Influence of Fingering Instability on Flame Spread Characteristics in a Narrow Space

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  • フィンガリング不安定性が狭い空間における燃え拡がり挙動に及ぼす影響
  • フィンガリング フアンテイセイ ガ セマイ クウカン ニ オケル モエ ヒロガリ キョドウ ニ オヨボス エイキョウ

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Abstract

<p>Near-limit flame spread is a topic of extensive fire research, and recent studies pointed out that near-limit flame spread characteristics were significantly affected by flame instability. This study considers opposed-flow flame spread in a narrow channel, in which oxygen supply by natural convection is suppressed, leading to near-limit conditions. Fingering instability appears when the oxidizer flow velocity or the channel height is small. A major objective of this study is to numerically examine the influence of fingering instability on the flame spread velocity and the extinction limit. Three-dimensional basic equations are first developed and then reduced to two-dimensional ones considering the narrowness of the domain. Numerical solutions of the two-dimensional model, in particular, fingering patterns and flame spread velocities are compared with previous experimental data, and reasonable agreement between them is confirmed. Traveling wave solutions for one-dimensional basic equations are then obtained and compared with the corresponding two-dimensional solutions. It is found that the two-dimensional flame spread velocity is faster than the one-dimensional value because the reaction is enhanced by instability. It is also found that two-dimensional flame spread is possible under certain conditions for which extinction occurs in one-dimensional flame spread. Dependence of flame spread velocity and extinction limit on model parameters is finally discussed based on predictions of the one-dimensional model.</p>

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