Large Eddy Simulation of evaporating kerosene and acetone sprays

Abstract

Large Eddy Simulation (LES) is applied to turbulent kerosene and acetone sprays and the effect of turbulence and temperature fluctuations on the structure of the sprays under cold and evaporating conditions is discussed. Two different fuels were selected; kerosene which has a relatively high boiling point (480 K) at atmospheric pressure, and acetone, which has a boiling point of 329 K and thus evaporates at room temperature. In both cases liquid fuel is injected into a co-flowing air stream, which in the kerosene case is preheated at 450 K. A Lagrangian formulation is adopted for the particle dispersion coupled with an Eulerian description for the continuous phase. The Ranz–Marshall correlations are used for the Nusselt and Sherwood numbers. A stochastic model has been used for the representation of the sub-grid scale velocity fluctuations on the particle motion and temperature. The results show good agreement when compared with the experimental findings. The mean velocities of the liquid phase are found to follow the behaviour of a conventional jet flow and the profiles of the rms fluctuations are characterised by local maxima and minima, that indicate the location of the shear layers. The spreading rate is inversely related to the droplet size; as the size of the dispersed phase increases, the spreading rate is reduced. The maximum liquid flux decreases with the downstream distance, due to the evaporation of the liquid phase. Smaller particles were found to be dragged in the core jet region and droplet evaporation, was shown to be a size-selective process, enhanced for smaller particles.