Cavitation Initiation, Its Development and Link with Flow Turbulence in Diesel Injector Nozzles 2002-01-0214

The initiation and development of cavitation in enlarged transparent acrylic models of six-hole nozzles for direct injection Diesel engines has been visualised by a high-speed digital video camera in a purpose-built refractive index matching test rig. The obtained high temporal resolution images have allowed improved understanding of the origin of the cavitation structures in Diesel injector nozzles and clarification of the effect of sac geometry (conical mini-sac vs. VCO) on cavitation initiation and development in the nozzle holes. The link between cavitation and flow turbulence in the sac volume and, more importantly, in the injection holes has been quantified through measurements of the flow by laser Doppler velocimetry (LDV) at a number of planes as a function of the Reynolds and cavitation numbers. The anticipated enhancement of turbulence through the onset of cavitation was identified only at the entrance to the injection holes, with its effect most pronounced on the size of the developing cavitation bubbles and the homogeneity of the two-phase flow mixture at the nozzle hole exit.