Experimental Investigation of the Internal Flow Field of a Model Gasoline Injector Using Micro-Particle Image Velocimetry

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. We have measured between conditions corresponding to approximately engine idle (Reynolds and Cavitation numbers of Re = 4600 and C = 6850 respectively, based on a reference plane upstream of the needle valve centring boss) to just after the onset of cavitation at the nozzle plate (Re = 10700 and C = 2700). It was found that the mean flow field was Reynolds number dependent and that, downstream of the needle valve guide boss as well as upstream of the nozzles, the mean flow consisted of complex, strongly three dimensional flow patterns. Increased levels of turbulence kinetic energy, relative to the sections upstream, were measured near the exit nozzles close to the area where cavitation occurred. Inviscid estimates of static pressure, based on PIV data, showed that the flow between the needle valve and its seat was also close to cavitating conditions at this needle valve lift for Re = 10700.