Numerical Simulation of Diesel Sprays Using an Eulerian-Lagrangian Spray and Atomization (ELSA) Model Coupled with Nozzle Flow

High-pressure diesel sprays were simulated with an Eulerian-Lagrangian Spray and Atomization (ELSA) model, based on a multidimensional engine computational fluid dynamics (CFD) code KIVA-3V. The atomization of the dense liquid core in the near-nozzle region was modeled with turbulent mixing of the diesel fuel with the ambient gas. Under the continuum assumption of a fuel-air mixture in this region, two transport equations were solved for the liquid mass fraction and liquid surface area density. At a certain downstream location where the spray became dilute, a switch from the Eulerian to the Lagrangian approach was made to benefit from the advantages of the conventional Lagrangian droplet models, such as droplet collision and turbulent dispersion modeling. The droplet size and velocity to be initialized at this switch were determined by the local CFD cell properties. As an integral part of this study, the internal nozzle flow of a 7 hole, midi sac injector was simulated with a Homogeneous Equilibrium Model (HEM). The model assumed an isothermal mixture of fuel liquid and vapor, whose pressure and density can be related by the speed of sound. The results at the nozzle exit were coupled with the ELSA spray simulation by an interpolation procedure to provide realistic inflow boundary conditions. This entire methodology was validated by considering liquid spray penetration and droplet size distributions under non-evaporating chamber conditions. Good agreement was found with the available data, indicating the model's capability as a numerical tool to study diesel spray atomization.