Spraylets-a Way to Simulate Spray Autoignition

Abstract

A new approach for spray ignition simulation is presented. Since the numerical effort of simulating an evolving　spray within a hot and pressurized ambient from shortly after inj ection until ignition is interminable, the problem　is tackled by splitting the simulation into two tasks. A CFD package is used to calculate a two phase flow through a simulation domain based on a configuration model. From this two phase flow droplet track data and gas phase values are extracted to serve as variable boundary conditions for the second task, the one dimensional single droplet ignition simulations, which are fully transient and based on detailed chemistry, named spraylet. The obtained ignition delay times can be transformed into spatial distributions of ignition probability. While the CFD part is handling spray formation, turbulence, temperature, pressure and global vaporization within the confinements, the spraylet calculations take care of droplet related physics and chemistry. The reworked model is able to reproduce single and multistage ignition and simulation can be performed beyond the limit of complete evaporation. The software framework for this approach has been implemented using a dummy function as substitute for the spraylet calculations still under development. The dummy function, which is intended for testing purpose only, comprises a very simple ignition criterion based on a threshold temperature.