米勒循环与EGR对汽油发动机影响的试验研究

基于一台带有低压废气再循环系统(Exhaust Gas Recirculation, EGR)的1.5 L涡轮增压直喷汽油发动机,通过改变进气凸轮型线,试验研究了米勒循环与废气再循环对部分负荷和最优油耗点的燃烧、燃油经济性等方面的影响。结果表明:在部分负荷下,米勒发动机节气门开度大,进气压力高,泵气损失小,但随着负荷的增加,米勒效应减小,降低泵气损失的能力下降,对燃油经济性的改善减小。米勒循环可以降低压缩终了温度,使得燃烧重心提前,但是米勒循环燃烧持续期延长,排气温度高,米勒循环对最优油耗点的改善能力较小。随着EGR率的增加,有效燃油消耗率先减小后上升,米勒循环减少了进气时间、降低了进气门升程,缸内滚流比和湍动能大幅下降,燃烧重心推后,燃烧持续期延长,EGR对米勒循环发动机的燃油经济性的改善能力低于奥托循环。

Experimental Study on Effect of Miller Cycle and EGR on Performance of a Gasoline Engine

Based on a 1.5 L turbocharged direct injection gasoline engine with a low-pressure exhaust gas recirculation system(LPEGR),the effects of Miller cycle and exhaust gas recirculation on combustion and fuel consumption at part load and optimal fuel consumption point were studied by changing the intake camshaft profile.The results show that under part load,the throttle opening of Miller engine is large,the intake pressure is high and the pump loss is small.But with the increase of load,the Miller effect decreases,the ability to reduce pump loss decreases,and the improvement of fuel economy decreases.Miller cycle can reduce temperature at compression TDC and advance the combustion center,but Miller cycle can prolong the combustion duration and increase the exhaust temperature.Miller cycle has less ability to improve the optimal fuel consumption point.With the increase of EGR rate,the effective fuel consumption rate decreases first and then increases.Because Miller cycle reduces the intake time and valve lift,the tumble ratio and turbulent kinetic energy in cylinder decrease greatly,the combustion center is delayed,and the combustion duration prolongs.The improvement ability of EGR on the fuel economy of Miller cycle engine is lower than that of Otto cycle.