Products of wood smolder and their relation to wood-burning stoves

Abstract

The smoldering combustion of solid wood is a process pertinent to both fire safety and to the generation of air pollutants in wood burning stoves; fundamental aspects of this process are examined here in order to provide insights into both of these problem areas. The wood configuration employed here was designed to permit self-sustained smolder with visual access. Tests were conducted with both red oak and white pine and both woods behaved quite similarly. In separate tests the air flow velocity was varied from about 9 to 22 cm/sec. At the low end of this range, the smoldering process was prone to extinction; at the high end it was increasingly likely to transition into flaming combustion. The smolder velocity, peak temperature, rate of heat and product evolution all increased over this flow range in an essentially linear manner. Analysis of the temperature profiles in the wood pointed to a dominance of radiative transfer in the smolder propagation process at low air flow rates and roughly equal roles for radiation and convection at higher flow rates. The principal species in the tar evolved from smoldering wood resemble, in large degree, those from previous forced wood gasification experiments and those obtained frommore » a wood stove operated in a smoldering mode. This reinforces the previous conclusion that air pollutants arise directly from wood smolder and change little in passing through the firebox of a stove. 36 refs., 27 figs., 2 tabs.« less