滚流比对缸内直喷汽油机燃烧速度的影响研究

Study on Effect of Tumble Ratio on the Combustion Speed of GDI Engine

滚流比会影响缸内直喷汽油机的混合过程,从而影响缸内燃烧。利用2种具有不同滚流比的单缸机缸盖,在汽油光学单缸机平台上开展了不同转速和负荷的试验研究,探究滚流比对滞燃期、碳烟排放与燃烧循环稳定性的影响。试验结果表明,提高滚流比能够减小喷雾宽度和喷雾锥角,提高火焰扩散速度。提高滚流强度能显著缩短发动机的滞燃期,推迟喷油正时,能够加强高滚流对滞燃期的缩短程度。对于不同的滚流比,从点火到火焰向单侧传播20 mm的时间与燃烧滞燃期息息相关。喷油正时较早时,低滚流比会引起燃烧循环波动增加、碳烟排放增加;但高滚流比不会引起燃烧循环波动和碳烟排放的严重恶化。因此,提高滚流强度能拓展最佳喷油正时。

The tumble ratio affects the mixing process of the direct injection gasoline engine and thus the combustion in the cylinder.In order to investigate the effects of tumble ratio on the ignition delay,soot emission and combustion cycle stability,two cylinder heads with different tumble ratio were used to carry out the experimental study of different speed and load on the gasoline optical single cylinder engine platform.The experimental results show that increasing the tumble ratio can reduce the spray width and spray cone angle and increase the flame diffusion rate.Increasing the tumble strength can shorten the ignition delay period of the engine.Delaying the injection timing can enhance the effect of tumble on the reduction of ignition delay.For different tumble ratio,the time interval between ignition and flame propagating to one side for 20 mm is closely related to combustion delay.When the injection timing is earlier,lower tumble ratio will increase the combustion cycle fluctuation and soot emission;however,higher tumble ratio will not cause this phenomenon.Therefore,the best injection timing can be extended by increasing the tumble ratio.