Experimental investigation of upstream flame propagation during boundary layer flashback of swirl flames
Experimental investigation of upstream flame propagation during boundary layer flashback of swirl flames
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DOI：
10.1016/j.combustflame.2016.03.027
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发表时间：
2016-06-01
影响因子：
4.4
通讯作者：
Clemens, Noel T.
中科院分区：
文献类型：
--
作者：
Ebi, Dominik;Clemens, Noel T.
在带有中心体混合管的模型燃烧室中研究了甲烷-氢气-空气稀薄预混湍流旋流火焰的边界层回火。我们工作的重点是提高对回火过程中流动-火焰相互作用的理解。我们结合联合收割机高速化学发光成像，立体和断层粒子图像测速仪，和三维火焰前重建技术，以揭示时间分辨，体积速度场在回火过程中的火焰前附近。我们发现了两种不同的方式，其中火焰前锋沿沿着中心体壁向上游传播。第一种模式涉及到小规模的凸起反向传播到的方法流，类似于通道流闪回，但被发现不是一个占主导地位的传播机制。相反，回火主要以大规模火焰舌的形式发生，当它们向上游传播时，这些火焰舌在整体流动方向上涡旋。在这两种情况下，进近流被显著地修改，但是由此产生的速度场的规模和性质从根本上不同。在通道和旋流火焰回火中，先前发现的接近流的一个关键特征是火焰前缘上游的负轴向速度区域。然而，我们揭示，在旋流火焰的情况下，负轴向速度的区域是一个主要的旋流运动的结果，领先的火焰舌头在相反的反向流动口袋前面的小规模的凸起。在火焰舌上游的负轴向速度区域中，边界层既不分离，流体也不再循环。相反，火焰舌施加局部阻塞效应，导致接近流的显著偏转，这导致火焰舌的前侧传播进入的负轴向速度的恒定区域。(C)2016由Elsevier Inc.出版代表燃烧研究所
Boundary layer flashback of swirling turbulent lean-premixed methane-hydrogen-air flames is investigated in a model combustor featuring a mixing tube with center body. The focus of our work is on improving the understanding of the flow-flame interaction during flashback. We combine high-speed chemiluminescence imaging, stereoscopic and tomographic particle image velocimetry, and a three-dimensional flame front reconstruction technique to reveal the time-resolved, volumetric velocity field in the vicinity of the flame front during flashback. We find two different ways in which a flame front propagates upstream along the center body wall. The first mode concerns small-scale bulges counter propagating into the approach flow, similar to channel-flow flashback, but is found not to be a dominant propagation mechanism. Instead, flashback occurs primarily in the form of large-scale flame tongues swirling in the bulk flow direction as they propagate upstream. The approach flow is modified significantly in both cases, but the scale and nature of the resulting velocity fields differ fundamentally. A key characteristic of the approach flow found previously, both in channel and swirl flame flashback, is regions of negative axial velocity upstream of the flame front. We reveal, however, that in the case of swirl flames the region of negative axial velocity is the result of a primarily swirling motion ahead of the leading flame tongue in contrast to the reverse flow pockets ahead of small-scale bulges. The boundary layer neither separates nor does fluid recirculate in the negative axial velocity region upstream of the flame tongues. Instead, flame tongues impose a local blockage effect causing significant deflection of the approach flow, which results in a constant region of negative axial velocity for the leading side of the flame tongue to propagate into. (C) 2016 Published by Elsevier Inc. on behalf of The Combustion Institute.