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On the critical conditions for pool-fire puffing

机译：在扑火的临界条件下

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Pool fires are known to undergo a bifurcation to a globally unstable puffing state driven by baroclinic and buoyant vorticity production. Although the supercritical puffing regime away from the bifurcation has been studied extensively in the literature, no detailed account has been given of the critical conditions for its onset, that being the purpose of the present paper. For the relevant canonical case of round liquid pools without swirl, aside from the inherent thermochemical and transport parameters associated with the fuel, pool-fire puffing is governed by a single dimensionless number, the Rayleigh number, which scales with the cube of the pool diameter. Consequently, for a fixed fuel and under fixed ambient conditions, there is a critical fuel pool diameter, associated with a critical value of the Rayleigh number, above which the flame starts puffing. A global linear stability analysis that accounts for the axisymmetry of the prevailing instability mode is developed here to describe the bifurcation. The mathematical formulation employs the limit of infinitely fast reaction, with account taken of the nonunity Lewis number and vaporization characteristics of typical liquid fuels. Predictions of critical puffing conditions, including critical diameters and puffing frequencies, are provided for methanol and for heptane pool fires, and the results are compared with results of new small-scale experiments under controlled laboratory conditions, reported here, yielding reasonably good agreement. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：已知池火会因气压斜升和浮力涡旋的产生而分叉成整体不稳定的膨化状态。尽管在文献中已经广泛研究了远离分叉的超临界膨化状态，但是没有详细说明其开始的临界条件，这是本文的目的。对于没有旋涡的圆形液体池的相关典型情况，除了与燃料相关的固有热化学和运输参数外，池喷火还由单个无量纲数瑞利数控制，瑞利数随池直径的立方而缩放。因此，对于固定的燃料和在固定的环境条件下，存在与瑞利数的临界值相关的临界燃料池直径，在该直径以上，火焰开始喷出。在此开发了一个全局线性稳定性分析，该分析解释了当前不稳定模式的轴对称性，以描述分叉。数学公式采用了无限快速反应的极限，并考虑了典型液体燃料的路易斯路易斯数和汽化特性。提供了甲醇和庚烷池火灾的临界抽吸条件的预测，包括临界直径和抽吸频率，并将结果与​​此处报道的在受控实验室条件下进行的新的小型实验的结果进行了比较，得出了很好的一致性。 （C）2018年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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