Ignition behavior of cardboard fuel particles

Abstract

This paper reports infrared thermal-image-based temperature changes on cardboard fuel surfaces during ignition. Two sets of experiments were designed to separately test the effect of convective heating and radiative heating on ignition of cardboard fuel samples. An air torch was used to provide the convective heating, and a crib fire was used for the radiative heating. An infrared thermography technique developed in our laboratory was used to obtain thermal profiles/signature of the heated cardboard sample surface under two different heating rates, from which the surface temperature change was obtained as a function of heating time. We found that radiation effects increased with an increase in the cardboard sample surface area exposed to radiation while the effects from convection dominated the smaller surface area samples. This finding qualitatively explains the United States Department of Agriculture’s (USDA) original findings that millimeter diameter pine needles cannot be ignited by radiation only, even under a long duration fire generated radiant heat flux of an average 10.3 kW/m2. Our experimental results also justify the use of the cardboard fuelbeds to simulate fire behavior of large scale forest fires.