A Model of Opposed Flow Flame Spread Over Charring Materials

Published

July 25, 2002

Author(s)

A A. Atreya, Howard R. Baum

Abstract

This paper presents a theoretical decsription of a diffusion flame spreading against the wind on a semi-infinite charring solid. It extends the previous flame spread models on vaporizing solids to charring materials like wood and provides a more realistic description of the gas phase. To make the problem analytically tractable, a mixture fraction approach is used in the gas phase and the no-slip condition is violated for x < 0. In the solid phase, the charring solid is assumed to decompose abruptly (endothermically or exothermically) into char and fuel gases at a specified char temperature. The steady state coupled elliptic equations for conservation of energy, mixture fraction and momentum in the gas phase and conservation of energy in the char and the pristine solid are solved by using orthogonal parabolic coordinates. A more general analytical solution is presented that reduces to deRis' flame spread formula in the limit of zero char thickness with similar assumptions. The growing char layer in the solid phase has considerable influence on the flame spread rate. It is seen that formation of a thicker char layer significantly retards the spread rate.

Citation

U. S. Combustion Institute Meeting

Volume

29

Pub Type

Journals

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Keywords

charring materials, combustion, fire research, flame spread, fluid mechanics, laminar flow

Citation

Atreya, A. and Baum, H. (2002), A Model of Opposed Flow Flame Spread Over Charring Materials, U. S. Combustion Institute Meeting, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=861133 (Accessed May 9, 2025)