Buoyant downward diffusion flame spread and extinction in partial-gravity accelerations
- National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
- Case Western Reserve Univ., Cleveland, OH (United States)
This paper describes experimental observations of downward, opposed-flow flame spreading made under partial-gravity conditions aboard NASA research aircraft. Special apparatus and techniques for these tests are described, including schlieren imaging of dim near-limit flames. Flame-spreading and flammability limit behaviors of a thin cellulosic fuel, 1 {times} 10{sup {minus}3} g/cm{sup 2} tested at 1 atm of pressure in oxygen/nitrogen mixtures of 13-21% oxygen by volume, are described for effective acceleration levels ranging from 0.05 to 0.6 times normal earth gravity (1 g). Downward-burning flammability increases in partial gravity, with the limiting oxygen fraction falling from 15.6% oxygen in 1 g to 13--14% oxygen in 0.05--0.1 g. Flamespread rates are shown to peak in partial gravity, increasing by 20% over the 1-g value in air (21% oxygen). Partial-gravity flame-spreading results, corrected for fuel density and thickness, are consistent with results obtained at acceleration levels above 1 g in a centrifuge. The results compare qualitatively with predictions of flame spreading in buoyant flow by models that include finite-rate chemical kinetics and surface and gas-phase radiative loss mechanisms. A correlation of experimental buoyant downward flame-spread results is introduced that accounts for radiative heat losses using a dimensionless spread rate, a radiation/conduction number, and the Damkohler number, as parameters. The correlation includes data from 0.05 g to 4.25 g and oxygen-nitrogen mixtures from 14% to 50% oxygen.
- OSTI ID:
- 93323
- Report Number(s):
- CONF-940711--
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effect of gravity on laminar premixed gas combustion. I. Flammability limits and burning velocities
Lean flammability limit of downward propagating hydrogen-air flames