Flame spread criteria

Theoretical studies are primarily concentrated on the treatment of flame blow-off phenomenon and the prediction of flame spreading rates. Dunskii [12] is apparently the first to put forward the phenomenological theory of flame stabilization. The theory is based on the characteristic residence and combustion times in adjoining elementary volumes of fresh mixture and combustion products in the recirculation zone. It was shown in [13] that the criteria of [1, 2, 5] reduce to Dunskii s criterion. Longwell et al. [14] suggested the theory of bluff-body stabilized flames assuming that the recirculation zone in the wake of the baffle is so intensely mixed that it becomes homogeneous. The combustion is described by a second-order rate equation for the reaction of fuel and air. 

It is of interest to know under what conditions opposed-flow flame spread ceases. Quintiere and Harkleroad proposed the minimum surface temperature for spread, Ts min, as a convenient criterion.38... 

In Refs. an analytical solution of the two-dimensional problem of flame spread over a horizontal surface is described. Formulas for the determination of the location of the chemical reaction, fuel flow to the latter, and temperature in the reaction zone have been derived. From these formulas it follows that the distance between the material surface and the chemical reaction zone is greater farther away from the flame front. Also the influx of fuel and oxidant to the reaction zone is smaller and the temperature is higher, and attains in the limit a level corresponding to adiabatic combustion. Thus, the temperature in the flame front may be substantially below the adiabatic temperature of combustion because of heat transfer to the combustible material. A criterion determining the effect of the gas-phase reaction rate on the com-... 

The criterion of flame spread over a polymeric material surface may be expressed as follows ... 

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