Visualization of blow-off events in bluff-body stabilized turbulent premixed flames
Visualization of blow-off events in bluff-body stabilized turbulent premixed flames
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DOI：
10.1016/j.proci.2010.05.044
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
J. Dawson;R. Gordon;J. Kariuki;E. Mastorakos;A. Masri;M. Juddoo
中科院分区：
文献类型：
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作者：
J. Dawson;R. Gordon;J. Kariuki;E. Mastorakos;A. Masri;M. Juddoo
在直径d=25 mm的轴对称钝体上稳定的受限和非受限湍流甲烷-空气贫油预混火焰已被检查接近吹出极限和在熄灭瞬态期间，与OH荧光化学发光，火焰层析成像和OH-PLIF在5 kHz下操作，允许吹出事件的持续时间的量化。随着总速度的增大或当量比的减小，火焰逐渐接近吹离，随着长度的减小，火焰形状由圆锥形逐渐变为圆柱形。接近吹离时，火焰在轴线上闭合，长度约为2d，在吹离条件之前，火焰呈“M”形，反应锋位于回流区（RZ）内。在吹离事件，新鲜的反应物进入的RZ从向前的停滞区域和显着的火焰发生碎片，与分支的火焰保持锚定在钝体边缘和单独的火焰口袋内随机移动的RZ。随着这些火焰碎片的逐渐消除，发生了总体吹离。在约15 d/Ub的时间段内，随着火焰表面的减小，累积的OH-2排放缓慢地减小到零。结果表明，在再循环火焰中的吹脱事件持续时间较长的停留时间在RZ和结构的火焰接近灭绝支持背后的基本假设搅拌良好的反应器概念吹脱。
Confined and unconfined turbulent methane-air lean premixed flames stabilized on an axisymmetric bluff-body of diameter d=25 mm have been examined close to the blow-off limit and during the extinction transient, with OH∗chemiluminescence, flame tomography and OH-PLIF operated at 5kHz, allowing a quantification of the duration of the blow-off event. Blow-off was approached by increasing the bulk velocity Ubor decreasing the equivalence ratio and the flame shape changed from conical to cylindrical with decreasing length. Close to blow-off, the flame closed on the axis and was about 2d long, and just before the blow-off condition it took an “M” shape with reaction fronts inside the recirculation zone (RZ). During the blow-off event, fresh reactants entered the RZ from the forward stagnation region and significant fragmentation of the flame occurred, with branches of the flame remaining anchored on the bluff-body edge and separate flame pockets moving randomly inside the RZ. Overall blow-off occurred with the gradual elimination of these flame fragments. The integrated OH∗emission decreased slowly to zero as the flame surface decreased over a period of about 15d/Ub. The results suggest that the blow-off event in recirculating flames lasts long compared to the residence time in the RZ and the structure of the flame close to extinction supports the underlying assumptions behind well-stirred reactor concepts of blow-off.