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首页> 外文期刊>Combustion and Flame >Effect of the length of a plate flame holder on flame blowout limit in a micro-combustor with preheating channels
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Effect of the length of a plate flame holder on flame blowout limit in a micro-combustor with preheating channels

机译：板式火焰保持器的长度对带有预热通道的微型燃烧器中火焰喷出极限的影响

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It is challenging to achieve a large blowout limit for micro-combustors due to the increased heat loss ratio and reduced residence time. For this, we recently developed a micro-combustor with a plate flame holder and two preheating channels. In this paper, the effect of the plate length (L-b = 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 mm) on the blowout limit of CH4/air flames was numerically investigated. The results show that the flame blowout limit increases firstly and then decreases with an increasing plate length. The largest blowout limit is obtained at L-b = 1.0 mm. Three neighboring cases, i.e., L-b = 0.5, 1.0 and 2.0 mm, are taken to analyze the underlying mechanisms responsible for this non-monotonic trend. The flame blowout process demonstrates that, the flame is extinguished due to "pinch-off phenomenon" at high inlet velocity, and the shorter the distance between the upper and lower flame fronts, the smaller the blowout limit will be. Numerical analysis reveals that the differences in flame blowout limits are a result of the combined effects of heat recirculation and local flow field at the entrance of the combustion chamber. The heat recirculation effect grows stronger with a decreasing length of flame holder, which results in a more obvious volumetric expansion at the entrance of the combustion chamber. Meanwhile, the plate flame holder has a redirection effect on the local flow field. As a result, the gaseous mixture enters the combustion chamber with a smallest acute angle in the case of L-b = 1.0 mm, which leads to a largest distance between the upper and lower flame fronts and a longest recirculation zone. Consequently, the flame blowout limit reaches a peak at L-b = 1.0 mm. The present work provides an important guideline to design such kind of micro combustors. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：由于增加的热损失率和减少的停留时间，要使微型燃烧器达到较大的爆燃极限是具有挑战性的。为此，我们最近开发了一种带有平板火焰支架和两个预热通道的微型燃烧器。在本文中，数值研究了板长（L-b = 0.5、1.0、2.0、3.0、4.0、5.0和6.0 mm）对CH4 /空气火焰的爆破极限的影响。结果表明，随着板长的增加，火焰喷出极限先增大然后减小。最大吹出极限在L-b = 1.0 mm时获得。采用三个相邻的情况，即L-b = 0.5、1.0和2.0 mm，来分析造成这种非单调趋势的潜在机制。火焰喷出过程表明，在高入口速度下，火焰由于“夹断现象”而熄灭，上下火焰前沿之间的距离越短，喷出极限将越小。数值分析表明，火焰喷出极限的差异是热循环和燃烧室入口处的局部流场共同作用的结果。随着火焰保持器长度的减小，热循环效果会增强，从而导致燃烧室入口处的体积膨胀更明显。同时，板式火焰保持器对局部流场具有重定向作用。结果，在L-b ＝ 1.0mm的情况下，气体混合物以最小的锐角进入燃烧室，这导致上下火焰前沿之间的距离最大以及最长的再循环区域。因此，火焰吹出极限在L-b ＝ 1.0mm处达到峰值。本工作为设计这种微型燃烧器提供了重要的指导。 （C）2016年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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