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Ionization probes installed in the head gasket of an engine have been used to infer the shape of the burned volume from measurements of when the flame contacts the gasket. It is demonstrated that the technique can be extended to infer fluid motion by using one of the ionization probes as the ignition site, with the ensuing flame serving as a flow marker. It is shown that swirl motion, and its direction, can be detected, and that flame propagation velocities can be measured. A comparison of estimated swirl velocities with laser Doppler velocimeter measurements show remarkably good agreement. The most valuable feature of the technique is that it can be applied to any production engine without modification.

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.