An Investigation into Turbulence in Engines using Scanning LDA

An investigation has been carried out to compare the ability of swirling and tumbling flow regimes to enhance the turbulence in a disc-shaped gasoline combustion chamber. Scanning LDA measurements have been made of spatial velocity fluctuations in a high swirl, a tumble and a baseline low swirl build. All of the testwork was carried out under motored conditions at an engine speed of 1200 rev/min.

A parametric model has been developed to account for the effects of mean flow cyclic variation and system noise. It is shown that the model fits very well to the experimental data, enabling unbiased estimates of turbulence intensity and turbulence length scale to be made.

In the region measured around TDC the high swirl build achieves a uniform increase in turbulence Intensity of about 55% over the baseline build. The tumble build however achieves a peak in turbulence intensity of more than twice the baseline build at 30° BTDC. Turbulence length scales are similar for the high swirl and baseline builds, and about 30% larger for the tumble build.