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ICLASS 94<br>Proceedings of the Sixth International Conference on Liquid Atomization and Spray Systems

ISBN:
978-1-56700-019-1 (Print)
978-1-56700-445-5 (Online)

UNSTEADY INJECTION OF SEQUENCES OF DROP CLUSTERS IN VORTICES DEPICTING PORTIONS OF A SPRAY

Josette Bellan
Department of Mechanical and Civil Engineering, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

K. Harstad
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

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. 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 either a monotonic increase, or a monotonic decrease, or a sinusoidal variation. These results were compared to those from steady-state calculations. 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 upon cluster penetration and jet properties.

Penetration of a cluster into the ambient is controlled by the characteristics of the cluster sequence; the jet temperature is controlled by entrainment from the ambient into the jet in the shear layer application whereas conduction becomes also important in the spray core application. The fuel mass fraction in the jet is a function of the initial characteristics of the clusters as well as entrainment. It is concluded that experimental observations should be interpreted with caution because they are usually performed in an Eulerian frame, whereas Lagrangian modeling is required in order to correctly interpret some of these observations.