- Author
-
Apte, V. B.
|
Bilger, R. W.
|
Green, A. R.
|
Quintiere, J. G.
- Title
- Wind-Aided Turbulent Flame Spread and Burning Over Large-Scale Horizontal PMMA Surfaces.
- Coporate
- Sydney Univ., Australia
Londonderry Occupational Safety Center, Australia
National Institute of Standards and Technology, Gaithersburg, MD
- Journal
-
Combustion and Flame,
Vol. 85,
No. 1-2,
169-184,
1991
- Keywords
-
polymethyl methacrylate
|
turbulent flames
|
flame spread
|
heat flux
|
flame length
|
pyrolysis
|
heat release
|
thickness
|
flame velocity
|
wind tunnels
- Abstract
- Measurements of concurrent fire spread and burning over horizontal polymethylmethacrylate (PMMA) surfaces exposed to air flows ranging from 1 to 2.1 m/s in a 2.4 m x 5.4 m wind tunnel are presented and analyzed. The fire propagation occurs in two successive modes. In the first mode, when the flame is confined within a boundary layer, the pyrolysis mass loss flux is essentially constant. Transition to the second mode, occurring earlier at lower wind velocities, is accompanied by a rapid increase in the pyrolysis flux because the flame stands up into a plume. For the first boundary layer mode, the flame is an order of magnitude thicker than the theoretical turbulent boundary layer over a flat plate due to upward buoyancy and blowing effects. The measured flame spread rate in the first mode increases during propagation and is independent of the wind velocity [equation]. Over the whole range of data, the flame length [equation] is approximately 1.25 times the pyrolysis length. A correlation of [equation] in terms of the energy release rate [equation] shows [equation] in the second mode. As the fire propagets, radiation increasingly becomes the dominant mode of heat transfer from the flame to the fuel surface. Predictions of the spread velocity using Quintiere's [J. Res. Natl. Bur. Stand. 93:61-70 (1988)] model follow the trend in the measurements reasonably well, though the actual predictions are sensitive to the uncertain material property values.