Numerical Investigation of Two-Phase Flow Evolution of In- and Near-Nozzle Regions of a Gasoline Direct Injection Engine During Needle Transients

This work involves modeling internal and near-nozzle flows of a gasoline direct injection (GDI) nozzle. The Engine Combustion Network (ECN) Spray G condition has been considered for these simulations using the nominal geometry of the Spray G injector. First, best practices for numerical simulation of the two-phase flow evolution inside and the near-nozzle regions of the Spray G injector are presented for the peak needle lift. The mass flow rate prediction for peak needle lift was in reasonable agreement with experimental data available in the ECN database. Liquid plume targeting angle and liquid penetration estimates showed promising agreement with experimental observations. The capability to assess the influence of different thermodynamic conditions on the two-phase flow nature was established by predicting non-flashing and flashing phenomena. Mild vapor formation inside the holes of the injector was predicted for flashing and non-flashing conditions, which suggests that there was sufficient depressurization of liquid fuel in a GDI nozzle. Outlet domain size and alignment of spray plumes with a grid were observed to be critically important to avoid numerical errors. Finally, to represent the real-world scenario of a moving needle in a GDI nozzle, simulations were carried out at different fixed needle lifts to provide insight to flow development inside a GDI nozzle, from opening to closing of the needle. Predictions indicated that flow patterns, and thus vapor formation characteristics, are considerably affected at very low needle lifts, for both flashing and non-flashing scenarios.