Preliminary LASER Doppler Anemometry (LDA) measurements of in-cylinder air motion in a motored optical engine are described and analysed. Emphasis is placed on the results obtained from the intake and compression strokes. Air velocities were measured close to top dead centre, where the interaction of air and fuel, when injected late in the compression stroke, realises a stratified charge. In the intake stroke, turbulence level is intense and unstructured. Compression stroke velocities are characterised by a lower level of turbulence, and hence subjected to easier approximation. Normal, Poisson and Gamma distributions are applied in order to approximate to the experimental data. Two different methods of statistical analysis (least square method and maximum likelihood estimation method) are used in order to provide the best possible fit to experimental data. The normal distribution is shown to give the most accurate approximation to the air velocity distribution for both intake and compression strokes. The results of LDA measurements are used to validate the predictions of the CFD package VECTIS of Ricardo Consulting Engineers.
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