Combustion of single droplets and droplet pairs in a vibrating field under microgravity

Acoustic effects on combustion of single droplets and droplet pairs in microgravity were experimentally studied using octane as fuel and ambient gas (air) at 1 atm and atmospheric temperature. For single droplets, at low frequency and small to moderate acoustic intensities, the evaporation rate increased, with the burning rate constant nearly proportional to the product of frequency and square of displacement. The burning rate constant at higher acoustic intensities either remained constant or decreased. In some cases, flame extinction occurred at a finite droplet diameter. For a droplet pair, the burning rate constant was consistently lower than the single droplet. The burning rate constant reached a maximum at an intermediate acoustic intensity at lower frequencies. The flame size decreased due to interactions, as did the critical spacing indicating a merged flame around the droplet pair vs. individual flames surrounding the droplets. Interactions stabilized the flame, in that droplet pair burn to completion under conditions where the flame surrounding a single droplet extinguished at a finite droplet diameter. Original is an abstract.