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This research demonstrates the capability of the Laser Doppler Anemometer (LDA) for making measurements inside a piston-engine cylinder. The backscatter mode of LDA operation, requiring only a single window in the cylinder, was used. An ensemble-average data-processing technique has been developed to analyze the raw velocity-crankangle data. Single-component measurements of mean velocity and rms velocity fluctuation at a single point are presented as functions of crankangle for three engine speeds. A comparison of motored and fired results is shown for one engine speed. Measurements of two components of velocity at several locations show the basic vortical nature of the flow field in this particular engine.

Air velocities at several points near the spark plug location were measured using a laser Doppler anemometer (LDA) in a motoring internal combustion engine. This engine was equipped with three intake configurations: a standard valve in a standard port, a standard valve in a helical (swirl) port, and a shrouded valve in a standard port. Both ensemble-averaged and cycle-resolved mean velocities were determined; this allows comparison of rms velocity fluctuation, cycle-resolved turbulence, and cycle-by-cycle variations in mean velocity. Frequency domain analysis of these components was also carried out. The main conclusion of this experimental study was that starting from a very low swirl situation (standard valve case), addition of a moderate amount of swirl (swirl port case) goes a long way towards improving cycle repeatability and increasing cycle-resolved turbulence. Increasing swirl even further (shrouded valve case) does not produce further dramatic improvements.