Effect of combustion chamber shape on in-cylinder flow and air-fuel interaction in a direct injection spark ignition engine - A CFD analysis

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. The engine specifications and piston top profiles have been taken from the literature for which experimental data is available for comparison. From the analysis, it is observed that, combustion chamber shape with pentroof-offset-bowl piston gives about 221.5% higher tumble ratio and about 59.5% higher turbulent kinetic energy of in-cylinder flows, and about 6.8% higher percentage of fuel evaporation as compared to those of dome piston. Therefore, combustion chamber shape with pentroof-offset-bowl piston is better suited as compared to other combustion chamber shapes.