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The droplet characteristics of the air-assisted gasoline injector was investigated. A Phase Doppler technique was used to measure droplet diameter and its velocity. The size-classes technique was employed and found to be the best way to understand what kind of droplet is existing in shear flow induced mushroom vortex at spray shell. The detail spray characteristics near nozzle was discussed and the double shell structure was found. The droplets of less than 20 μm can be entrained into mushroom vortex, while the larger of over 30 μm penetrates straight to downstream. The slip velocity and relative Reynolds number were used in data analysis in order to understand the momentum transfer occurrence region due to strong drag force. The spray animation was demonstrated with the ensembled / size-classified droplet, which was found to be the powerful tool to understand spray formation and dispersion process.

This paper reports on an experimental study of dispersion process of an air-assisted injected spray with a view of optimizing its characteristics. A phase Doppler anemometer was used to measure the injected spray characteristics under open air condition. Ensembled average mean diameters and their velocities of fuel droplets were calculated for repetitive injections. The ensembled average mean velocity showed reasonable agreement with the velocity obtained by visualization. At higher load conditions, the atomization was achieved at high speed air flow such that the mean diameter was reduced. From medium to full load conditions, the fuel droplets were distributed in a tube-like profile due the shape of the nozzle. The first group of droplets had high velocity and small mean diameter in contrast to the second group. Relative slip velocity was not so small even in the fine droplets within the air flow from the injector as can expected.