缸内直喷汽油机工作过程三维数值模拟

摘要

This paper aims to analyze the working process of a gasoline direct injection engine.Using the 3D CFD simulation tool, the working fluid in intake ports and cylinder, the processes of fuel injection and fuel-air mixing were simulated.The formation and development processes of tumble in cylinder, and the influence of tumble on fuel-air mixture formation were investigated.Comparisons on fuel injection, fuel-air mixing and combustion at two injection timings were made.Results show that the injection strategy with SOI of 420° CA gives the superior fuel-air mixing quality around the spark plug at ignition timing than the strategy with SOI of 390° CA does due to the improvement in ignition and flame propagation.To further improve the mixture quality, configuration on piston crown was optimized and analysis on mixture formation processes of the new configurations was made.Simulation results indicate that the new configurations have faster fuel vaporization rate and better mixture homogeneity.%用三维CFD数值模拟软件对一台均质充量缸内直喷汽油机全负荷工况时的进气、压缩和混合气形成过程进行了三维瞬态数值模拟.分析了进气道内及气缸内的工质运动状态,研究了缸内滚流的形成和发展历程及其对混合气形成的影响,探讨了两种喷油定时所对应的燃油喷雾、混合气形成过程.结果显示,在现有条件下喷油开始时刻为420°CA所对应的点火时刻火花塞附近混合气形成质量好于喷油开始时刻为390°CA的情况,更利于着火和火焰传播.另外,为了进一步改善混合气质量,改进了燃烧室设计方案,并对新方案的混合气形成质量进行了对比分析.结果表明,与原方案相比新燃烧室方案的燃料蒸发速度更快,混合气均匀性更好.