汽油HCCI发动机燃油预燃烧(FPC)过程的热功转换研究

Energy Conversion of In-Cylinder Fuel Pre-Combustion Process in Gasoline HCCI Engines

实现汽油机均质混合气压燃(HCCI)的难点是控制着火时刻和扩展负荷范围。在缸内直喷汽油机上利用负阀重叠(NVO)期间缸内预燃烧可以实现HCCI着火时刻控制和低负荷范围拓展。通过对预喷时刻、预喷油量以及NVO阶段氧的体积分数系统研究,分析了缸内燃油预燃烧热功转换过程及其对主燃烧过程的影响规律。结果表明:NVO阶段喷射的燃油在高温废气中发生的预燃烧是一种特殊的热功转换过程;燃烧放出的热量一部分转换成有效功,一部分加热缸内残余废气,提高了换气过程中平均压力,减少了泵气损失;预燃烧阶段放出的最大热量与NVO阶段废气中氧的体积分数有关,而相同氧的体积分数条件下放热量由此阶段燃油喷射时刻以及喷射量决定;预燃烧阶段的放热量直接影响主燃烧过程的燃烧相位从而影响循环指示效率。

The difficuties to realize gasoline HCCI combustion are ignition time control and load extension. Pre-injection during negtive overlap period in gasoline direct injection engines can be used to realize ignition time control and low load extension. Energy conversion during fuel pre-combustion process and its effects on the main combustion were analysed by studying the pre-injection timing, the pre-injection amount and the oxygen concentration. The results show that the fuel injected into the high-temperature exhaust gas during the NVO period is paktially burned and forms a special energy conversion process. Part of the released heat converts to effective work, part of the heat raises the temperature and pressure and reduces the pumping loss. The maximum value of heat released during fuel pre-combustion depends on the oxygen concentration and is influenced by the fuel injection timing and amount. The main eombusiton timing is directly influenced by the amount of released heat during fuel pre-combustion.