Wildland Fire Spread by Radiation-a Model Including Fuel Cooling by Natural Convection

Abstract

The spread of a line fire through wildland fuel is modeled for situations in which unignited fuel is heated by radiation and cooled by radiation and convection. The fuel bed is idealized as a continuum in a homogeneous layer composed of uniformly distributed, approximately convex particles that are randomly oriented, thermally thin, and radiometrically black. The model is implemented as an algorithm that finds the temperature of the fuel particles every-where in the unignited bed and solves simultaneously for the rate of fire spread and the shape o f the surface (the ignition interface) upon which the particles are ignited. This algorithm is an extension of one presented earlier that neglects particle cooling by convection. Results predicted by the revised model are compared to measurements made on experimental fires. The ignition interface shape predicted for the experimental fires agrees reasonably well with measuremenls when two free parameters have values chosen so as to yield the measured rate of fire spread.