The computational fluid dynamics (CFD) simulation to investigate the effect of piston crown shape to air motion characteristics of an internal combustion engine is presented in this paper. The in-cylinder air motion before the fuel injection event plays an important role to the generation of swirl and tumble flows due to the high turbulence during the intake and compression strokes. Swirl is generated by the suction of air flow into the combustion chamber during the intake stroke and greatly enhances the mixing of air and fuel to yield either a homogeneous or stratified mixture inside the cylinder. On the other hand, tumble plays an essential role in producing the compression ratio required for rapid combustion process. The characteristics of swirl and tumble flows inside cylinder of engine can be expressed in the form of swirl and tumble ratios. Two different piston crown shapes for homogeneous and stratified are carried out to determine the swirl and tumble ratio generated inside engine cylinder for selected events based on crank angle. The simulation was performed from the beginning of the intake stroke until a moment in the compression stroke just before the fuel injection process begins. Swirl and tumble ratios obtained from the simulation will determine the optimum piston crown to be used for better air motion features and combustion to gain the optimum operating condition for such engine.
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