国六自动挡乘用车GDI发动机高瞬态HC原排分析

Analysis on High Transient HC Raw Emission of GDI Engine for ChinaⅥAutomatic Passenger Car

针对GDI发动机在部分瞬态工况下HC排放较高的问题,对一辆装有GDI发动机的轻型车在底盘测功机上进行WLTC试验,通过采集单缸瞬态HC排放、缸内燃烧压力和ECU控制参数数据,研究了部分瞬态HC排放高的原因。试验结果表明:发动机冷却液升温过程对发动机的HC排放没有显著影响,在WLTC试验的各个驾驶速度段均出现了高HC排放;当发动机扭矩从高到低急剧变化时,可能出现缸内未断油但进气量急剧减少的情况,导致发生缸内失火或不完全燃烧,从而产生高HC排放;另外,当气缸内连续几个工作循环断油后再喷油时,会导致缸内过量空气系数偏离最佳范围,使缸内燃烧状况恶化,甚至发生失火或不完全燃烧,从而引起HC排放增加。

For the phenomenon of high HC raw emission of GDI engine under partial transient conditions,a WLTC(world harmonized light vehicles test cycle)test was carried out on a light vehicle equipped with a GDI engine by using the chassis dynamometer.The transient HC emission,in-cylinder pressure and ECU control parameters of single cylinder were collected,and the reasons of high HC emission were studied.The results show that the warm-up of engine coolant has no significant effect on the raw HC emission,and the high HC emission segments appear in each driving speed segment of WLTC.When the engine torque changes sharply from high to low,the intake air sharply reduced,but the fuel may be not cut off in the cylinder,and in-cylinder misfire or incomplete combustion occur and results in high HC emission.In addition,when the fuel injects again after the cutoff of several continuous working cycles,the in-cylinder excess air coefficient may deviate from the optimal range,the in-cylinder combustion worsens,and then misfire or incomplete combustion occurs,and hence HC emission increases.