Flame spread over thin solid fuels in partially premixed atmospheres,

Experiments on flame spread rates (Sf) over thin solid fuels in oxidizing atmospheres to which gaseous fuel is added reveal a large increase in Sf for some gaseous fuels. The most to least effective fuels tested are, in order, H2, CO, hydrocarbons, and NH3. From these experiments it is inferred that, unlike nonpremixed flame spread, the finite-rate kinetics of the gaseous fuel have a dominant influence on Sf even far from extinction conditions. A simple model developed to account for the effect of the gaseous fuel on Sf, while still retaining the framework of deRisʹs model of Sf for infinite-rate kinetics of the solid 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 combustible environment than the fresh atmosphere; the practical implications of this finding for modeling fires in enclosures are discussed.