| Abstract:In order to solve the combustion deterioration and emissions increase of heavy duty diesel engines under transient conditions, the study of the influence of the fuel post injection on transient performance was carried out on a heavy duty vehicle diesel engine with 8.6 L displacement, and the influence and its mechanism of the fuel post injection on combustion process, air flow and soot emissions were analyzed by simulation. In order to better illustrate the mixing process of mixture in the cylinder, the concept of oxygen driven energy was introduced thereafter. Results show that in the main injection stage, the oxygen driven energy plays a leading role in the formation of in-cylinder mixture, With the increase of the amount of fuel post injection the in-cylinder disturbance increases, resulting in an increase in the ratio of lean mixture which makes the second and third peak of heat release rate enhance and the combustion phase advance, but the amount of fuel post injection has little influence on the NOx emissions. In view of the combined consideration of thermal efficiency and soot emissions, the use of an interval of 4° crank angle between the main and post injections and amount of 25% post injection has a best emission effect at 90% load and under transient conditions. |