海拔高度对柴油机缸内热流分布影响规律研究

为了分析高原环境下柴油机缸内热流分布变化规律，采用计算流体动力学方法对不同海拔高度条件下的柴油机燃烧过程进行了三维数值模拟研究。结果表明：考虑燃气向缸壁传热的燃烧过程计算时，壁面函数采用Han-Reitz模型可以得到满意结果；随着海拔高度升高，过量空气系数降低，滞燃期延长，着火推迟，燃烧恶化，爆压降低，燃烧温度升高；海拔高度越高，喷雾贯穿动量越大，壁面换热系数增长速度越快，在上止点后气体流动性对换热系数的影响所占比重增大，而进气流量对换热系数的影响比重降低，换热系数随着海拔高度升高而增大；在换热系数、壁面燃气温度和壁面油膜燃烧影响下，高海拔燃烧时壁面平均热流大幅度增大，海拔高度从1 000 m升高到4 500 m 后，缸盖和活塞瞬时平均热流最大值增幅分别达到30%和26%.

Effect of Altitude on Distribution of In-cylinder Heat Flux

The computational fluid dynamics (CFD) method is adopted to study the change rule of heat flux distribution in plateau environment. Three-dimensional numerical simulation of combustion process of diesel engine at different altitudes was carried out. The results show that the Han-Reitz model can be used to obtain the satisfied results when the combustion process is calculated, including the process of combustion gas transferring heat to cylinder wall. With the increase in altitude, the excess air coefficient decreases, the ignition delay period is prolonged, the ignition delays, the combustion is deteriorated, the explosion pressure decreases, and the combustion temperature rises. The higher the altitude is, the greater the spray momentum is. The influence of gas flow on the heat transfer coefficient increases after top dead center, and the effect of air intake flow on the heat transfer coefficient decreases, and the heat transfer coefficient increases with the increase in altitude. Under the influences of heat transfer coefficient, gas temperature of wall and wall oil film combustion, the average heat flux on the wall increases greatly during combustion at high altitude, and the instantaneous average heat flux on the wall increases from 1 000 m to 4 500 m, and the instantaneous average heat fluxes on the cylinder head and piston increase to 30% and 26%, respectively.