Simulation of Primary Breakup for Diesel Spray with Phase Transition

A continuum formalism for describing the behavior of primary atomization with phase transition is presented, which includes the effects of heat and mass transfer of the two phase flow, the formation of ligaments and droplets, surface tension force and turbulence. Simulation of liquid jet primary atomization given by Marcus Herrmann (A balanced force refined level–set grid method for two–phase flows on unstructured flow solver grids, Journal of Computational Physics 2008) is extended to include the effects of evaporation and its relative motion of the interface between gaseous and liquid phase. It is shown that the phase transition process can be modeled by introducing a laminar surface regression velocity, which is the eigenvalue of thermal equilibrium. It is shown that the phase transition effect has a big impact on the the spray primary breakup processes. Introduction Numerical simulation of diesel engine combustion has become an important tool in engine development. One major issue in the modeling of turbulent reactive flows is the turbulent spray that accompanies fuel injection. One way to model the injection process is to use level–set method to describe the physical details of spray breakup; especially, primary breakup, the very first fragmentation process when liquid column rushes out of a nozzle, forming ligaments and breaking up into primary droplets [2]. If liquid fuel is injected into the combustion chamber, the high ambient temperature will enhance the phase transition process(from liquid fuel to fuel vapor). Fig. 1 shows slow and fast evaporation processes, leading to totally different sprays: the upper injection by T = 293K, the lower case by T = 800K. In order to simulate diesel injection(characterized by strong evaporation), the level–set method has to include the phase transition effect. Figure 1: Spray liquid–phase penetration with different ambient temperatures In the following sections, firstly, the original level-set method is briefly described. Then, the phase ∗Corresponding author: [email protected]