Piloted Ignition Times for Cellulosic Solids Exposed to Time-Dependent Heat Fluxes.

摘要

The time to piloted ignition of a cellulosic solid,when exposed to a constant incident heat flux,has been extensively studied by other researchers. Results have been interpreted by relating the ignition time to the heat flux by a transcendental equation involving the error function. For practical situations,the equation simplifies to an inverse power dependence of the ignition time on the heat flux. The present paper extends the scope of this inverse power relation by adapting it to include the effects of a varying heat flux. It then is used to predict ignition times of a wood target exposed to flames from pools of gelled hydrocarbons. Results indicate that the ignition time is inversely proportional to the hydrocarbon mass and is relatively independent of height (above the flame agent) below a height equal to the pool radius and then increases rapidly with height. Thermocouple measurements of flames from burning gelled hydrocarbons are reported. (Author)