基于折射率匹配法GDI发动机附壁油膜特性

Study on GDI Engine Spray Wall Film Based on Refractive Index Matching Method

在当前发动机轻量化和高喷射压力的趋势下,采用多孔喷油器的缸内直喷汽油机容易发生喷雾坍塌和燃油碰壁,并在活塞表面形成附壁油膜.为了研究燃油温度对碰壁特性的影响,采用折射率匹配法,系统考察不同燃油温度下的喷雾碰壁的宏观形态,分析油膜厚度分布和蒸发过程.研究表明:低燃油温度未发生闪沸条件下,各雾束对应的油膜独立、厚度较大且蒸发速度慢;随着燃油温度升高当达到闪沸条件时,开始发生喷雾坍塌现象,最大油膜厚度减小且燃油分布均匀,蒸发速度加快;随着温度继续升高,在高燃油温度下燃油剧烈坍塌,壁面形成一片圆形的高厚度油膜,蒸发速度变慢.

Under the trend of engine lightweight and high injection pressure,gasoline direct injection(GDI)engines with multi-hole injectors are prone to spray collapse and impingement,resulting in fuel film on the piston.In order to study the impingement characteristics under different fuel temperatures,a refractive index matching method was used to investigate the macroscopic morphology of spray impingement and analyze the fuel film thickness distribution and the evaporation process.The results show that,at low fuel temperature without flash boiling,the fuel wall films impinged from each spray plume are separated each other and the film thickness is large with a slow evaporation rate.When the fuel temperature increases to reach the flashing point,the spray collapse begins to occur and the film thickness becomes thin and uniform with a fast evaporation speed.When the fuel temperature continues to rise,violent spray collapse can be seen under high fuel temperature,and the impingement footprint turns into an approximately spherical shape with a slow evaporation rate.