A further study on effects of external thermal radiation on flame spread over paper

• Published in: Combustion and flame 1978, Vol.32, p.95-105
• Main Authors: Hirano, Toshisuke, Tazawa, Koichi
• Format: Article
• Language: English
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/0010-2180(78)90083-4

An experimental study has been conducted to elucidate the mechanism by which the spread rate of a stable, downward-spreading flame over paper increases with the increase of the radiant flux from an external heat source. The gas velocity and temperature profiles near the leading flame edges under various external radiant fluxes were examined by using particle tracer techniques and fine wire therm ocouples. Velocity profiles in front of the leading flame edge were greatly influenced by the external thermal radiation. As the external radiant flux was increased, the gas-stream velocity upstream of the leading flame edge increased and the deceleration of the gas stream approaching the leading flame edge became intense. Temperature profiles near the leading flame edge also were greatly influenced by the external thermal radiation. At the station 0.2 cm ahead of the pyrolysis front the temperature gradient at the paper surface in the direction normal to it decreased as the external radiant flux was increased, while at the station just ahead of the pyrolysis front the temperature gradient increased with the external radiant flux. Although the preheat zone width decreased with the increase of external radiant flux, the net heat flow to the unburned material through the gas phase increased. The increase of the flame spread rate with increasing external radiant flux could be attributed not only to the increase of the unburned material temperature but also to the increase of the rate of gas-phase heat transfer from the flame zone to the unburned material.