Fluid Motion during Flame Propagation in a Spark Ignition Engine

Laser Doppler velocimeter results are presented for the mean velocity and turbulence intensity measured during combustion in a research engine. Simultaneously with each LDV measurement, the cylinder pressure and gas state (unburned or burned) were measured so that conditional sampling techniques could be used in the data-averaging procedure.

Measurements of the mean velocity component in the direction of flame propagation agree well with a computer simulation of the induced velocities generated by the volume expansion of the burned gases. Mean velocities measured parallel to the flame surface are shown to be complex because a small amount of swirl was present. Conditional sampling on the time of flame arrival at the LDV probe volume revealed a thirty percent cyclic-variation bias error in the turbulence component normal to the flame. The turbulence field ahead of the flame appears to be enhanced by compression, with the component normal to the flame increased twice as much as the parallel component.