Radiant flux density, energy density and fuel consumption in mixed-oak forest surface fires

Abstract

Closing the wildland fire heat budget involves characterising the heat source and energy dissipation across the range of variability in fuels and fire behaviour. Meeting this challenge will lay the foundation for predicting direct ecological effects of fires and fire–atmosphere coupling. In this paper, we focus on the relationships between the fire radiation field, as measured from the zenith, fuel consumption and the behaviour of spreading flame fronts. Experiments were conducted in 8 × 8-m outdoor plots using preconditioned wildland fuels characteristic of mixed-oak forests of the eastern United States. Using dual-band radiometers with a field of view of ~18.5 m2 at a height of 4.2 m, we found a near-linear increase in fire radiative energy density over a range of fuel consumption between 0.15 and 3.25 kg m–2. Using an integrated heat budget, we estimate that the fraction of total theoretical combustion energy density radiated from the plot averaged 0.17, the fraction of latent energy transported in the plume averaged 0.08, and the fraction accounted for by the combination of fire convective energy transport and soil heating averaged 0.72. Future work will require, at minimum, instantaneous and time-integrated estimates of energy transported by radiation, convection and soil heating across a range of fuels.