Effect of altitude on the split injection combustion process of diesel impinging spray

Diesel engines at high altitudes produce large amounts of soot due to low air densities. Understanding the ignition and combustion processes of diesel engines under high-altitude operating conditions is crucial for reducing soot emissions from diesel engines in plateau areas. This paper focuses on the effect of split injection mass and injection interval on diesel ignition and combustion characteristics at three altitudes (0 m, 3000 m, and 4500 m). The results show that no matter whether the first injection is small or large, and the injection interval is long or short, the liquid penetration is almost the same at high altitude. At an altitude of 4500 m, the liquid fuel impinges the wall to form a wet wall, producing a small amount of soot but many unburned hydrocarbon (UHC) emissions. The soot from the combustion of the first injection decreases with altitude. The maximum soot net oxidation rate after the last soot peak decreases with increasing altitude. The increase in altitude results in a smaller change in the rate of soot net oxidation. For the three split injection strategies, the proportion of high- concentration soot varies differently at different altitudes. This paper also discusses the change in soot mass and flame area at 0.2 ms after the end of injection (AEOI) to obtain the change in high concentration soot.