Numerical study of fuel spray and mixture formation in a spark ignition engine with asynchronous intake valve timings

The influences of asynchronous intake valve timings on in-cylinder flow motions and mixture formation in a four valves single cylinder port fuel injection engine operating with iso-octane were examined using computational fluid dynamics. First, the predicted spray characteristics from numerical modeling were validated against experimental results, and showed good agreements. Transient full cycle simulations were then carried out at 6000 rpm, wide open throttle condition. Three cases named “Advance 10”, “Baseline”, and “Retard 10”, which correspond to 10 ^oCA advancement, no change, and 10 ^oCA retardment of one intake valve opening and closing, respectively, were simulated. With asynchronous valve timings, swirl ratio, side-way tumble ratio of the charge motion were significantly increased comparing to the synchronous case. During intake and compression strokes, the average turbulent kinetic energy was improved by 5.49% with 10^o valve timings advancements, and 8.4% with 10 ^oCA delay. Retard 10 case resulted in the most homogeneous mixture among the three cases studied.