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Spray characteristics of injectors depend on, among other factors, not only the level of turbulence upstream of the nozzle plate, but also on whether cavitation arises. "Bulk" cavitation, by which we mean cavitation which arises far from walls and thus far from streamline curvature associated with salient points on a wall, has not been investigated thoroughly experimentally and moreover it is quite challenging to predict by means of computational fluid dynamics. Information about the effect of the injector geometry on the formation of bulk cavitation and quantitative measurements of the flow field that promotes this phenomenon in gasoline injectors does not exist and this forms the background to this work. Evolution of bulk cavitation was visualized in two gasoline multi-hole injectors by means of a fast camera.

Controlling the spray characteristics of a Diesel injector means understanding the internal flow field and the way that cavitation is initiated. Measurements of the internal flow field of an injector are rare, although they provide the appropriate information both on the flow pattern and the initiation of cavitation in order to assist the evaluation of computer predictions of flow and cavitation. The purpose of the current work is to report measurements of the internal flow of a Diesel injector and assess the ability of computational fluid dynamics to predict the flow behaviour. Two-Dimensional Particle Imaging Velocimetry (PIV) technique was employed to measure the internal flow field of a Diesel injector. The experiments were conducted by using 20:1 scale transparent models of different sections upstream of the injection nozzle of a commercial Diesel Injector.

The spray characteristics of a gasoline injector depend not only on the physics of atomization of the liquid jet on exit from the nozzle plate but also on the level of turbulence generated by the internal flow, upstream of the nozzle plate, as well as on whether cavitation arises. Measurement of the internal flow field of an injector can thus provide useful information and can assist the evaluation of the accuracy of computer predictions of the flow and associated cavitation. Information about the flow field upstream of nozzle exits is, however, rare and this forms the background to this work. Two-Dimensional Micro Particle Imaging Velocimetry (μPIV) was employed to measure the internal flow field in planes parallel to a plane of symmetry of the injector, downstream of the needle valve centring boss of a 10:1 super-scale transparent model of an 8-nozzle gasoline injector, with exit model-nozzle diameters of 2mm and a fixed model-needle lift of 0.8mm.