compared to gasoline fuel.And diesel fuel is more suitable for small aviation application on land.In this study,numerical simulation was performed to evaluate the possibility of switching from gasoline direct injection spark ignition(DISI)to diesel DISI combustion.Diesel was injected into the cylinder by original DI system and ignited by spark.In the simulation,computational models were calibrated by test data from a DI engine.Based on the calibrated models,furthermore,the behavior of diesel DISI combustion was investigated.The results indicate that diesel DISI combustion is slower compared to gasoline,and the knock tendency of diesel in SI combustion is higher.For a diesel/air mixture with an equivalence ratio of 0.6 to 1.4,higher combustion pressure and faster burning rate occur when the equivalence ratios are 1.2 and 1.0,but the latter has a higher possibility of knock.In summary,the SI combustion of diesel fuel with a rich mixture can achieve better combustion performance in the engine.

在小型航空领域航空重油点燃式活塞发动机受到越来越多的关注。航空重油指的是航空煤油或者轻质柴油,相比汽油燃料在使用和储存上都更安全。而柴油燃料更适合应用在陆地上的小型航空发动机中。本文采用数值模拟研究去评估汽油直喷点燃转换到柴油直喷点燃的可能性。其中柴油采用原有的汽油直喷系统直接喷入气缸并通过火花点燃。在模拟中,计算模型通过一台汽油直喷发动机的实验数据进行标定,并验证了模型的有效性。进而,在验证模型的基础上,研究了柴油直喷点燃燃烧特性。研究结果表明,柴油直喷点燃燃烧过程比汽油慢,并且柴油在点燃燃烧中的爆震倾向更高。对当量比从0.6到1.4的柴油/空气混合气,当量比为1.2和1.0时的燃烧压力更高,燃烧速率更快,但当量比为1.0的爆震可能性更高。综合来看,柴油燃料在发动机中的点燃燃烧采用浓混合气能获得更好的燃烧性能。