二次喷射对直喷增压汽油机混合气形成与燃油湿壁影响的数值研究

Numerical Research into Effect of Two-Stage Injection on Mixture Formation and Wall Wetting in a Turbocharged GDI Engine

使用数值仿真的方法对缸内喷雾、混合气形成和燃油湿壁进行了研究,重点对二次喷射对燃油湿壁的影响进行了详细的分区分析。对比分析了单次喷射方案和二次喷射方案仿真结果,包括滚流比、湍动能、喷雾图像、混合气浓度分布、燃油湿壁量。研究结果表明:在发动机2 000r/min全负荷工况下,两个方案缸内流场差异较小,混合气分布差异明显;二次喷射策略会降低燃油湿壁,燃油湿壁量最大值降低了27%。通过台架试验得到通过二次喷射策略机油稀释比例降低了15%,早燃频次也有所下降。

By numerical simulation method, the process of in-cylinder fuel injection, mixture formation and wall wetting was studied, with a focus on two-stage injection to reduce wall wetting. The simulation results of single injection case are compared with those of tow-stage injection case in terms of tumble ratio, turbulent kinetic energy, spray pattern, mixture distribution（volume fraction vs. lambda）, and stuck droplet mass on cylinder liner. The simulation results show that at engine full load of 2 000 r/min, the difference of in-cylinder flow between the two cases is small, the difference of mixture distribution between the two cases is obvious, the two-stage injection strategy can reduce wall wetting, and the maximum value of stuck droplet mass is reduced by 27%. The results of a bench test show that oil dilution is reduced by 15% and pre-ignition frequency is reduced too with the tow-stage injection strategy.