Research Initiation Awards: Spherically-Symmetrical Combustion of Unsupported Droplets Under Normal-Gravity Conditions

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A unique drop-tube experimental apparatus to promote spherically-symmetric evaporation and combustion of freely- falling droplets will be developed and constructed. The design of the apparatus is based upon the principle that gravitationally-induced pressure gradients in gases may be significantly reduced by accelerating the gases with properly contoured tubes. Droplets traveling with the gases will experience greatly reduced buoyancy and forced convection environments, thereby promoting spherical symmetry. The apparatus will be used to study nearly spherically-symmetrical droplet evaporation and combustion under conditions that have heretofore not been experimentally achieved (i.e., combustion of droplets initially = 100 um in diameter at atmospheric pressure). Experimental studies will focus on 1. combustion and extinction of hydrocarbon droplets, 2. measurements of transient droplet and flame diameters, and 3. combustion and disruption of droplets with strong sooting tendencies. The proposed facility will allow many fundamental and practical droplet combustion and evaporation phenomena to be studied under conditions previously unattained. The data obtained will be useful for testing existing theories, and will provide fundamental information on phenomena such as extinction conditions, transient vaporization rates, and transient flame growth. Results from the work will be useful to the scientific community (from the fundamental information gained), and also to the combustion and spray communities in general, possibly allowing improved practical combustion devices to be developed.