Numerical simulation study of spray wall impingement and adhered fuel film under different altitude conditions during cold start of diesel engines

Diesel engines operating under high-altitude cold start conditions are more susceptible to fuel spray wall impingement, which leads to the formation of adhered fuel films. This phenomenon can result in fuel film combustion and pool fires, causing erosion of the pistons, increasing thermal load, and generating excessive soot. However, the detailed mechanisms of spray impingement and the formation of adhered fuel films at high altitudes remain inadequately understood. In this study, simulations were conducted to investigate the formation of adhered fuel films from spray wall impingement under varying altitude conditions during the cold start of a diesel engine. The results show that as altitude increases, the fuel–air mixture tends to shift toward lower temperature and lower concentration regions. The peak mass of the ignitable fuel–air mixture decreases with altitude, showing reductions of 22.22 % at 4000 m and 55.68 % at 6000 m relative to sea level. Concurrently, the mass of adhered fuel film increases with altitude, with the proportion of fuel adhering to the wall rising from 46.27 % at sea level to 64.88 % at 6000 m. At an altitude of 4000 m, liquid-phase fuel spray wall impingement becomes the dominant mechanism, altering the direction of heat transfer and significantly increasing the mass of adhered fuel. Due to the increased thickness of the fuel film at higher altitudes, its evaporation rate decreases. Moreover, heat flux density decreases with altitude, further declining with distance from the spray center. At 4000 m, the heat flux density becomes negative, reaching −1.5 MW/m² at 6000 m. These results offer critical insights into spray-wall interactions and fuel film dynamics under high-altitude conditions, providing a theoretical foundation for optimizing diesel engine performance in such environments.