1996-02-01

A Computational Investigation of the Spray-Induced Flow and its Influence on the Fuel Distribution for Continuous and Intermittent DI-Diesel Sprays 960631

The underlying computations examine the spray mean flow and its influence on the fuel distribution under non-reacting conditions, with a particular focus on the application to intermittent, equally-pulsed DI-Diesel sprays. The fuel is injected from the top center of a cylinder in axial direction into quiescent air of 800 K and 120 bar. The fuel flow rates are controlled with the nozzle diameter, keeping the injection pressure constant. The computations have been performed with a KIVA-3 based code on a CRAY-YMP.
The spray-induced gas flow interacts with the fuel droplets which leads to an increased collision activity at the tip of the spray and near the nozzle exit, and, via coalescences, results in the formation of larger lumps of fluid. The effect of this droplet clustering has been investigated for various fuel flow rates of continuous and intermittent DI-Diesel sprays. Particular attention has been given to the temporal behavior of the evaporation, the spray penetration, and the evolution of scalar fields for various gas quantities. It is observed that the lump formation becomes more intense with increasing nozzle diameter and counteracts the initially well-developed spray atomization, thus yielding poor evaporation but increased penetration.
For intermittent, short-pulsed sprays with large fuel flow rates, the droplet clustering leads to the formation of liquid lumps of fuel which dominate the evolution of the spray. Further, the previously described accumulation effect is observed again, but between liquid fuel blobs of subsequent pulses.
Finally, in order to estimate the extent of the lump formation, a series of computations with the collision model switched off is compared with the standard data.

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