Flame Spread Over Combustible Surfaces for Laminar Flow Systems Part II: Flame Heights and Fire Spread Rates

Abstract

In the previous paper (Part I), results were given for unburnt fuel fraction and wall heat flux for boundary layer flows with combustion. In the present paper, a highly simplified model of the combusting plume region and the previous unburnt fuel results are used to obtain analytical results for the ratio of flame to gasification heights in terms of the parameters r and B. It is found that these analytical results can be correlated by a simple formula which depends only on the ratio r/B. These results are compared with the predictions of other theoretical work and with available experimental measurements. The flame height results and the heat flux results from Part I are then combined with a simplified physical model to obtain an explicit result for laminar flame spread on thermally thick surfaces. Using this explicit result the effects of varying parameters such as ambient oxygen concentration, heat of combustion and heat of pyrolysis on the flame spread rate are described. The importance of choosing proper initial conditions when comparing experimental data with theory is discussed, and comparisons with measurements for upward burning on vertical walls are given.