Studies of the Effect of Spray Inlet Conditions on the Flow and Flame Structures of Ethanol-Spray Combustion by Large-Eddy Simulation

Abstract

Large-eddy simulation (LES) of ethanol spray-air combustion with a poly-dispersed initial droplet size distribution is presented here by using an Eulerian-Lagrangian approach, a sub-grid-scale kinetic energy stress model, and a filtered finite-rate combustion model with a sub-grid scale reaction rate called the second-order moment (SOM) combustion model, proposed by our research group. The simulation results are validated in detail by experiments. Furthermore, the flow and flame structures of spray combustion with different spray cone angles and cone angle thickness are studied. The results show that for the case of smaller spray cone angle thickness, the coherent structures in the high temperature zone tend to shed more clearly. High temperature develops around the coherent structures in the region of high vapor concentration, but not inside the large vortices. For the spray combustion with larger spray cone angle thickness, the vortex shedding at the outside of the flame zone is faster than that with smaller spray cone angle thickness. The instantaneous temperature maps of different spray flame structures with smaller cone angle thickness indicate the existence of small flame islands, expressing the droplet-group combustion, which is not observed in single-phase jet combustion and not obvious in the case of larger cone angle thickness.

Acknowledgments

This study was sponsored by the Project of National Natural Science Foundation of China under the grant 50736006, and by the State Key Laboratory of Engines, Tianjin University under the grant K2010-07.