Novel methods for 3D-CFD simulation of flash-boiling and multi-component fuel sprays

The development of the Gasoline Direct Injection technology for current and future energy landscapes requires advanced knowledge on the influence of fuel properties on the combustion process. For this purpose, modern numerical methods, such as Computational Fluid Dynamics simulations(CFD), are applied. This thesis has for objectives to investigate two fuel-related phenomena in 3D-CFD computations, which are the flash-boiling effect and the evaporation of multi-component fuel sprays. An experimental analysis of the phenomenon of flash-boiling is first carried out in a pressure chamber. A computational analysis of the flash-boiling effect is then performed by means of spray simulations in the pressure chamber. A novel model called Superheated Breakup Model is presented, which predicts the breakup of superheated droplets. A novel method called DC-Omega (Discrete Composition function of evaporated fraction Omega) for the computation of multi-component droplet evaporation is presented. In this approach, the evolution of composition in a multi-component droplet is predicted ahead of CFD-simulation by means of a series of phase equilibrium computations. The DC-Omega method is validated on the basis of simulations of atmospheric distillation, as well as simulations of two experiments of the literature on the evaporation of pure and multi-component single drops. The DC-Omega method is applied in order to investigate the mixture formation of multicomponent fuels in an optically-accessed engine. The analysis of the gaseous phase confirms initially assumed temporal and spatial fluctuations of fuel composition. A study of computational cost confirms the simultaneous effectiveness and accuracy of the applied method.