Change in Flame Geometry of an Ethanol Spray Flame by Varying the Spray Characteristics

Turbulent swirl flames using fuel sprays are found in many combustion systems. Since sprays with different characteristics can be produced, pulsed spray injection allows the realization of different flame types using the same burner. Two different flame types have been studied experimentally and numerically: a burner-attached and a lifted flame. Large eddy simulations using Lagrangian particles to represent the spray, and a combined presumed PDF and tabulated chemistry approach to model the turbulent combustion are able to represent the different flame types. A simple-to-implement improvement of the numerical algorithm for the droplets is proposed, consisting of the redistribution of the droplet source terms between all neighbor cells of the gas phase. This improvement stabilizes the numerical method and allows the use of large time steps. The numerical results have been used to investigate the phenomena leading to the different flame geometries. They show that the burner-attached flame is caused by a destructive interaction between the spray droplets and the central recirculation zone (CRZ). In the case of the lifted flame, the CRZ is preserved.