Characterization of combustion of hardwood and softwood through experimental and computer simulations

Abstract

Physical experiments and computer simulations are commonly employed to characterize and understand fire behaviour under different conditions. Many medium- to large-scale physical experiments utilize standardized wood cribs as the fire load, while corresponding computer simulations require physical and combustion properties of such fire loads. The design of physical experiments and accuracy of computational models depend heavily on the underlying combustion models. The current study proposes an improved two-step combustion model for soft and hard wood based on physical characterization of different wood samples. Two different types of wood, i.e. softwood and hardwood were characterized using cone calorimeter. Total of six cone tests were performed under irradiation levels of 30, 50 and 75 kW m-2 for each wood sample. Thermogravimetry analysis (TGA) of wood samples was carried out to estimate the combustion kinetic parameters (through different estimation methods) like activation energy, pre-exponential factor, and reaction order for numerical simulation of cone calorimeter tests. The kinetic parameters estimated through the Kissinger-Akahira-Sunose integral method were utilized to perform computer simulation of TGA and cone calorimeter in fire dynamic simulator (FDS) using one-step and two-step combustion models. Thermal degradation temperatures of both the types of wood were observed to be between of 200 and 500 ?. During whole pyrolysis process, softwood was observed to possess larger activation energy than that of hardwood. The reaction models for softwood and hardwood were found to be diffusion type with reaction order of 2-3. TGA simulation results obtained by the two-step simulation approach were found to be better than that of one-step simulation approach. In case of cone calorimeter simulations, the two-step simulation approach yielded better prediction of heat release rate and time to ignition as compared to that of the one-step simulation approach. It is expected that the present study would be helpful in large-scale FDS fire simulation involving softwood and hardwood.