Quantifying the heat release from char oxidation in timber

Abstract

To improve our understanding of the energy balance in the burning of timber it is necessary to quantify the heat release contribution of char oxidation. Experiments were performed in the Fire Propagation Apparatus at 0%, 15%, and (ambient) 21% O2 environments to analyse the individual contributions of pyrolysis, char oxidation, and flaming to the total heat release of burning timber. During piloted steady state burning under a heat flux of 30 kW/m2 the contribution of char oxidation was found to be 59% of the total heat release rate. During unpiloted steady state burning under a heat flux of 60 kW/m2, the contribution of char oxidation was found to be 43%. From the energy released by char oxidation, 5–8% of this promoted further pyrolysis – with the remaining 92–95% lost to the surrounding environment. It was found that 45–60% of the increase in mass loss is due to additional pyrolysis. The mass loss rate of timber during burning is partly due to pyrolysis, and partly due to char oxidation. Under the conditions tested, it was found that for every 1g of pyrolysis between 0.3g and 0.6g of additional mass loss was incurred due to the presence of char oxidation.