Flow Simulation With Needle Movement of Diesel Nozzles With Alternating Diameter

As the reduction of the nozzle hole diameter in diesel injectorsleads to a better vaporization and mixture generation, thenozzle geometry is considered as a key factor to face stricteremission standards. Many researches have been conductedconcerning the inner nozzle flow and especially the cavitationformation in the nozzles. In these studies, the geometricalinfluence of the nozzle shape on flow development is analyzednumerically. To reduce simulation time, sector models are used.One nozzle is simulated separately and the flow in the sac holeis assumed to follow symmetric boundaries. In this work, a newdesign of diesel nozzle is presented using 12 spray holes withalternating diameters (6 big and 6 small nozzles). The goal is toenhance air utilization during the combustion process byincreasing the spray covered volume in the piston bowl. Withthis design symmetric boundaries can only be set by simulatingtwo nozzles simultaneously. To analyze the influence of usingalternating nozzle hole diameters in one model severalsimulation are conducted. Three nozzle designs with 8, 12 and6+6 holes are examined and three types of models simulatingup to 6 nozzles simultaneously are applied. All nozzles have thesame hydraulic flow rate. In transient simulations the innerflow of these nozzles is analyzed, including the needlemovement. Compared to a sector model of an 8-hole nozzle,the flow field shows differences using alternating diameters ofspray holes at various needle positions. Since the flow field atthe nozzle outlet can be used as initial conditions forcontinuative spray simulations this effect may influence thespray angle and spray penetration.