CFD Modeling and Validation of the ECN Spray G Experiment under a Wide Range of Operating Conditions

The increasing diffusion of gasoline direct injection (GDI) engines requires a more detailed and reliable description of the phenomena occurring during the fuel injection process. As well known the thermal and fluid-dynamic conditions present in the combustion chamber greatly influence the air-fuel mixture process deriving from GDI injectors. GDI fuel sprays typically evolve in wide range of ambient pressure and temperatures depending on the engine load. In some particular injection conditions, when in-cylinder pressure is relatively low, flash evaporation might occur significantly affecting the fuel-air mixing process. In some other particular injection conditions spray impingement on the piston wall might occur, causing high unburned hydrocarbons and soot emissions, so currently representing one of the main drawbacks of GDI engines. Within this context, a deep understanding of the spray evolution by means of accurate experimental and numerical investigations is of great importance for reduction of pollutant emissions and fuel consumption. This work is focused on the CFD simulation of the 8-hole, ECN Spray G injector under constant volume conditions. Calculations were carried out with the LibICE code, which is based on the OpenFOAM technology. Different ambient pressure and temperature conditions were investigated for a comprehensive evaluation of the proposed numerical setup. The resulting developments of the jet plumes were assessed, along with the physical effects of injection pressure and sub-atmospheric ambient pressure conditions. The capability of the code in describing the spray evolution in terms of penetration and diffusion under flash-boiling conditions was here analyzed. A validation of atomization, secondary breakup and wall impingement models was performed through a comparison with experimental data obtained with optical techniques characterized by a hybrid Mie-scattering/schlieren approach. The spatial distribution and the time-resolved evolution of the free sprays were derived along with their post-impingement characteristics.