对置活塞二冲程汽油机分层稀燃组织研究

结合对置活塞二冲程汽油机缸径小、冲程长的特点，提出了进排气侧非对称喷雾方式，并采用AVL-Fire软件对喷雾方向进行优化，实现全负荷工况下的缸内均匀混合；同时研究了部分负荷工况下二次喷射对分层混合气形成和稀燃组织的影响.结果表明，进气侧喷射角增大有利于提高缸内混合气的均匀度，排气侧喷射角增大会导致燃油蒸发率降低；二次喷油比例影响分层混合气浓稀区的分布，二次喷油时刻影响缸内混合气稀区的均匀性.当进气侧喷射角为30°、排气侧喷射角为15°时，选择第一次喷油时刻为220℃ A，第二次喷油时刻为270℃ A且二次喷油比例为20%，可有效组织混合气分层.在部分负荷工况下，采用分层稀混合气相比均匀稀混合气的火焰发展期缩短约30%，快速燃烧期缩短约15%. 

Research on Stratified Mixture Lean Burn of Opposed-Piston Two-Stroke Gasoline Engine

For the characteristics of small bore and long stroke for opposed-piston two-stroke gasoline engine,an asymmetric spray mode on exhaust and intake side was proposed in this paper and the spray direction was optimized with CFD AVL-Fire software to form the homogenous mixture in full load.The effect of two-stage injection strategy with different injection timing and injection ratio on mixture stratification and lean burn organization were simulated based on optimized spray direction.The results show that the increase of injection angle in intake side can improve uniformity index of mixture and the increase of injection angle in exhaust side can reduce fuel evaporation.The second injection ratio affects stratified mixture distribution and the second injection timing affects stratified mixture uniformity.When the injection angle in intake side is 30° and the injection angle in exhaust side is 15°,first injection timing at 220 ℃ A and the second injection timing at 270 ℃A with 20％ total fuel quantity finally lead to ideal in-cylinder mixture stratified distribution.In part load,stratified mixture distribution can shorten 30 ％ time of flame developing period and shorten 15％ time of rapid burning period compared with homogeneous mixture.