Study on the Effects and Mechanisms of the Micro-Explosion of Impinging Diesel Fuel Droplet on the Structure Damage of the Combustion Chamber

Fuel spray impingement is a common phenomenon during the combustion processes of a DI diesel engine. When liquid droplets impinge on the hot surface of a combustion chamber, a complex heat transfer and mechanical interaction occur between the droplets and combustion chamber. This probably changes the surface topography and microstructure of the impact position. Based on the experimental method, the fuel spray phenomenon and conditions of a surface pit caused by droplet impingement were investigated. The experimental results indicate that the surface pit is formed under specific conditions, i.e., a specific droplet diameter and surface temperature. Scanning electron microscopy of the pit area shows that the microstructure of the pit changed from an original dense and smooth surface to a loose structure. The microstructure of the pit did not show a molten state. The concentration of metal and nonmetallic elements in the pit area changed significantly. According to large-eddy simulation, microbubbles are formed in the impingement droplet. Bursting of bubble can lead to violent pressure, velocity, and temperature fluctuations. This can also cause water hammer effect, inducing a strong instantaneous impact and forming micropits in the combustion chamber.