基于Converge的柴油机起动过程喷雾撞壁仿真分析

柴油机起动过程中,转速、缸内背景压力及温度偏低会导致喷雾撞壁,影响燃油雾化效果。利用三维计算软件Converge,采用组合喷雾模型及B-G撞壁模型建立了燃油喷雾撞壁模型,并利用可视化定容弹喷雾撞壁试验系统验证了模型的准确性。基于建立的喷雾撞壁模型,研究分析了缸内背景压力、壁面干湿状况及壁面粗糙度对某型柴油机喷雾撞壁的影响规律,仿真结果表明：随着缸内背景压力下降,撞壁时刻提前,扩散距离增大,油膜产生时刻提前,油膜厚度增大；活塞顶壁面粗糙度增加,喷雾油束撞壁后扩散距离减小,附壁油膜厚度增大；当活塞顶壁面为湿壁时,喷雾油束撞壁后扩散距离增大,附壁油膜厚度下降。研究为燃烧室、喷油系统等优化设计提供了参考。

Simulation Analysis of Spray-Wall Impingement on Diesel Engine Starting Process based on Converge

During the starting process of diesel engine, the low speed, cylinder pressure and temperature lead to spray-wall impingement and affect the fuel atomization effect. By using three dimensional calculation software Converge, the Spray-wall impingement model is established with adopting the combination of fuel spray model and B-G collision model. To verify the accuracy of the model, the visualization of constant volume bomb spray wall impinging system is designed. Based on the established Spray-wall impingement model, the influence of the background cylinder pressure, the dry and wet condition of the wall and the wall roughness on the spray wall collision of a diesel engine is simulated and analyzed. The simulation results show that: as the background cylinder pressure decreases, the collision and the oil film generation time is advanced, the diffusion distance is increased and the oil film thickness is increased. With the increase of the piston top wall roughness, the diffusion distance decreases and the oil film thickness increases. When the top wall of the piston is wet, the diffusion distance of spray oil beam increases after hitting the wall, and the oil film thickness decreases. The research provides reference for the optimized design of combustion chamber and oil injection system.