基于缸内净压力的直喷发动机最佳点火正时

摘要

为探求汽油机在不同工况下最佳点火正时与各燃烧特征参数的对应关系,在一台低压空气辅助单缸直喷试验机上进行变工况实验,利用自主研发的燃烧分析,系统对各工况的燃烧状况进行分析,对比了不同工况下50%燃烧量对应的曲轴转角(CA50)、最高燃烧压力对应的曲轴转角(PCP)、净压力二次导数峰值对应曲轴转角(MANP)3种燃烧特征参数与最佳点火正时之间的对应关系,并着重分析了净压力二次导数曲线的变化规律.研究表明,MANP作为一种新的燃烧特征参数能够较好地表征缸内燃烧的状况,并且与最佳点火提前角有很好的对应关系;CA50和PCP皆能在一定范围内与最佳点火正时有良好的对应关系,但仍有不确定性,相对而言,以MANP作为最佳点火正时的评价标准具有更高的精度.%To explore the relationship between MBT and combustion characteristic parameter under different con-ditions,an experiment in variable conditions was conducted in a single-cylinder GDI engine with a low pressure air auxiliary system.The corresponding relationship betweenthe spark timing for maximum brake torque(MBT) and CA50,position of peak cylinder pressure (PCP) andmaximum acceleration of net pressure(MANP) was analyzed using a self-development combustion analysis system,and then the variation law of the secondary guide curve of net pressure was studied.The result shows that as a new combustion characteristic parameter,MANP is good at characterizing combustion,and it has a strong corresponding relationship with MBT.CA50 and PCP can also in-dicate the MBT within a certain range,but with some uncertainty. Relatively speaking,compared with the other two,MANP shows greater accuracy as an evaluation standard for MBT.