A preliminary investigation of the effect of water mists on premixed flame propagation in a cylindrical tube under low-gravity conditions has been conducted to define the scientific and technical objectives of the experiments to be performed on the Space Shuttle and International Space Station microgravity environments. The inhibiting characteristics of water mists in propagating flames of propane-air mixtures at various equivalence rations are studied. The effects of droplet size and concentration on the laminar flame speed are used as the measure of fir suprression efficacy. Flame speed and propagation behavior are monitored by a video camera. Reduced gravity is obtaind with an aircraft flying parabolic trajectories. Measurements and quanitative observations from the low-gravity experiments clearly show the effect of water mist on flame speed abatement, flame shape, and radiant emission. For lean propane-air mixtures, the flame speed increases at first with low water-mist concentrations and then decreases below its dry value when higher water-mist volumes are introduced in the tube. This phenomenon may be due in part to the heating of the unburned mixture ahead of the flame as a result of radiation absorption by the water droplets. For rich propane-air mixtures, similar bhavior of flame speed vs. water concentration is encontered but in this case is mostly due to the formation of cellular flames. At high water loads both lean and rich flames exhibit extinction before reacing the end of the tube.
展开▼
