Large-eddy simulations of diesel spray with a fine grid in a constant-volume vessel

Abstract

In this study, a numerical methodology is developed to simulate liquid fuel spray, break-up and evaporation under high-temperature high-pressure diesel-engine-like conditions. First, the influence of the number of parcels on liquid fuel spray is studied using the Lagrangian parcel approach in an extended KIVALES code (the large-eddy simulation version of the KIVA code). In this study, Eulerian–Lagrangian momentum coupling is considered, incorporating the turbulent dispersion velocity in the spray source term. The study shows that a small number of parcels (about 5000 parcels) cannot represent the overall liquid fuel and droplet distributions. Increasing the number of parcels can enhance the vapour penetration length, but 40,000 parcels can effectively simulate the fuel spray with a fine grid of about 6 × 106 in our study. Use of the fine grid means that more information about the small-scale eddy structures can be obtained, especially in the vicinity of the nozzle. In addition, accurate large-eddy simulations are also used to study the influence of the swirl velocity. Subgrid turbulent dispersion associated with the subgrid turbulent kinetic energy is also found to be influential. Three zero-equation subgrid-scale models, namely the Smagorinsky model, the dynamic Smagorinsky model and the wall-adapting local-eddy-viscosity model, are compared in the study. In addition, the effect of incorporating an algebraic subgrid kinetic energy model into these subgrid-scale models is investigated. It is concluded that the algebraic subgrid kinetic energy model should be used with any of the above zero-equation subgrid-scale models to improve the quantitative predictions, even when the fine grid is used.