Nozzle Flow and Spray Development One-Way Coupling Methodology for a Multi-Hole GDi Injector

The use of predictive models in the study of Internal Combustion Engines (ICE) allows reducing developing cost and times. However, those models are challenging due to the complex and multi-phase phenomena occurring in the combustion chamber, but also because of the different spatial and temporal scales in different components of the injection systems. This work presents a methodology to accurately simulate the spray by Discrete Droplet Models (DDM) without experimentally measuring the injector mass flow rate and/or momentum flux. Transient nozzle flow simulations are used instead to define the injection conditions of the spray model. The methodology is applied to a multi-hole Gasoline Direct injection (GDi) injector. Firstly, the DDM constant values are calibrated comparing simulation results to Diffused Back-light Illumination (DBI) experimental technique results. Secondly, transient nozzle flow simulations are carried out. The computational values of mass flow rate and momentum flux (therefore, the discharge and velocity coefficients) of the nozzle are obtained. Afterwards, they are used as an input for the spray DDM calculations. These computational spray results are again compared against the experimental data, showing that the liquid spray penetration into the combustion chamber is accurately predicted for a wide range of injection conditions in terms of injection pressure and ambient back density. It is also shown how the opening transient slope of the rate of injection plays a major role in predicting the early evolution of the spray, the first 10 mm of penetration.