缸内直喷发动机快速起动首循环喷雾的数值模拟

Numerical Simulation of First Cycle Spray during Quick Start for In-cylinder Direct Injection Engine

基于某缸内直喷(GDI)发动机建立了三维模拟平台,并对喷雾模型进行了验证,进而对GDI发动机起动时第2缸的喷雾和混合气形成进行了数值模拟,分析了不同喷油策略下压缩上止点时混合气的空燃比分布和着火情况,并与试验结果进行了对比分析。研究结果表明:喷油时刻距离上止点相对较远或者在上止点附近时,混合气在压缩上止点倾向于自燃;若混合气偏稀,即使喷油时刻在距离上止点相对中间的位置时,混合气仍倾向于自燃。通过试验结合数值模拟的方法,分析并指出了第2缸在不同喷油策略下发生自燃、可以点燃和失火的区域。

The 3D simulation platform for a gasoline direct injection （GDI） engine was established, the spray model was verified, and the spray and gas mixture formation of the second cylinder during engine start was simulated. The air-fuel ratio and ignition condition at top dead centre （TDC） under different injection strategies were analyzed and compared with experimental results. The results show that the compressed mixture is easy to ignite spontaneously when the injection timing is relatively far from or is close to TDC. The lean mixture is still inclined to ignite spontaneously even though the injection timing is relatively middle from TDC. Through the test and numerical simulation, the areas of auto-ignition, ignition and misfire for the second cylinder are finally determined under different injection strategies.