Multidimensional Modeling of Transient Gas Jet Injection Using Coarse Computational Grids

In spite of the efficiency of Computational Fluid Dynamics (CFD) as a design tool, numerical simulations of gaseous fuel injection have not been widely adopted because of the difficulty in modeling the complicated physical phenomena associated with high speed gas flows. In the present study, a new model for simulating transient direct injection of gaseous phase fuel, including hydrogen, into a combustion chamber using a practical computational grid was developed. The model was implemented into KIVA3V, a multi-dimensional CFD code. The new model employs several sub-models to describe the physical phenomena of high speed gas injection. The underexpanded jet issuing from the nozzle was modeled using the conditions at the Mach disk as inflow boundary conditions. The effect of turbulence is shown to lead to non-unique flow solutions. However, physically realistic flows are obtained by a new turbulence treatment that describes the turbulence length scale and turbulent kinetic energy near the gas jet exit. The model considers time-varying pressure downstream of the injection nozzle by using a hybrid combination of a theoretical jet model and the underexpanded jet model. The model was applied to simulate a single-hole nozzle gas jet injection into a constant volume chamber and the results are compared with the classical jet theory and available literature data. Excellent agreement was attained between the predictions and the theoretical and experimental penetration profiles of gas jets. Compared to the results calculated using a fine mesh, the model successfully predicts gas jet behavior with a coarse grid and thus saves computation time, and can be used in practical device simulations.