CONCURRENT HORIZONTAL FLAME SPREAD - THE COMBINED EFFECT OF OXIDIZER FLOW VELOCITY, TURBULENCE AND OXYGEN CONCENTRATION

Experiments have been conducted to study the transport and chemical ki netics mechanisms controlling the spread of flames over the surface of a thick solid fuel in an oxidizing gas flow moving in the direction o f flame propagation (concurrent or flow assisted flame spread). in the experiments, the solid fuel (PMMA) is unchanged, but the oxidizer gas how velocity, turbulence intensity and oxygen concentration, are syst ematically varied to determine their effect on the flame spread proces s. This is hone by measuring the rate of flame spread, flame length, s urface heat flux, exhaust gas temperature, products of combustion and soot. The results of the experiments show that the combined effect of flow velocity, turbulence intensity, and oxygen concentration has a co mplex influence on the flame spread process. The observed variation of the flame spread rate with the how parameters appears to be due to a strong influence of these parameters on the flame temperature and leng th, and on the heat flux from the flame to the solid fuel surface. Mea surements of the combustion products provide further information about how the flow parameters affect the flame length and surface heat flux . It is shown that the flame length and heat flux data can be correlat ed in terms of non-dimensional expressions derived from boundary layer analyses of the problem. The best correlation of the data is obtained for the high flow velocity and oxygen concentration cases, where comp lete combustion occurs, The flame spread rate is the outcome of the co mbined effect of the flame length and the heat flux, and it is shown t hat the experimental data are correlated well with an expression deriv ed from a heat transfer analysis of the problem and the nondimensional expressions for the surface heat flux and flame length. The experimen ts have yielded results that are potentially important not only in the modeling and prediction of flame spread in corridors, but also in oth er aspects of fire development and testing such as burning rates, flam e lengths and combustion completeness.