Abstract:

The in cylinder processes of an automotive turbocharged common rail diesel engine using close post fuel injection strategy under high load conditions were numerically computed by means of the 3D CFD software FIRE. The effects of the close post injection fuel amount and the interval between the main and the post fuel injections  on the combustion process were analyzed. The computed results show that with the increase of the post injection fuel amount and the injection interval, the in cylinder maximum combustion pressure and temperature as well as the heat release rate reduce, the centroid of the heat release rate diagram shifts backward, and all these result in less NOx emissions and worse fuel economy. The increase of the post injection, on one hand, enhances the penetration of fuel spray, increases the fuel vapor in the high temperature oxygen insufficient region near the combustion chamber wall, so enhances the soot generation, on the other hand, the post injection strengthens the disturbance effect to the flow field, may entrain more oxygen into the combustion product zone and accelerates the oxidation of generated soot. So, appropriate selection of the post injection amount may result in lower soot emission. When the interval between injections too large, there is an obvious rising trend of soot emission.

Key words: power machinery and engineering, common rail diesel engine, closed post injection, combustion, simulation calculation