二次喷油优化直喷汽油机冷启动排放特性的研究

研究了一种通过特殊活塞顶面形状结合二次喷射策略来解决直喷汽油机冷启动工况排放问题的新方法.该方法通过适当的二次喷油分配、结合缸内气流运动来改善燃油混合气的分布.利用AVL-Fire对不同喷油策略下直喷汽油机启动时缸内油气混合分布进行了模拟,对不同喷油策略的冷启动排放进行了实验研究.结果表明,采用特殊活塞顶面形状进行合理的壁面引导,同时结合二次喷油策略,能够优化直喷汽油机冷启动工况下缸内空燃比的分布,使得混合气浓度在火花塞附近略高,宜于火花点火,在火花塞周围略低,宜于火焰传播,从而提高燃烧的稳定性,减少燃油的湿壁现象,降低HC的排放.

Study of Two-Stage Injection in Optimizing Cold-Start Emission Characteristics of GDI Engine

A new solution to the cold start emissions of gasoline direct injection(GDI) engines was presented with two-stage injection strategy and special design of piston crown to improve the distribution of the air-fuel mixture and the combustion stability.AVL-Fire was used to simulate the distribution of fuel-air mixture in a cylinder under cold start condition.The cold-start-exhaust experiment with different injection strategies was conducted.The results show that the two-stage injection strategy combined with reasonably guiding the air flow would optimize the distribution of the fuel-air ratio in the cylinder under cold start condition,thus improving the characteristics of the spark ignition and the spread speed of the flame front,and mitigating fuel wetted-wall phenomenon.It seems that the present method may enhance the combustion stability and reduce the HC emissions.