Flame spread in a forward forced flow

Abstract

A theoretical model is developed for the propagation of flames over a solid fuel in a laminar forced oxidizing gas flow moving in the direction of flame propagation. The model makes use of a boundary-layer approximation to describe the flow and of an ignition surface temperature to define the rate of flame spread. By solving the gas-phase problem uncoupled from the solid-phase analysis in first-order approximation, analytical expressions are obtained for the velocity of propagation of the pyrolysis front and of the flame tip along thermally thick and thin fuels as functions of the thermophysical properties of the fuel and induced oxidizer flow. Experimental measurements of the rate of spread of the pyrolysis front for flames propagating over polymethylmethacrylate (PMMA) sheets are reported as a function of the velocity of a forced air flow. The experiments are performed in a small-scale wind tunnel. A laser Doppler velocimeter facility is used to record the forced-flow characteristics, and arrays of thermocouples are used to measure the rate of flame spread. It is shown that the theoretical predictions agree well with the experimental measurements.