An investigation of the effect of water mists on premixed flame propagation in a cylindrical tube under reduced-gravity conditions has been conducted to define the scientific and technical objectives of the experiments to be performed in the Space Shuttle and International Space Station microgravity environments. The inhibiting characteristics of water mists in buoyancy-free propagating flames of propane-air mixtures at various equivalence ratios are investigated. The effects of droplet size and concentration on the laminar flame speed and flame shape are used as the measure of fire suppression efficacy. Reduced gravity is currently obtained in the NASA KC-135 aircraft flying parabolic trajectories. Two different types of flame behavior are found depending on the mixture stoichiometry. In the case of lean -air mixtures, the flame speed initially increases with low water mist concentrations and then decreases below its dry value when higher water mist volumes are introduced in the tube. For rich -air mixtures, similar behavior of flame speed vs. water concentration is encountered but in this case is mostly due to the formation of cellular flames which acquire higher temperatures and consequently become more resistant to extinction by the water mist. The character of the mist aerosol (droplet size distribution, concentration and wall deposition rate) as a function of time and position is also investigated. It is suspected that the unusual flame behavior may be due in part to the short duration and low quality of the reduced gravity available in the KC-135 aircraft. Consequently, the next stage of the Water Mist Fire Suppression project (Mist) is the development of an experiment that will take advantage of the long duration and high-quality microgravity experienced in orbital flight. The final objective is to create a detailed map of flame speed, droplet diameter, water concentration, and equivalence ratio, which will give the appropriate set of parameters for flame suppression.
The water-mist fire suppression experiment: Recent ground-based results and planned space experiments
SPACE TECHNOLOGY AND APPLICATIONS INTERNATIONAL FORUM - 2000 ; 2000 ; Albuquerque, New Mexico (USA)
AIP Conference Proceedings ; 504 , 1 ; 402-407
2000-01-19
6 pages
Conference paper
Electronic Resource
English
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