Prediction of Liquid and Vapor Penetration of High Pressure Diesel Sprays

A dense-particle Eulerian-Lagrangian stochastic methodology, able to resolve the dense spray formed at the nozzle exit has been applied to the simulation of evaporating diesel sprays. Local grid refinement at the area where the spray evolves allows use of cells having sizes from 0.6 down to 0.075mm. Mass, momentum and energy source terms between the two phases are spatially distributed to cells found within a distance from the droplet centre; this has allowed for grid-independent interaction between the Eulerian and the Lagrangian phases to be reached. Additionally, various models simulating the physical processes taking place during the development of sprays are considered. The cavitating nozzle flow is used to estimate the injection velocity of the liquid while its effect on the spray formation is considered through an atomisation model predicting the initial droplet size. Various vaporisation models have been tested, including high-pressure and non-equilibrium effects and chemical composition change. Different droplet break-up and droplet aerodynamic drag models are used to assess the predicted results. In particular, the increased surface area of the droplets associated with their fragmentation process is found to play a major role on the exchange of heat and mass between the evaporating liquid and the surrounding air. This has allowed for calculation of liquid penetration length independent of the injection pressure. The model has been successfully validated against experimental data for the liquid and vapour penetration under a variety of injection pressure, back pressure and temperature, injection hole diameter and fuel initial temperature and composition.