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An experimental investigation has been carried out of the turbulence characteristics of tumble air motion in four-valve pent roof combustion chambers. This was conducted on an optically accessed single cylinder research engine under motored conditions at an engine speed of 1500 rev/min. Four cylinder heads with varying tumble magnitude were evaluated using conventional and scanning Laser Doppler Anemometry (LDA) measurements. Analysis algorithms developed to account for the effects of mean flow cyclic variations and system noise were used to obtain unbiased estimates of turbulence intensity and integral length scales. The cylinder heads were also evaluated for combustion performance on a Ricardo single cylinder Hydra engine. Mixture and EGR loops at 1500 rev/min and 1.5 bar BMEP were carried out and cylinder pressure data was analysed to derive combustion characteristics.

A scanning Laser Doppler Anemometer system has been developed for the measurement of spatial velocity profiles in motored internal combustion engines. Tests were carried out on a single cylinder engine with a disc shaped combustion chamber, at an engine speed of 1200 rev/min. Ensemble averaged mean and RMS velocity estimates show good agreement with conventional LDA measurements. Longitudinal and transverse autocorrelation functions have been calculated, and estimates have been made of turbulence length scales. These have been found to be comparable with length scales measured in engines by other techniques. This investigation has demonstrated that scanning LDA is a powerful technique for characterising in-cylinder air motion in engines.

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.