A STUDY OF INTERMITTENT CONVECTIVE HEATING OF FINE LIVE WILDLAND FUELS

Abstract

Recent studies have investigated the role of convective heating advancing wildland fire spread through intermittent bursts or pulses of flames onto unburned fuels. This study seeks to expand on initial experiments investigating the role of this intermittent convective heating by exploring the ignition of live fuels with different moisture contents under these conditions. A modified Rubens' tube is used to generate periodic pulses of a small-scale diffusion flame over the surface of a fuel sample. Infrared imaging is used to track the surface temperature of the fuel leading up to ignition while the intermittent temperature is characterized using a fine-wire thermocouple. Ponderosa pine needles with a variety of moisture contents are tested at different heating frequencies to determine patterns in the process of ignition. The fuel moisture content is seen to have a significant effect on the ignition times of fuels, while the temperature at ignition is seen to vary with heating frequency. Ignition results are compared with past tests of dried dead fuels using the same apparatus. Model predictions of ignition times as a function of ignition temperature and moisture content are also compared to experimental values and discussed.