Effects of operating parameters on in-cylinder flow characteristics of an optically accessible engine with a spray-guided injector

This study investigated the cycle-to-cycle variation of a spark-assist high-compression-ratio spray-guided direct-injection two-cylinder optically accessible engine. The cycle-to-cycle variation was evaluated by calculating the mean velocity, tumble ratio, tumble center, and effective radius using the PIV measurement results. Under all experimental conditions, the mean velocity continuously decreased owing to the momentum loss from the intake to compression strokes. A low COV was observed within the high-velocity region, and the effective radius decreased as rotational flow formed regardless of the engine operating conditions. As the engine speed increased, owing to the high piston speed, the in-cylinder flow intensified. However, the effective radius and tumble ratio were similar during the compression stroke. As the intake pressure increased from 0.8 to 1.3 bar, the mean velocity and tumble ratio slightly increased. Moreover, the effective radius decreased slightly during the compression stroke. As the IVO timing was retarded, during the intake stroke, the structure of the in-cylinder flow changed dramatically. Rapid momentum dissipation occurred after the intake air inflowed strongly, resulting in relatively weak rotational flow compared to the reference and advanced IVO timing conditions. •Visualization of the in-cylinder flow in high-pressure spray-guided DI engine.•Investigation of cycle-to-cycle variation depending on engine operating parameters.•Influences of fuel injection on cycle-to-cycle variation and in-cylinder flow.•The cycle-to-cycle variation of in-cylinder flow decreased as the fuel was injected.