CFD study and experimental investigation of piston geometry induced in-cylinder charge motion on LPG fuelled lean burn spark ignition engine

Abstract

The performance and emission characteristics of LPG fuelled SI engine is determined by efficient combustion. This depends on the in-cylinder motion of intake homogenous charge generated by combustion chamber geometry. The inherent, unsteady, turbulent motion of the mixture helps in flame propagation which in turn enhances the combustion rate. Compression ratio, charge squish velocity and turbulent kinetic energy are responsible for stable combustion and laminar flame propagation. The in-cylinder charge motion is generally described by swirl, squish, tumble and turbulence which have a vital role on air-fuel mixing and combustion. The piston geometry helps in aiding in-cylinder motion for reducing fuel consumption and enhancing the combustion parameters. In particular, piston squish area in combustion chamber geometry has a major influence in charge motion inside the combustion chamber. The effect of piston squish area on charge motion was studied by CFD using STAR-CD with 25%, 30%, 35% and 40% squish areas to optimize piston crown geometry. Experiments were also conducted with above squish area pistons at a compression ratio of 10:1 to validate the CFD study. It was found that 30% piston squish area improved the performance, combustion characteristics and reduced the emission with LPG fuelled lean burn SI engine.