航空直喷发动机缸内混合气形成的试验

基于航空活塞式基础样机的结构特点,自主研制了单缸低压直喷全透明光学发动机,并利用高速摄影对缸内混合气形成进行试验研究.分析了不同燃烧室形状、燃油启喷时刻以及发动机转速等条件下低压直喷发动机缸内的混合气形成规律.研究结果表明:新设计的偏心碗型活塞顶面能够有效地引导燃油喷雾形成向燃烧室顶部卷吸的运动,从而使得燃油液滴聚集在双侧火花塞附近;燃油喷射时刻对混合气形成影响很大,当进气门开度较小且活塞与上止点距离较为适中时喷射燃油,混合气形成质量最好;进气运动较强烈时,发动机转速提高会加速燃油液滴的蒸发,但同时活塞顶面对喷雾的引导作用被削弱,混合气形成质量变差;当进气运动变弱时,发动机转速提高会增强活塞顶面对油束的作用,即引导作用变强.

Experiment of in-cylinder mixture formation process low-pressure GDI engine

A low pressure direct injection transparent optical engine bench was developed,and the in-cylinder mixture formation process was filmed.Different mixture formation patterns were analyzed in conditions of different combustion chamber geometries,fuel injection timings and engine speeds.The research results show that:guidance of the combustion chamber with decentralized cavity piston is better than that of the proto-engine's combustion chamber;fuel injection timing plays a key role in the mixture formation,and a good mixture formation can be obtained if choosing an injection timing when intake flow is not that strong and the piston moves in the middle position of the cylinder,when the intake flow is strong,an increased engine speed can accelerate the evaporation of the fuel droplets,but the guidance of the combustion chamber is weaked,which results in a bad mixture formation.On the contrary,when the intake flow is weak,higher engine speed can promote the effect of combustion chamber's guidance to the fuel plume.