Numerical simulation of stratified lean burn for LPG engine

摘要

Liquefied petroleum gas (LPG) has been considered one of the excellent alternative vehicle fuels for its lower fuel cost and lower emissions compared with traditional petroleum fuels; however under part load the fuel economy is bad. The lean burn is one of the powerful methods for improving fuel economy under part load which can improve the thermal efficiency by 10%∼15%. Because mixture formation process has significant effect on combustion and emissions of the engine, especially on the organizing combustion process, it is very necessary and important to understand the LPG''s mixture formation in order to optimize the combustion and reduce the emissions. Therefore, based on the modified model, the spray process of the liquid phase LPG is studied by numerical method. The spray model is validated by comparison with the results of simulation and experiment first. Then the feasibility of stratified lean burn for LPG engine is studied through numerical analysis method. And the LPG engine with inflexion intake manifold, the partition in the intake manifold, the concave piston and injection during the later period of intake stroke is employed. The results indicate that under the effect of vertical tumble stratified mixture distribution is formed. There is dense mixture around the spark plug meanwhile sparse mixture far from it, and between the dense and sparse zones is the naturally stratified mixture.