Correlations for Evaluation of Flame Spread over an Inclined Fuel Surface

Abstract

The time-dependent flame spread process over thermally thick slabs of polymethyl methacrylate (PMMA) is investigated with particular emphasis on the burning behavior and geometry of the flame. 10 cm wide by 20 cm long samples are ignited and allowed to spread upwards at angles of orientation between pool and ceiling burning. Correlations between the flame length and the fuel mass-loss rate have revealed a delayed transition to turbulence for flames residing on the underside of fuel samples, and an earlier transition to turbulence for flames on the topside of these samples, compared to traditional vertical wall flames. As the fuel inclination increases, the relationship between the flame length and fuel mass-loss rate ranges between a recent theoretical prediction for a laminar wall plume dominated by diffusion and the traditional prediction for a turbulent wall plume dominated by convective mixing. The buoyancy-induced flow field, characterized by the flame tilt angle is shown to correspond to previously-found modifications of heat-flux profiles ahead of the flame front, which control flame spread, and the heat flux to the burning surface of the fuel, which controls fuel mass-loss rates. Other correlations between some of these parameters, such as the flame and pyrolysis lengths are also presented as a function of inclination.