进气前回流对HCCI汽油机着火时刻的影响

摘要

In order to control HCCI auto-ignition timing,three-dimensional numerical simulation was performed to investigate the influence of the intake backflow caused by different intake valve opening timings on combustion.The results show that intake backflow ratio increases as intake valve opening timing advances,which plays two roles.One is that the in-cylinder average temperature changes due to heat losses,the other is that the in-cylinder temperature and residual gas fraction (RGF) distribution is changed by changing the mixing process of fresh and exhaust gas.When the intake backflow ratio is lower than 20％,the decrease of in-cylinder average temperature delays the ignition timing.When the intake backflow ratio exceeds 20％,the inhomogeneity increases of temperature and RGF,which makes the ignition timing advance.The intake backflow also decreases the overlapped area of high temperature zone and high RGF zone,resulting in a high temperature and relatively low RGF zone,which is beneficial to autoignition.The formation and development of this zone promotes the generation of auto-ignition sites,advancing the auto-ignition timing.%为了实现对着火时刻的调控,在负气门重叠角(NVO)策略下,通过进气门早开,形成不同程度的进气前回流,来调控着火时刻.三维仿真结果表明,进气门开启提前,前回流比例逐渐增大,产生两个主要的作用,一个是散热造成缸内平均温度发生改变,另一个是改变新鲜进气和废气的混合历程,使得缸内温度、废气分布发生变化.当前回流质量分数小于20％时,缸内平均温度的降低使着火时刻推迟.当前回流质量分数大于20％时,温度、废气不均匀度的增加使得着火时刻提前;前回流的存在还使得缸内高温区和高废气区的重合度减小,使缸内形成了利于着火的高温及相对低废气区,促进自燃点的出现,使着火时刻提前.