Numerical Study on Turbulent Diffusion Combustion Flame Lift-off Length in a Direct Injection Diesel Engine

摘要

The spray and combustion processes of a DI diesel engine were simulated with a multi-dimensional CFD model, and the simulated in-cylinder pressure was in good agreement with the measured one. The flame lift-off length was determined by the stabilized distance between the high temperature zone and the nozzle exit, and the influences of different intake gas conditions on the flame lift-off length were investigated. The CFD model successfully predicts that the flame lift-off length tends to decrease as the initial intake gas pressure is increased. And with the increase in the intake gas temperature, the flame lift-off length presents a tendency to increase first and decrease afterwards. The model was also applied to simulate the combustion process of the diesel engine under different EGR rate conditions, and the computational results show that both the flame lift-off length and the auto-ignition delay time are increased with the increase in EGR rates.