Large eddy simulation of high gas density effects in fuel sprays

Abstract

The paper focuses on the physics of sprays using large eddy simulation (LES) and Lagrangian particle tracking (LPT). The LES/LPT was compared to previously unpublished experimental fuel spray data in two ambient gas densities, 39 and 115 kg/m3. The higher density case corresponds to a nearfuture engine environment with maximum cylinder pressure of the order of 300 bar, whereas the lower density case resembles typical present-day engine conditions. The accuracy of the results was quantified by calculating the resolved part of the turbulent kinetic energy and using a LES quality index analysis. The sprays produced by the LES/LPT had many similarities with the experimental sprays. On a global scale, spray penetration, spray opening angle, and spray dispersion were found to be well captured by the LES/LPT. The results indicated that the effect of subgrid scales on particle dispersion was small and hence no explicit particle dispersion model was required. Similarities were also found locally as LES/LPT produced small-scale flow structures indicated by the Q-criterion, preferential concentrations, and voids free of droplets. Finally, we propose a new gas phase mixing indicator in order to quantify turbulent mixing. Results from the novel mixing indicator suggest that for a given spray penetration, the higher ambient gas density spray yields an increased mixing rate. © 2013 by Begell House, Inc