Validation of Diesel Fuel Spray and Mixture Formation from Nozzle Internal Flow Calculation

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. The transient data of spatial distributions of velocity, turbulent kinetic energy, dissipation rate, void fraction rate, etc. at the nozzle exit were extracted. These output data were transferred to the spray calculation, in which a primary break-up model was applied to the Discrete Droplet Model (DDM). The calculation results were compared with the results of the measurement data of spray in a constant volume vessel, and the engine in-cylinder visualization results of high speed and full load operating condition. Predicted spray shape, Sauter mean diameter, penetration, and fuel mixture shape showed good agreement with the experimental data.