Flame stabilization in many practical devices is achieved primarily through swirl; however, the application of swirl to an inverse diffusion flame and its effect on both flame stability and structure have not yet been reported. Therefore in this work, flame stability and structure of inverse diffusion swirling flames are investigated. The most stable flame is achievable at a critical swirl intensity, Scr. Lifted swirl jet-like flames at swirl intensity Scr are observed. Simultaneous PIV/OH-PLIF measurements are conducted to investigate the flame-flow interaction for three flames. The flame at Scr is stabilized due to the mutual dependence of two flame zones, the conical flame, and the flame root. The conical flame zone is located along with the inner shear layer (ISL) between the internal recirculation zone and the jet flow, while the flame root is positioned close to the burner nozzle. The ISL is favorable for flame stabilization due to the enhancement of the mixing of burned gas and fresh-fuel/air associated with the frequently-formed vortices. The flame root is stabilized due to the instantaneous opposed flow between the hot burned gas and the fresh reactants. The flame root essentially requires the upstream flow of hot exhaust gases associated with the IRZ. It is inherently unstable at high swirl intensities due to the high strain rate coupled with the strong IRZ. At low swirl intensities, the flame root is extinguished by the high momentum of the central jet, and a lifted flame is anchored in low-velocity regions of the jet, with the flame adjusting axially and radially to meet this criterion. These results emphasize the crucial role of the flame root in stabilizing the flame and suggest that well-aimed modifications of the flow field to further enhance mixing in this region may increase the stability of lifted jet-like swirling flames.
|Original language||English (US)|
|Journal||Experimental Thermal and Fluid Science|
|State||Published - Nov 8 2019|