Understanding the differences in mass loss rate data obtained using fire propagation apparatus and controlled atmosphere pyrolysis apparatus

Radiation-driven gasification experiments that yield mass loss rate (MLR) data for coupon-sized solid samples are used widely for pyrolysis model parametrization. It is also well known that the two devices employed most frequently to generate this data, Fire Propagation Apparatus (FPA) and Controlled Atmosphere Pyrolysis Apparatus II (CAPA II), produce markedly different results for the same material, under nominally identical heat flux settings. This study investigated these differences using a wide range of materials including two types of poly(methyl methacrylate), glass-fiber-reinforced polyamide 66, and red oak at two heat flux settings of 25 and 75 kW·m -2 . Potential contributors to the differences, including in-depth radiation absorption, heat flux spatial and temporal distributions, nitrogen flow effects, heater radiation absorption by pyrolysis gases, and sample deformation, were systematically examined. The results showed that, while the differences in the in-depth radiation absorption contributed to the observed MLR differences, spatial and temporal heat flux distribution differences were another significant contributor at both heat flux settings. At 25 kW·m -2 , sample-deformation-induced changes to the back-surface boundary conditions of FPA samples were also found to be important. It was demonstrated that accounting for these effects brings the MLR data collected in FPA and CAPA II into complete agreement.