Disruptive and Micro-Explosive Combustion of Free Droplets in Highly Convective Environments

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Abstract
Experinlental evidence is presented showing the existence of disruptive burning for two-component fuel droplets and micro-explosive combustion for water-in-singlc fuel component emulsificd drops subjected to high relative velocities ranging from 16 to 19 m/sec. Reynolds numbers, based on the high temperature (1200-1400 K) convective freestream conditions and droplet diameter, exceedcd 40. Calculations using the one-third averaging rule suggested by other investigators for evaluating the relevant properties lead to Reynolds numbers exceeding 135. The fuels considered in this study were a solution of 50 vol.% 11-hexane-50 vol.% n-hexadecane and water-in-11-hexadecane cniulsions, with 9 and 18 percent (volume) of water. The substantial decrease i n time from ignition-to-disruption (with increased relative gas-droplet velocity) in combination with the observcd "droplet-shoulder-orientcd disruptions" for. Ihe multi-component solulion supports the existence of a toroidal vortex-like structure within thc liquid phase. Furthermore, the observed micro-explosive behavior of the water-in-n-hexadecane emulsified fuel drop-lets under highly convecrivc conditions indicates that water and fuel are not vaporizing independently of each other. In addition, the intensity of the micro-explosive event for the emulsified fuels considered does not appear to be inhibited by the high relative gas-droplet velocilies.