Stroboscopic Laser Shadowgraph Study of the Effect of Swirl on Homogeneous Combustion in a Spark-Ignition Engine

A photographic study is presented illustrating the influence of mixture motion on flame propagation in an internal combustion engine. Variation in swirl and turbulence levels was achieved by rotating the orientation of a shroud on the intake valve. Laser Doppler velocimetry was used to characterize the precombustion fluid motion. A flexible shadowgraph system was developed for visualizing in-cylinder events. The results show that cyclic variation is not necessarily decreased by increasing the burn rate. The fastest burn achieved in this study occurred with high swirl, when the flame remained attached to the spark plug. If random detachment of the flame occurred, however, cyclic variation was greatly enhanced.