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Direct-injection spark-ignition engines are becoming popular nowadays in automobiles because of their low fuel economy and exhaust emissions. They operate with a lean stratified mixture in most load conditions. However, their entire performance and emissions are dependent on stratification at different load conditions. In fact, stratification in these engines depends upon in-cylinder flows and air-fuel interactions, which in turn dependent on combustion chamber shape, compression ratio and engine speed etc. Among them, combustion chamber shape plays an important role and hence understanding its effect is very much essential to optimize its configuration in these engines. Therefore, in this study, a CFD analysis using a commercial software has been carried out with different combustion chamber shapes formed by using different piston top profiles in a two-valve four-stroke engine.

Nowadays, Direct Injection Spark Ignition (DISI) engines are very popular because of their lower fuel consumption and exhaust emissions due to lean stratified mixture operation at most of load conditions. In these engines, achieving mixture stratification plays an important role on performance and emission characteristics of the engine. Also, mixture stratification is mainly dependent on in-cylinder flows and air-fuel interaction, which in turn largely dependent on valve configurations. Therefore, understanding them is very much essential in order to improve the engine performance. In this study, a CFD analysis has been carried out on two- and four-valve four-stroke engines to analyze in-cylinder flows and air-fuel interaction at different conditions. The engines specifications considered here are taken from the literature for which experimental data is available. ‘STAR-CD’ software has been used for the CFD analysis. For meshing, polyhedral trimmed cells have been adopted.