发动机排气喷雾降温数值模拟与影响因素分析

Simulation on water spray cooling in engine exhaust gas and its influencing factors

针对发动机排气喷雾降温问题,基于气-粒两相流理论建立了排气系统内喷雾降温的数学模型,用计算流体动力学方法进行数值模拟,揭示雾滴运动规律和排气降温规律,分析喷雾参数对发动机排气喷雾降温效果的影响。研究发现,喷雾流量、喷雾锥角和雾滴平均直径对排气喷雾降温的影响较大,雾滴的初始温度、最大直径及其尺寸分布的均匀度指数等因素对排气喷雾降温影响较小;提高发动机排气喷雾降温效果,需要将雾滴尺寸控制在一定的分布范围之内,而不能一味减小雾滴平均直径。数值模拟结果与实验结果符合较好。

For the problem of water spraying into the high temperature of the engine exhaust gas,the mathematical model was proposed based on the gas-particle two-phase flow theory,and the numerical simulation was performed using CFD method.The movement law of the water droplets and the cooling law of the exhaust gas were obtained.And the influences of the water spray parameters on the gas outlet temperature were investigated.It is found that the droplet mean diameter,the flow rate and the spray angle of the nozzle have a strong influence on the gas spray cooling,while the initial temperature,the maximal diameter and the size dispersion coefficient of the droplet is not evident.For the purpose of promoting the gas spray cooling effect,the droplet size distribution should be in an appropriate range,while the droplet mean diameter should not be decreased blindly.The predicted results are in good agreement with the experimental results.