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. In-cylinder flows have been predicted by solving mass, momentum and energy equations by using SIMPLE algorithm. Air-fuel interaction has been predicted by solving droplet breakup, droplet-wall interaction and atomization models. The CFD results are compared with available experimental data.
From the analysis of results, it has been found that four-valve engine configuration gives better in-cylinder flows and equivalence ratio near spark plug. Also, from the analysis, it is possible to obtain best possible combustion chamber geometry for DISI engine.