Experimental Investigation of the Sprays of an Axi-Symmetric Nozzle of a Common-Rail High Pressure Electro-Injector

An axi-symmetric, five-hole V.C.O. nozzle mounted on an electro-injector was used to analyze the spray produced by each hole varying feeding pressure, injected quantity and timing. An advanced experimental apparatus has been used to investigate particle size and velocity of the sprays. The investigation comprized a hydraulic characterization, a photographic one with back-light technique, the analysis of the droplet size distribution through laser diffraction technique via MALVERN 2600 SERIES and the analysis of particle size and velocity using PDPA technique (AERMETRICS DSA 4000) with the extremely dense spray produced by the common-rail electronically controlled injection system. Four feeding pressures (25, 30, 90, 120 MPa) and five injected quantities (2, 4, 10, 25, 40 mm³/shot) were chosen to characterize the nozzle behavior.

Sprays from different holes appeared different in shape but very similar in the droplet size distribution. Each spray had a dense internal core with low SMD and a periphery with a higher one. PDPA techiques showed severe limitations in the investigation of a so highly dense spray and for this reason a feeding pressure of 15 MPa was chosen after having reduced the probe volume with a spatial filter of 50 μm and having increased the laser power up to 5 W.