喷油策略对直喷汽油机快速起动的影响

Effect of Injection Strategy on Quick Start of Gasoline Direct Injection Engine

摘要:

运用CFD(computational fluid dynamics)手段，对一款缸内直喷汽油机快速起动工况中的二次喷油策略进行分析研究.结果表明：过早的初次喷油会在活塞表面形成大量的油膜，导致燃油蒸发量过少，使得缸内混合气过稀，无法满足点火要求；第一次喷油越迟，滞留在排气门坑处的浓混合气越多，导致未燃碳氢排放增加，常温初次喷油时刻应设定在270° CA（曲轴转角）～240° CA BTDC（上止点前）范围内；相较于第一次喷油，在压缩过程中的第二次喷油对壁面油膜的影响较小，早于90° CA BTDC的喷油会导致液滴与缸套发生较多的碰撞；根据仿真结果，常温冷机起动的第二次喷油时刻应当设定在90° CA BTDC之后.

Abstract:

The research on two stage spray strategy of quick start of one gasoline direct injection（GDI）engine is studied by using the computational fluid dynamics (CFD) method. The result shows that，earlier first injection timing will cause much more oil film on the surface of piston and less fuel evaporation which may lead to dilute mixture in cylinder and the ignition requirements can’t be met. Then later first injection timing may result in more rich mixture being detained in the exhaust valve pit which will lead to more hydrocarbon emissions. The first spray timing should be set from 270° CA BTDC(before top dead center) to 240° CA BTDC. Compared to the first injection, the influence on oil film of second spray timing during compression process is little. The injection timing earlier 90° CA BTDC may cause more crash between droplets and cylinder liner. According to the simulation results, the second injection timing should be set after 90° CA BTDC.