进气门关闭状态下喷油时刻对汽油机性能的影响

为了改善进气道喷射式发动机性能，采用台架试验和数值计算的方法对喷油时刻与进气道喷射式汽油机性能之间的关系进行了研究。研究结果表明：在进气门关闭状态下进行燃油喷射，发动机运行工况不同，喷油时刻对发动机性能的影响规律不同，小节气门开度时推迟喷油时刻会导致 HC 排放升高和发动机动力性下降，大节气门开度时喷油时刻的改变对发动机性能的影响可以忽略。通过数值计算分析发现该变化规律与附壁油膜挥发速率有直接关系，在小节气门开度条件下，附壁油膜无法完全挥发，会增加燃油以液态形式进入气缸的量，从而使发动机性能下降，而处于大节气门条件下，较高的机体温度使得附壁油膜挥发速率加快，降低液态燃油的量，从而改善发动机性能。因此，进气道喷射发动机可以在小节气门开度时采用两次燃油喷射方式提升发动机性能，而在大节气门开度下则无需考虑喷油时刻的影响。

Effects of Fuel Injection Timing on Performance of Gasoline Engine under Intake Valve Closing

In order to improve the performance of port fuel injection (PFI) gasoline engine ,the relationship between the injec‐tion timing and engine performance was studied through the bench test and numerical simulation .The results show that the fuel injection timing has different influences on engine performance under different operating conditions when the intake valve is close .The retarded injection timing will result in the increase of HC emission and the decrease of engine performance at a small throttle opening ,but has little influence on engine performance at a large throttle opening ,which depends on the evaporation rate of wall‐adhered fuel film according to the numerical calculation and analysis .The wall‐adhered fuel film cannot evaporate completely so as to increase the liquid fuel amount inside cylinder and thereby the engine performance deteriorates at a small throttle .On the contrary ,higher body temperature accelerates the evaporation of fuel film so as to reduce the liquid fuel and thereby the engine performance improves at a large throttle .Accordingly ,the dual fuel injection method should be applied in order to improve engine performance only at small throttle opening .