Criteria for piloted ignition of combustible solids

The onset of piloted ignition (flash point) of combustible polymers is predicted by a gas phase combustion energy density of 1.9 MJ/m3 that describes the lower flammability limit of fuel vapor–air mixtures. The mass flux (1 g/m2 s) and (virtual) heat release rate (24 kW/m2) of the solid at incipient ignition derived from this observation are in general agreement with experimental data for piloted ignition of plastics. Sustained ignition marks the transition from lower-limit to stoichiometric burning and the critical heat release rate increases proportionally to 66 kW/m2. A critical heat release rate, unique among ignition criteria, is independent of material composition because of the implicit coupling between the gas and condensed phase processes.