Study of Diesel Spray Impinging Ignition and Combustion Characteristics Under Variable Ambient Densities Based on the Visualization Experiment

The application of turbocharged intercooler direct injection (DI) diesel engine in large diesel vehicle transportation and construction machinery will be indispensable for a long time in the future. The extreme condition of the plateau has become a hotspot in the research of diesel combustion. When the diesel engine works on the cold-start or low-load/low-speed condition, the problems of combustion and emission caused by abnormal supercharging of a turbocharger are apparent. The development of the miniaturization of diesel engines can effectively avoid liquid-wall impingement. However, the low density of the plateau will bring inevitable combustion modes, such as impinging ignition and combustion. This study summarized the relationship among spray, fuel–air mixing, ignition, soot formation, and ambient density under the condition of impinging ignition and nonliquid spray impingement, providing a reference for the further research and improvement of diesel engine combustor structure design. The effect of ambient density change on diesel spray mainly weakens radial air entrainment in the fuel injection. There was apparent impinging ignition at 11.37 g/m³ density, and the ignition time delay was 0.2 ms longer than that at 16.07 g/m³, corresponding to the 0 m altitude. Under high altitude with more significant density, the combustion is more intense under higher temperature. However, the larger flame diffusion area under low density leads to the larger soot distribution area and more considerable soot generation.