二甲基醚喷雾混合过程的计算研究

Numerical study of the DME spray mixing process

采用气相射流模型对二甲基醚的喷雾特性进行了模拟计算 ,并将其与柴油喷雾的模拟计算值进行了对比 .结果表明 ,在喷孔直径、环境密度等参数相同的条件下 ,二甲基醚喷雾的轴心速度和浓度的衰减速率均大于柴油喷雾的 ,而二甲基醚喷雾的贯穿距离与锥角则分别小于和大于柴油喷雾的 .当环境密度和喷孔直径改变时 ,DME喷雾的轴心速度、贯穿距离和喷雾锥角均会随之变化 .模拟计算结果与实验观测结果基本相符 .

A mathematical model was developed for the prediction of the dimethyl ether (DME) spray characteristics. The model for DME spray was treated as a turbulent quasi-steady gas jet because of its much lower boiling temperature, rapid evaporation rate and the effect of air swirl taken full account. It consisted of the equations written in an integral form of the conservation of the mass and momentum. It can be used to calculate the main parameters of DME spray such as spray penetration, trajectory and mixing rate of DME with ambient air. The DME spray behavior under engine-like conditions was calculated and the differences between DME and diesel fuel were analyzed for the same nozzle hole diameter and ambient pressure. The results showed that the decline rate of centerline velocity and concentration of DME spray was higher than that for diesel fuel spray. The penetration of the DME spray was smaller and its cone angle was lager than that for the diesel fuel spray. The effects of the ambient air pressure and the nozzle hole diameter on the DME spray characteristics were the same as they were on the diesel fuel spray. Good agreement existed between the experimental data and calculated results.