Pyrolysis and ignition delay time of poly(methyl methacrylate) exposed to ramped heat flux

Usually, the constant heat flux is used in the previous studies of polymeric pyrolysis. However, the ramped heat flux may be more realistic under a fire condition. For further understandings of polymer pyrolysis in the early stage of fire, the influences of ramped heat flux on pyrolysis of poly(methyl methacrylate) were experimentally and theoretically investigated. Linearly and quadratically ramped heat fluxes were controlled by the output power of a radiative heater. Surface temperature, mass loss rate, and ignition time were experimentally obtained to explore the thermochemical stability of poly(methyl methacrylate) under ramped heat fluxes. A one-dimensional model was used to predict the pyrolysis process, where kinetic parameters were evaluated by a genetic algorithm. Finally, ignition criteria including critical surface temperature and critical mass loss rate were revisited. We observed that the two ignition criteria give similar ignition time when the heat flux increases fast.