CFD Study of an LPG DI SI Engine for Heavy Duty Vehicles 2002-01-1648

This work aimed to develop an LPG fueled direct injection SI engine, especially in order to improve the exhaust emission quality while maintaining high thermal efficiency comparable to a conventional engine. In-cylinder direct injection engines developed recently worldwide utilizes the stratified charge formation technique at low load, whereas at high load, a close-to-homogeneous charge is formed. Thus, compared to a conventional port injection engine, a significant improvement of fuel consumption and power can be achieved. To implement such a combustion strategy, the stratification of mixture charge is very important, and an understanding of its combustion process is also inevitably necessary.

In this work, a numerical simulation was performed using a CFD code (KIVA-3), where the shape of a combustion chamber, swirl intensity, injection timing and duration, etc. were varied and their effects on the mixture formation and combustion process were investigated. The conclusions include the fuel injection conditions such as injection timing and duration showed relevant influences on the stratification of mixture charge. Moreover, it was also clarified that the in-cylinder flows such as swirl and tumble significantly enhance the mixture formation process, forming a rich charge around the spark plug and a lean one near the cylinder wall. This eventually leads to the improved emission characteristics in an LPG direct injection SI engine.