冷起动两次喷油直喷汽油机的缸内可视化与排放

摘要

以可视化方法,试验研究了直喷(GDI)汽油机冷起动工况燃油两次喷射策略的污染物排放.采用光学单缸机和两台高速摄像机,同时从相互垂直的两个方向,记录燃油在气缸内的喷雾与燃烧过程,以燃烧分析仪分析燃烧稳定性,通过碳烟瞬态采集系统,分别用CLD500型和HFR500型火焰离子化检测仪(FID),对碳烟、NOx和HC进行记录分析.结果表明:在冷起动工况,第2次喷油正时过晚,燃油撞击活塞顶形成油膜,雾化不充分,会导致碳烟排放过高;第2次喷油正时提前,燃烧稳定性提高;增加第一次喷射的燃油质量比,可改善碳烟、NOx和HC排放,但略降低燃烧稳定性.%Pollutant emissions for a Gasoline Direct lnjection (GDl) engine with double injection at cold start incylinder process were investigated using a visualization method. The spray and combustion images in an optical single cylinder engine were recorded simultaneously from two directions perpendicular to each other utilizing two high-speed cameras. A combustion analyzer and a micro-soot-sensor were used to analyse combustion stability and soot emission. A CLD500 type fast NOx system and a HFR500 type fast Flame lonization Detector (FlD) system were used to sample nitrogen oxide and hydrocarbon emission. The results show that the main reason for high soot emission caused by impinging more fraction fuel on piston crown and forming oil film under cold start condition using delayed second injection timing. While, advancing second fuel injection improves combustion stability. lncreasing first injection fraction decreases the emissions of soot, NOx and HC with a slight negative effect on the combustion stability.