LES Based Modeling and Simulation of Spray Dynamics including Gasoline Direct Injection (GDI) Processes using KIVA-4 Code

In the GDI engines, the accuracy of the numerical results and their contribution to the design analysis and optimization tasks strongly depend on the predictive capabilities of the physical processes. While most of the studies apply RANS concept, in this contribution LES methodology is suggested as suitable unsteady approach for simulating spray dynamics including GDI processes using KIVA-4 CFD-code. A comprehensive model is integrated in a Eulerian-Lagrangian framework allowing to describe the spray evolving from the injector nozzle and propagating within the combustion chamber. It includes sub-models to account for various relevant sub-processes. The atomization is described using combined primary and secondary atomization sub-models. Instead of performing costly level set method or VOF technique, a LISA-based sub-model is applied for the primary atomization. The secondary atomization is modeled by a TAB model. The novelty of the proposed methodology is to include droplet-droplet interaction processes via an appropriate collision sub-model that is independent of mesh size and type. Thereby, it takes into account different regimes, such as, bouncing, separation, stretching separation, reflective separation and droplet coalescence. A resulting droplet distribution is then tracked in Lagrangian way. The droplet evaporation is described by an appropriate evaporation model and the turbulent dispersion by the filtered velocity only. The spray module is coupled to LES of the carrier phase in which a Smagorinsky model is used for the filtered flow field. The SGS scalar flux in scalar transport equations (of mass fraction and temperature) is captured by a simple gradient assumption. Comparisons of the simulation results in terms of spray profile with experiments for different injection times demonstrate that the essential features of the spray dynamics are reproduced to a good accuracy.