Ignition wave propagation and release of volatiles in beds of wood particles

Ignition wave propagation against the air flow is studied in different packed beds of wood fuels both experimentally and theoretically. Observed trends can be predicted with the model when moisture, bed density and air rate vary. The geometrical factors, such as particle shape, size and orientation are lumped to a single experimental parameter for heat transport in the bed.

The main factors affecting the ignition velocity are fuel moisture content, fuel volatile content, air flow rate through the bed, air temperature, bulk density of the fuel bed, particle size, and particle shape. The ignited mass flow rate of dry solids per unit area of the bed (velocity of the ignition front x bed density( is an important parameter, when designing combustion equipment, since it is proportional to the release rate of the volatiles from the grate area and the energy/grate area obtained from the combustion of volatiles. Different factors (fuel, moisture, particle size, bed porosity) affecting the ignited mass flux and release of volatiles are discussed.