缸内直喷汽油机低速混合气形成过程研究

通过Hydsim搭建的多孔喷油器一维仿真模型分析了针阀开启与关闭阶段喷油参数的变化，并使用FIRE软件对15 MPa喷油压力下的定容室喷雾进行了数值模拟及模型标定. 在此基础上，以一涡轮增压缸内直喷汽油机为研究对象，对比数值模拟与实验结果，分析了滚流比及喷油时刻对低速工况缸内混合气形成过程的影响. 结果表明，对2000 r/min全负荷工况，采用较高滚流比可增强缸内气流运动，促进燃油快速蒸发并形成更加均匀的混合气，而适当的喷油时刻可减少燃油碰壁，改善混合气浓度分布，从而更利于燃烧及发动机性能的提升. 

Study on Low-Speed Mixture Formation Process of a Gasoline Direct Injection Engine

With the 1D simulation model of a multi-hole injector which was constructed by Hydsim code, the injection parameters during the needle opening and closing at different pressure were studied,then the spray formation at 15 MPa injection pressure was simulated by FIRE and its numerical model was validated in a constant volume bomb. Based on this, the influence of tumble ratio and injection timing on low-speed mixture formation process for a turbocharged gasoline direct injection engine was analyzed. The result showed, for full load and 2000 r/min, the higher tumble ratio can strengthen cylinder air flow, subsequently the faster evaporation of fuel and the more uniform mixture can be achieved, meanwhile the appropriate start of injection can decrease fuel impingement and also improve the distribution of mixture concentration, all of these are better for improvement of combustion and engine performance.