FLAME SPREAD OVER THIN SOLID FUELS IN PARTIALLY PREMIXED ATMOSPHERES

Experiments on flame spread rates (S-f) over thin solid fuels in oxidi zing atmospheres to which gaseous fuel is added reveal a large increas e in S-f for some gaseous fuels. The most to least effective fuels tes ted are, in order, H-2, CO, hydrocarbons, and NH3. From these experime nts it is inferred that, unlike nonpremixed flame spread, the finite-r ate kinetics of the gaseous fuel have a dominant influence on S-f even far from extinction conditions. A simple model developed to account f or the effect of the gaseous fuel on S-f, while still retaining the fr amework of deRis's model of S-f for infinite-rate kinetics of the soli d fuel vapors, shows good qualitative and fair quantitative agreement with experimental data. Furthermore, it is shown that for some fuels, e.g., CO, the gaseous products of partial combustion produce a more co mbustible environment than the fresh atmosphere; the practical implica tions of this finding for modeling fires in enclosures are discussed.