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The paper describes a 1D-3D modeling technique for the simulation of the fuel injection systems. The technique is based on the one-dimensional modeling of the fuel flow and the mechanical motion of the injection system with the AVL software HYDSIM (from e.g. the fuel rail up to the nozzle chamber) and three-dimensional modeling of the nozzle flow with AVL-FIRE (from the needle seat through the spray holes up to the combustion chamber). The nozzle mesh, including the nozzle sac region with spray holes and (optionally) the lower part of the nozzle chamber, is created with the FIRE Preprocessor. The interface between the 1D and the 3D simulation regions can be freely chosen within the nozzle chamber at any position between the needle seat and guide.

A series calculation methodology from the injector nozzle internal flow to the in-cylinder fuel spray and mixture formation in a diesel engine was developed. The present method was applied to a valve covered orifice (VCO) nozzle with the recent common rail injector system. The nozzle internal flow calculation using an Eulerian three-fluid model and a cavitation model was performed. The needle valve movement during the injection period was taken into account in this calculation. Inside the nozzle hole, cavitation appears at the nozzle hole inlet edge, and the cavitation region separates into two regions due to a secondary flow in the cross section, and it is distributed to the nozzle exit. Unsteady change of the secondary flow caused by needle movement affects the cavitation distribution in the nozzle hole, and the spread angle of the velocity vector at the nozzle exit.