A 1d Model for the Prediction of Flash Atomization in Gdi Multi-Hole Injectors: Preliminary Results 2008-01-2516
A flash evaporation model is being developed to capture the effects of bubble nucleation and growth inside multi-hole injector nozzles to investigate the flash evaporation in fuel injector sprays in Gasoline Direct Injection (GDI). The 1D flash evaporation model is a key tool for providing the 3D Eulerian-Eulerian or Lagrangian spray simulation model with the right droplet size in order to properly predict the effect of degree of superheating on mixture formation. Super heating conditions are likely to be found under partial load conditions in GDI applications or they might be deliberately induced to enhance fuel atomization and vaporization. A quasi-1D nozzle flow model has been developed to help quantifying the effects of main physical and geometrical parameters in promoting fuel flash evaporation. This model is based on an weakly compressible homogenous two-phase mixture assumption. A non-equilibrium model is used to predict the vapour formation rate along the nozzle. A fully explicit method based on a two-step Lax-Wendroff method is used together with a TVD scheme. An atomization model has been proposed to correlate the void fraction at nozzle exit to the most probable radius of the droplet generated from flashing atomization. An accurate two phase speed of sound is adopted allowing to predict the choked flow conditions once saturation has been reached. Metastable states are not considered in this first approach. A preliminary validation has been carried out based on an experimental nozzle flow configuration at two different values of superheating degree. A preliminary assessment of the model capability in capturing the effect of fuel conditions on droplet most probable diameter is presented.