Flow Field Effects on Flame Kernel Formation in a Spark-Ignition Engine

The effects of mixture turbulence and mean flow velocity on flame kernel formation in a spark-ignition engine were investigated using a disc-shaped optically accessible side chamber.

Three-dimensional flow predictions and LDA measurements were performed to get a better understanding of the flow field in this combustion chamber. Thin wire electrodes were located at a peripheral and a central position introduced into the combustion chamber via the glass windows. High-speed schlieren films at 40 kHz were taken from two orthogonal directions to visualize in detail the formation and development of the flame kernel. The purpose was to gain a better understanding of the interaction of turbulence and flame during the first milliseconds after spark breakdown of a transistorized coil ignition system and a capacitor discharge ignition system.

This study shows that the flame kernel is changed by the turbulence at flame radii of O.5 to 1 mm depending on turbulence intensity. At flame radii of more than 10 mm a fully developed turbulent flame has been formed. The influence of turbulence on the turbulent burning velocity during the flame kernel formation is less than during the main combustion period.