Effects of swirl enhancement on in-cylinder flow and mixture characteristics in a high-compression-ratio, spray-guided, gasoline direct injection engine

In this study, the flow enhancement effects of applying a swirl control valve were investigated with particle image velocimetry and simulation using CONVERGE v2.4 program in a high compression ratio, spray-guided, gasoline direct injection engine. This was followed by analysis of varying the spray structure and the mixture preparation process for different swirl control valve angles. The flow intensity was strengthened in the order of swirl control valve angle 45°, 30°, and 0°, and spark plug gap velocities near TDC were increased 1.89, 4.40, and 6.69 m/s in that order. However, the effect was not significant when it was increased to more than 45°. Also, the swirl-dominant flow and the tumble-dominant flow were differentiated based on the relationship between maximum swirl and tumble ratios. In the swirl dominant flow (swirl control valve angle of 0°), more retarded injection timing produced mixture formation in the order of homogenous to mal-distributed to stratified, whereas in the tumble dominant flow (swirl control valve angle of 45°), the order was homogenous to stratified to mal-distributed. It was determined by characteristic period to which the injection timing belonged, and the characteristic period was defined based on the relationship between the intake valve lift and the piston velocity.