Abstract
The influence of tube vortex structure on flow fields and combustion characteristics in swirl-stabilized methane-pulverized coal flames was investigated experimentally. The detailed flame structures, such as the inner recirculation zone (IRZ) and exhaust tube vortex (ETV), were observed via particle image velocimetry (PIV) using various swirl combinations. The appearance of the ETV structure in the swirl-stabilized flame was an attractive flame to reduce NOx emissions that was shown to be associated with the oxygen-deficient and fuel-rich atmosphere similar to the environment of the IRZ. The flow fields of the swirl-stabilized flame were divided into four regions (zone (1): IRZ region; zone (2): stagnation region; zones (3) and (4): transition regions). For the co-swirling coal flames with swirl conditions of Sco = 0.9 and 1.3, relatively uniform patterns of the root-mean-square of the axial velocity fluctuation (u′rms) appeared between the IRZ and ETV, including zone (2). In addition, the ratio of the strain rate from the velocity gradient (SR) of zones (3) and (4) converged between 35% and 40% in the co-swirling flames with swirl conditions of Sco = 0.9 and 1.3. These parameters were strongly correlated with the generation of the ETV flame. The effects of the swirl intensity and swirl arrangement on the flame stability and combustion characteristics were investigated with regard to the ETV flame.
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