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A full-field, time-resolved interferometric method for the characterization of sparse, polydisperse spray systems is reported. The method makes use of the angular intensity oscillations in the wide-angle forward-scatter region. A pulsed laser is used to illuminate a planar sheet through the spray, which is imaged, out of focus, from the 45°direction. The image consists of a set of out-of-focus spots, each of which represents an individual droplet, and superimposed on which is a set of fringes corresponding to the angular intensity oscillations of that droplet. Macrophotographic recording with high-resolution digitization for image analysis provides a full-field capability. The spatial frequency of fringes on each spot in the image plane is dependent on the diameter of the corresponding droplet in the object plane, and a simple geometric analysis is shown to be appropriate for the calculation of the spatial frequency of fringes as a function of droplet size. Images are analyzed automatically by a software suite that uses Gaussian blur, Canny edge detection, and Hough transforms to locate individual droplets in the image field. Fringe spatial frequency is then determined by least-squares fitting to a Chirp function. The method is applicable to droplets with diameters in the range of several millimeters to several hundred millimeters and number densities of up to 10(3) to 10(4). The accuracy of the method for droplet-size determination has been evaluated by measurements of monodisperse aerosols of known droplet size, and measurements of droplet-size distribution in a polydisperse aerosol produced by a gasoline fuel injector are also presented. An extension of the method, using high-speed photography to measure two components of velocity in addition to size and position, is discussed. A two-wavelength approach may also offer the capability to measure the concentration of model fuel additives in droplets, and the results of a feasibility study are described.

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This paper describes an inuestigation into the effects of in-cylinder air motion at the spark plugs on gasoline engine performance. Measurements of combustion angles have been made in a single-cylinder four-stroke disc combustion chamber engine at part load and MBT ignition timing. Seventeen in-cylinder air motion regimes have been produced using masked valves. The air motion in each build has been evaluated by making laser Doppler anemometry (LDA) measurements of mean velocity and turbulence intensity at the spark plug position under motored conditions. It has been shown that there is a strong correlation between turbulence intensity and 10-90 per cent burn angle. I t is demonstrated that for this combustion chamber geometry a tumbling air motion is a more effective means of generating turbulence at TDC than swirl.Do0389

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