Cfd analysis of a spray flame in a piloted diluted spray burner
A computational fluid dynamics simulation is developed for a spray flame of ethanol in a piloted diluted spray burner by using the commercial CFD code CFX 14.5. The goal is to obtain a better understanding of the uncertainty factors in spray combustion, like droplet evaporation, dispersion, the influence on the gas-air mixture, mixing and combustion. This can be a challenging task, since the physical phenomena involved in spray combustion are all interacting.
Experiments on a research burner performed at the University of Sydney are used to set-up and validate the numerical model of a stabilized spray flame. The research is restricted to the dilute spray regime by placing the nebulizer, which atomizes the liquid fuel into a spray, farther upstream than the jet exit plane. Initial breakup of the liquid spray is not considered and since part of the liquid droplets is already evaporated in the nozzle, a dilute spray is obtained at the jet exit plane.
The liquid fuel droplets are modelled as discrete particles in a continuous phase of gas-air mixture to observe the individual droplet behaviour. The global behaviour of the spray burner is correctly captured by the simulations, but in more detail some discrepancies are observed. The investigation focuses on the limitations of the numerical model and how they influence the results for both an open flame and a confined flame. The main issues encountered in the proposed model involve the inaccuracy of the sub-models of evaporation, turbulence and combustion, caused by their extent of simplification. Suggestions to improve the current model are made to develop a more sophisticated spray combustion model in the future.