Experimental Investigation of Cavitation in Gasoline Injectors

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. Two-Dimensional Micro Particle Imaging Velocimetry (μPIV) was employed to measure the internal flow field of the injectors, just upstream of the exit holes of the injector plates at non-cavitating conditions and at conditions just after the onset of cavitation (for Type A model at a Reynolds Number of 10700 and a Cavitation Number of 2700, and for Type C model at a Reynolds Number of 9200 and a Cavitation Number of 6400). For the visualization and the measurements 10:1 we used super-scale transparent models of multi-hole gasoline injector plates, for Port Fuel Injection (PFI) application, with exit model-nozzle diameters of 2 mm and a fixed model-needle lift of 0.8 mm. Bulk cavitation was present in the models. PIV measurements of both types of injectors showed the presence of three-dimensional flow in the upstream nozzle plenum which may be related to the generation of a velocity field downstream, near the nozzles, which gives rise to bulk cavitation.