直喷汽油机缸内喷雾湿壁问题研究

Investigation on Wall Wetting for GDI Engine

直喷汽油机的湿壁问题会导致机油稀释,燃油经济性下降及尾气排放增加。但通过喷雾、燃烧室及缸内流场三者合理匹配与优化可以大大减少燃油湿壁。利用激光诊断技术对某直喷喷油器的喷雾特性进行全面测试,然后标定三维CFD软件中的喷雾模型,对缸内喷雾和混合气形成过程进行仿真计算,并研究了燃油喷射策略对燃油湿壁的影响。研究结果表明:采用两段喷射策略可以降低15%的碰壁量,混合气均匀程度基本不变;采用三段喷射可以降低27%的碰壁量,并可明显改善混合气浓度分布。

Spray impingement on piston and cylinder walls in gasoline direct injection （GDI）engine results in lubricant dilution, high fuel consumption rate and undesired emissions. Optimal matching among spray characteristics, combustion chamber shape and air flow field may reduce significantly the impingement problem. The spray characteristics of a 6-hole GDI injector were measured with laser diagnostics technology, spray model in 3D CFD software was calibrated in a spray bomb and air-fuel mixture formation in cylinder was simulated, and effect of fuel injection strategy on fuel impingement was examined. Results show that dual-injection strategy can reduce the impingement by 15% with mixture homogeneity unchanged basically, and triple-injection strategy can reduce the impingement by 27% and improve obviously mixture concentration distribution.