Flow Structure of Swirling Turbulent Propane Flames

Abstract

Flow structure of premixed propane-air swirling jet flames at various combustion regimes was studied experimentally by stereo PIV, CH* chemiluminescence imaging, and pressure probe. For the non-swirling conditions, a nonlinear feedback mechanism of the flame front interaction with ring-like vortices, developing in the jet shear layer, was found to play important role in the stabilisation of the premixed lifted flame. For the studied swirl rates (S = 0.41, 0.7, and 1.0) the determined domain of stable combustion can be divided into three main groups of flame types: attached flames, quasi-tubular flames, and lifted flames. These regimes were studied in details for the case of S = 1.0, and the difference in the flow structure of the vortex breakdown is described. For the quasi-tubular flames an increase of flow precessing above the recirculation zone was observed when increased the stoichiometric coefficient from 0.7 to 1.4. This precessing motion was supposed to be responsible for the observed increase of acoustic noise generation and could drive the transition from the quasi-tubular to the lifted flame regime.

Effect of High-Amplitude Forcing on Turbulent Combustion Intensity and Vortex Core Precession in a Strongly Swirling Lifted Propane/Air Flame

“…The nozzle exit diameter d was 15 mm, and d 1 and d 2 were 7 and 27 mm, respectively. The nozzle had the same geometry as in the previous studies of swirling jets and flames (Alekseenko et al, 2008(Alekseenko et al, , 2011b. The swirl rate based on the geometry corresponded to S ¼ 1.0.…”

“…Thus, the present article is devoted to a simplified objective: studying the partially premixed swirling lifted flame. According to our previous study, the presence of a combustion domain at a certain stabilization height in this regime did not fundamentally affect coherent structures in the flow near the burner nozzle exit (Alekseenko et al, 2011b). Strong perturbations were applied to the flow bulk velocity in order to force formation of ring-like vortices before the combustion domain and to investigate the effect on the combustion process.…”

“…This is usually achieved through formation of a central recirculation zone (RZ) that supplies the fresh mixture at the flame root by heat and active chemical species from the hot products. It is also noteworthy that low-swirling flames, characterized by a region of axial velocity stagnation instead of a reverse flow, also manifest a wide range of stable turbulent combustion as in the case of a strong swirl (Alekseenko et al, 2011b;Cheng, 2006;Legrand et al, 2010). Thus, flow swirling can provide stable, lean combustion regimes of premixed flames at a wide range of flow rates and can be used to reduce NOx formation (see Dunn-Rankin, 2008).…”

“…In particular, for a swirling jet flow, nonlinear dynamics of the flow itself have a significant impact on the flame reaction due to helical disturbances, vortices shedding, and changes in swirl rate. The fact that the presence of premixed combustion significantly affects the development of instabilities in the swirling shear layer of the jet and also stability of the whole flow to global modes due to significant modification of the flow pattern (e.g., see PIV data in Alekseenko et al, 2011b;Legrand et al, 2010) makes this nonlinear problem strongly dependent on combustion regime and flow geometry. Thus, the present article is devoted to a simplified objective: studying the partially premixed swirling lifted flame.…”

Heat transfer characteristics of dual swirling flame impinging on a flat surface

“…It has also been noticed from the glowing image of the dual flame that the central recirculation zone has not been extended up to the base of the flame; instead it remains up to certain distance above the exit plane of the burner. The roll-up vortex has also been observed near the top of the bluish reaction zone due to intense combustion and wrinkled flame front [51]. of swirling impinging flames due to use of different burner designs and burning conditions [33,34].…”