Relation of opposed flow (creeping) flame spread with extinction/ignition

Zheng, Wichman, and Benard [1] provided the motivation for addressing and revisiting modeling issues in opposed flow (creeping) flame spread over melting materials. Their approach is compared here with an earlier one [2-5]. Specifically, the theoretical underpinnings of flame-spread are discussed in relation to analytical and similarity interpretation of numerical results and experiments. The focus is on the significance and selection of the forward thermal length in the solid and on the most appropriate energy balance near the flame front for deducing material properties from experiments. Finally, (a) an expression for the speed of flame spread in opposed flow over melting materials obtained from the present analysis is compared with previous analytical results in [1] and (b) a fresh look at the critical conditions for flame spread is presented. (C) 2003 The Combustion Institute. All rights reserved.