理论空燃比下废气再循环率对汽油机性能的影响

为了提高某增压汽油机的性能,将其压缩比提高到11.5,并加装一套EGR循环系统。通过台架试验,在低速小负荷和中速中负荷工况下,研究了理论空燃比下废气再循环率对改造后汽油机性能的影响。结果表明:当EGR率小于20%时,采用合适的EGR率配合优化的点火时刻,可以使该发动机燃烧稳定,在保证发动机动力性的同时,指示热效率随着EGR率的增加不断升高;与无EGR时相比,EGR率为20%时,有效燃油消耗率在低速小负荷工况下降低了约4.5%,中速中负荷工况下降低了9.7%;随着EGR率的增加,THC排放增加,而NOx排放显著降低,CO排放在低速小负荷时出现上下波动的现象,而在中速中负荷工况时,随着EGR率的增加不断降低。

Effect of EGR Rate on Gasoline Engine Performance under Theoretical Air-Fuel Ratio

In order to improve the performance of a supercharged gasoline engine ,the compression ratio was increased to 11 .5 and a set of EGR system was configured .Under the conditions of low load at low speed and medium load at medium speed ,the effects of EGR rate on the performance of retrofitted gasoline engine were studied based on the theoretical air‐fuel ratio through the experiments .The results show that the controllable EGR rate and optimized ignition timing can keep stable during combus‐tion process when the EGR rate is less than 20% .Meanwhile ,the indicated thermal efficiency increases with the increase of EGR rate .Compared with non‐EGR ,the brake specific fuel consumption decreases by 4 .5% at low speed and load area and by 9 .7% at medium speed and load area when EGR rate is 20% .With the increase of EGR rate ,THC emission increases ,NOx emission decreases significantly and CO emission fluctuates at low speed and load and reduces at medium speed and load .