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Volume-of-fluid large-eddy-simulations (VOF-LES) and optical imaging results of the primary breakup of a pulsed planar-sheet liquid jet are presented and compared. The planar-sheet thickness pertains to the GDI outward-opening conical-sheet spray. The investigations include injection conditions of 0.5 and 1 MPa fuel pressure and 0.3 MPa ambient pressure. The objective of the study is to assess the predictive accuracy of the VOF-LES method for analysis of the Kelvin-Helmholtz (KH) instability and the primary breakup of a transient, pulsed, liquid sheet jet, through inclusion of the injector nozzle flow domain into the simulations. Thus, the simulations do not resort to prescription of the issuing liquid jet velocity boundary condition. The results show good qualitative and quantitative accuracy for prediction of the KH interface instability waves and the liquid-sheet breakup process for the conditions studied.

Experimental (optical imaging) and CFD investigations of the cavitating flow in a transparent large-scale model of a GDi outward-opening injector, with a swirler-type valve-group, has been performed. The objective is to elucidate the flow structure within the valve group and assess a Reynolds-Averaged Navier-Stokes (RANS) multi-fluid simulation method. The optical imaging data show evidence of cavitation inception in the valve-group swirler-channels-caused by the rapid flow acceleration-and multiple cavitations within the conical nozzle region. The comparison of simulations with data shows that the CFD method reproduces the fluid dynamics of the valve-group with good qualitative agreement with the imaging data (with respect to the cavitation inception and geometry) and excellent quantitative agreement of the valve-group pressure drop-flow rate characteristic.

A combined experimental and computational investigation of the break-up structure of conical sprays of the high-pressure outward-opening gasoline direct-injection (GDi) injectors has been carried out, with the objective to investigate its distinct “jet-string” spray break-up structure. The study probes the relationship of the spray breakup structure to the liquid-phase flow within the injector nozzle - especially at the nozzle exit - obtained through Computational Fluid Dynamic (CFD) simulations. The shadowgraphy imaging technique is utilized for investigation of the spray morphology, and its dependence on the fuel pressure and the injector nozzle design. The Volume-of-Fluid Large-Eddy-Simulation (VOF-LES) computational method for two-phase flow simulation is employed for analysis of the injector internal flow and its proximate ambient, for the identical injector valve-group geometry.