Unsteady injection of sequences of drop clusters in vortices depicting portions of a spray

Abstract

A model of unsteady injection of sequences of drop clusters embedded in jet vortices was applied to describe both vortices in the shear layer of a spray and small-scale vortical structures in the core of a spray. In the first case, the vortices are large compared to the size of the spray, they rotate fast with respect to the injection rate, and their number per area of spray is small. In the second case, the vortices are small compared to the size of the spray, they rotate slowly with respect to the injection rate, and their number per area of spray is large. Results were obtained for injection sequences where either the drop size or the air/fuel mass ratio varied from cluster to cluster in the injection sequence. The variation was a mono-tonic increase, a monotonic decrease, or a sinusoidal variation. The results thus obtained were compared to baseline results from steady-state calculations. Additionally, both the entrainment from the ambient into the jet and the initial number of clusters per jet area were varied so as to ascertain their influence on cluster penetration and jet properties. The results show that penetration of a cluster into the ambient is a function of the characteristics of the cluster sequence following the cluster, that the jet temperature is controlled by entrainment from the ambient into the jet in the shear-layer application whereas conduction also becomes important in the spray-core application, and that the fuel mass fraction in the jet is a function of the initial characteristics of the clusters as well as entrainment.

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