柴油机冷起动工况附壁油膜生成特性研究

Study on Characteristics of Wall-wetting Fuel Film of Diesel Engine During Cold Starting

柴油机冷起动时缸内压缩上止点的温度和密度低,喷雾撞壁量大,且形成的油膜蒸发缓慢,在后续燃烧过程中极易产生池火,不利于碳烟排放控制。本研究在流动式定容燃烧弹中结合背光法和折射率匹配法,研究了柴油机冷起动过程中不同环境温度和密度对附壁油膜生成特性的影响。研究表明环境温度对附壁油膜面积、体积和厚度分布的影响较大,环境温度为500 K时附壁油膜的峰值体积为600 K时的6倍,高环境温度下油膜厚度减小且分布趋向于均匀,600 K条件下不同厚度油膜占比均低于15%。不同环境密度工况下,附壁油膜的蒸发速率较为稳定,高环境密度会促进油膜的蒸发。

The temperature and density of the top dead center in the cylinder of the diesel engine are low, the amount of the spray impinges the wall is large, and the fuel film evaporates slowly,so it is easy to produce pool fire during the combustion, which is not conducive to the control of soot emission. In this paper, the influence of different ambient temperature and density on the characteristics of the fuel film during the cold starting of diesel engine is studied by combining the backlight method and the refractive index matching method in the flow constant volume combustion bomb. The results show that the environmental temperature has a great influence on the area,volume and thickness distribution of the fuel film. The peak volume of the fuel film when the ambient temperature is 500 K is 6 times of that when the ambient temperature is 600 K, the fuel film thickness decreases and the distribution tends to be uniform at high ambient temperature, and the proportion of the fuel film with different thickness is less than 15% at 600 K. Under different environmental densities, the evaporation rate of the fuel film is relatively stable, and high density will promote the evaporation of the fuel film.