Experimental study of cavitating flow inside vertical multi-hole nozzles with different length-diameter ratios using diesel and biodiesel

The complicated cavitating flow inside diesel nozzles has long been concentrated on, and cavitating flow characteristics of biodiesel in nozzles with different structures is instructive to the highly efficient use of biodiesel in diesel engines. In this paper, on the visualization experimental system with a transparent scaled-up injector nozzle tip and the high-speed digital camera were used to investigate the cavitating flow in transparent VCO nozzles with different length-diameter ratios (L/D) using diesel and biodiesel, and the energy loss in the occurrence of the hydraulic flip was also analyzed. Moreover, the nozzle cavitating flow characteristics were studied not only during the period of increasing of injection pressure but also decreasing of injection pressure. The hydraulic flip phenomenon occurred in nozzles with L/D of 4 and 6, but not appeared in nozzles with L/D of 8. The cavitation is easier to occur for the diesel than for the biodiesel. The nozzle discharge coefficient for the diesel is higher than that for the biodiesel when the flow is single-phase turbulent flow, while it got much smaller for the diesel than that for the biodiesel when the cavitating flow and the hydraulic flip phenomenon occur. The critical number of cavitation inception is smaller than that of cavitation disappearance.