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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.

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.

Measurements are presented of droplet characteristics and air velocity in the cylinder of a 0.36 litre four valve engine, equipped with an sohc VTEC-E valve train and port injection. The results show that injection at crank angles, θinj(s), when the inlet valve is open results in most of the liquid volume flux being in the form of droplets with Sauter mean diameter between 20 and 30 mm which strikes the sleeve up to about 2.5 cm below the exhaust valves, thus generating a locally rich cloud there. The amount of liquid phase gasoline passing through the plane 16 mm below the spark plug gap increases with θinj(s) up to 50 CA after intake TDC and this, together with the crank angle of droplet arrival and vapour generation, controls stratification of the gaseous fuel phase. The optimum injection time is when the fuel-rich cloud is generated so that the tumble vortex convects it to the spark plug at the time of ignition.