Citation

Olson SL, T'Ein JS. Fire Mater. 1999; 23(5): 227-237.

Copyright

(Copyright © 1999, John Wiley and Sons)

DOI

unavailable

PMID

unavailable

Abstract

Large-scale buoyant low stretch stagnation point diffusion flames over a solid fuel (polymethylmethacrylate) were studied for a range of aerodynamic stretch rates of 2-12 s(-1) which are of the same order as spacecraft ventilation induced stretch in a microgravity environment. An extensive layer of polymer material above the glass transition temperature,vas observed. Unique phenomena associated with this extensive glass layer included substantial swelling of the burning surface, in-depth bubble formation, and migration and/or elongation of the bubbles normal to the hot surface. The bubble layer acted to insulate the polymer surface by reducing the effective conductivity of the solid. The reduced in-depth conduction stabilized the dame for longer than expected from theory neglecting the bubble layer. While buoyancy acts to move the bubbles deeper into the molten polymer, thermocapillary forces and surface regression both act to bring the bubbles to the burning surface. Bubble layers may thus be very important in low gravity (low stretch) burning materials, As bubbles reached the burning surface, monomer fuel vapours jetted from the surface, enhancing burning by entraining ambient air flow. Popping of these bubbles at the surface can expel burning droplets of the molten material, which may increase the fire propagation hazards at low stretch rates.