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Suppression of Premixed Flames by Water Mist in Microgravity: Findings From the MIST Experiment on STS-107.


pdf icon Suppression of Premixed Flames by Water Mist in Microgravity: Findings From the MIST Experiment on STS-107. (435 K)
Abbud-Madrid, A.; McKinnon, J. T.; Amon, F. K.; Gokoglu, S.

Halon Options Technical Working Conference, 14th. Proceedings. HOTWC 2004. Sponsored by: 3M Specialty Materials, Boeing, Chemical Development Studies, Inc., DuPont Fire Extinguishants, Halon Alternative Research Corp., Hughes Associates, Inc., Kidde-Fenwal, Inc., Sandia National Laboratories, SEVO Systems, Next Generation Fire Suppression Technology Program. May 4-6, 2004, Albuquerque, NM, 1-14 pp, 2004.

Keywords:

halon alternatives; halons; fire suppression; water mist; premixed flames; microgravity; space shuttle; flame fronts; burning velocity; flame propagation

Abstract:

A preliminary analysis of the results obtained from the Water-Mist Fire Suppression experiment (Mist) that flew on the STS-107 mission of the Space Shuttle is presented. The objective of Mist is to study the effects of droplet size distribution and water concentration on the burning velocity of a propagating premixed propane-air flame. Changes of the laminar flame speed and shape are used as the measure of flame suppression efficacy. Thirty-two tests were conducted with four different fuel-air equivalence ratios (0.6, 0.7, 1.0, and 1.3), two droplet size distributions (count median diameters of 20 and 30 mm), and water loadings (measured in water mass fraction) ranging from 0.0 to 0.1. The injection of water mist in microgravity resulted in a uniformly distributed and quiescent droplet cloud. Lean flames with a parabolic flame front monotonically slowed down to a steady-state velocity through the mist cloud. Small droplet size distributions are consistently more effective than larger ones in suppressing the propagation of lean flames with the effect of droplet size diminishing at the lowest burning velocities. Increased water loading always results in slower flames, with lean flames more easily suppressed than richer ones. Flame extinction was obtained for lean flames with water mass fractions under 0.05.