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Laser Doppler Velocimetry (LDV) was used to make measurements of velocities and turbulence intensities at a location near the wedge-type combustion chamber center in a production SI engine under motored and firing conditions. The ensemble-averaged and conditionally-sampled data-processing techniques were employed to investigate the raw velocity data for motored and firing conditions respectively. The turbulence field measured under firing conditions is different from the motored data only after the spark ignition begins. There exists a dramatic change in ensemble-averaged mean velocity in the direction of flame propagation due to the fast volume expansion of burned gas when the flame front pass through the measurement point. Initially, the flame moves away from the spark plug and toward the measurement point, pushing the unburned gas ahead of it. Passage of the flame induces a horizontal velocity in the opposite direction.

The magnitudes and compositions of in-cylinder tumble ratio generated by each velocity components were computed at different intake valve lifts and distances along the direction of valve axis in this paper, based on the three-dimensional velocity data measured by hot-wire anemometry at intake valve periphery of typical SI engine intake ports (horizontal and sloping directed ports) in a steady flow rig. The effect of velocity profiles at above two intake ports exit on in-cylinder tumble generation was studied, and a microscopic analytical method of evaluating tumble-generating capability of intake ports was developed according to the velocity profiles at intake valve exit area.