扫气道对二冲程直喷汽油机扫气和喷雾过程影响的多维数值模拟

Multi-Dimensional Simulation of Effects of Scavenge Ports on Scavenge and Spray Processes in Two-Stroke GDI engines

针对实际工况，运用CFD软件FireV8．5，对3种扫气道形式的扫气和喷雾过程进行了模拟。结果表明，利用双扫气道可提高喷雾初期缸内平均温度，特别是气缸上方局部温度；沿气缸轴线上下的高速气流促使部分液滴更早到达活塞顶，同时液滴整体在缸内分布更广，因而燃油蒸发加快，混合气更均匀。五扫气道滚流比最大，混合气均匀性也比滚流较弱的三扫气道好，但其流场和温度场分布不如双扫气道对燃油蒸发和形成均质混合气有利。4500r／min的试验结果表明，在中到高负荷，双扫气道的制动有效碳氢排放比三扫气道降低11％～18．7％，制动有效燃油消耗率降低约5％，在节气门全开时由于充气效率下降，其最大功率比三扫气道略低。

Scavenge and spray processes in three different scavenge ports were simulated by using CFD software Fire V8.5. The results show that ＂dual scavenge ports＂ gets higher in-cylincler mean and local tem- perature, a part of spray droplets reach the piston top earlier due to rapid perpendicular in-cylinder flow, and spray droplets diffuse more fastly in the cylinder. So ＂dual scavenge ports＂ can result in faster fuel evapora- tion and more homogenous air fuel mixture. ＂Five scavenge ports＂ has the highest tumble ratio and gets more homogenous mixture in comparison to ＂three scavenge ports＂ which produces relatively weaker tumble, but its in-cylinder flow and temperature distribution are inferior to ＂dual scavenge ports＂ which is benefical to the fuel evaporation and the formation of homogenous mixture. Test results show that at4500r/min, under mid- dle to heavy load, the brake specific hydrocarbon emission （BSHC） and brake specific fuel consumption （BSFC） when using ＂dual scavenge ports＂ reduce by 11%-18.7% and 5% respectively in comparison to ＂three scavenge ports＂, and the maximum power at full throttle when using ＂dual scavenge ports＂ is slightly lower than when using ＂three scavenge ports＂.