Spontaneous Ignition of Thermally Thin and Intermediate PMMA Exposed to Linearly Increasing Thermal Radiation

Spontaneous ignition characteristics of thermally thin and thermally intermediate PMMA (polymethyl methacrylate) under linearly increasing heat flux (HF) are experimentally studied in this work utilizing a heating apparatus capable of flexibly controlling the radiation intensity. Ignition time, critical temperature, surface and in-depth temperatures of 1.5 and 6 mm PMMA at six sets of HFs were recorded in the tests. The corresponding measured values are estimated by numerical simulations considering the thermal decomposition of solid and insulation layer, and critical temperature is used as the ignition criterion. The results shown that the influences of insulation layer and solid pyrolysis on surface temperature are limited and significant, respectively. Thinner sample and larger HF growth rate lead to higher ignition temperature and shorter ignition time. Two stages are identified according to pyrolysis temperature prior to ignition. The measured critical temperature is 695.53 ± 16 K. Nonetheless, a more reasonable uncertainty range ± 30 K is suggested to interpret the variation of measured ignition time based on the simulation results.