Cycle-to-Cycle Analysis of Swirl Flow Fields inside a Spark-Ignition Direct-Injection Engine Cylinder Using High-Speed Time-Resolved Particle Image Velocimetry

The cycle-to-cycle variations of in-cylinder flow field represent a significant challenge which influence the stability, fuel economy, and emissions of engine performance. In this experimental investigation, the high-speed time-resolved particle image velocimetry (PIV) is applied to reveal the flow field variations of a specific swirl plane in a spark-ignition direct-injection engine running under two different swirl air flow conditions. The swirl flow is created by controlling the opening of a control valve mounted in one of the two intake ports. The objective is to quantify the cycle-to-cycle variation of in-cylinder flow field at different crank angles of the engine cycle. Four zones along the measured swirl plane are divided according to the positions of four valves in the cylinder head. The relevance index is used to evaluate the cycle-to-cycle variation of the velocity flow field for each zone. It is based on comparing the flow similarity of field fields of the same crank angle from different cycles. A comparison of relevance index for each zone between intake and compression strokes is made. The result shows the difference of cycle-to-cycle variation in each zone is affected by the motions of piston and intake valves. The cycle-to-cycle variations of flow field during intake stroke are higher than that during compression stroke, and the variations seem to be less pronounced under the high swirl condition where the flow is more directed in the cylinder.