对置活塞二冲程汽油机燃烧特性试验

Experimental Study of Combustion Characteristics on an Opposed-PistonTwo-Stroke Gasoline Engine

通过对置活塞二冲程缸内直喷汽油机进行原理样机燃烧特性试验,研究了对置活塞运动相位差、扫气压力、点火正时和点火方式等对燃烧过程和整机性能的影响规律.对置活塞二冲程汽油机缸内放热规律试验结果与传统汽油机一致,可分为火焰发展期、快速燃烧期和燃烧后期.对置活塞运动相位差过小会导致缸内扫气效率较低、残余废气量较高,不利于燃烧过程的组织;同时,对置活塞相对运动速度过快会导致内止点过后气缸工作容积变化率较大,缸内压力和温度下降较快.对置活塞运动相位差为15°,CA时,可有效改善扫气过程和燃烧组织.随着转速的升高,需要提高扫气压力,在提高扫气效率的同时增加混合气质量,提高燃烧速率.扫气压力为0.12,MPa时可兼顾中、高转速下缸内扫气过程和燃烧组织.对置活塞采用平顶结构时,需要配合双火花塞对置点火且点火提前角为20°,CA,可保证中、高负荷具有最高的指示热效率.

Combustion characteristics of an opposed-piston two-stroke(OP2S)gasoline direct injection(GDI)engine was investigated through experiment.Effects of opposed-piston motion phase difference,scavenging pressure,ignition timing and ignition scheme on the combustion process and engine performances were discussed.Results show that the heat release rate of the OP2S-GDI engine is in accordance with the conventional gasoline engine,which is also divided into the flame developing period,the rapid burning period and the post burning period.With the increase of piston motion phase difference,the scavenging efficiency decreases and more residual gas is trapped in the cylinder,not beneficial to the combustion process.Meanwhile,the faster relative velocity of the two opposed pistons near the inner dead center enhances the change rate of the swept volume,leading to the rapid decline of the cylinder pressure and temperature.The 15°,CA of opposed-piston motion phase difference improves the scavenging and combustion process effectively.When the engine speed increases,higher scavenging pressure is required in order to improve the scavenging efficiency.As a consequence,the air/fuel mixing process and the combustion process are accelerated.When scavenging pressure is 0.12,MPa,both the scavenging efficiency and the combustion process are improved at medium-high speeds.It is noted that a flat piston structure of the OP2S-GDI engine needs dual spark plugs with an ignition advance angle of 20°,CA.Thus,the maximum of indicated thermal efficiency is achieved at mediumhigh load conditions.