Observations on the combustion of boron slurry droplets in air

Abstract

Single fiber-supported slurry droplets composed of boron in JP-10 were ignited and burned in room-temperature air. Initial droplet diameters ranged from 1.2 to 3.0 mm and initial boron weight fractions f from 0 to 0.7. It was observed that although the liquid fuel apparently burns completely the boron does not ignite under these experimental conditions. For the pure liquid the combustion is smooth with a measured burning-rate constant of 0.43 mm 2/s. At low f there is periodic swelling of the droplet with mildly disruptive emission of gas from the interior; the severity of this irregularity is greatest for f ≈ 0.1 and negligible for f ≳ 0.2. For f ≲ 0.4 a reduction in droplet diameter, according to a d 2 law, is observed for a period of time, followed by a burning period of essentially constant diameter. For f ≳ 0.5, the droplet diameter remains practically constant during combustion, although the measured burning time conforms to a d 2 law. These observations are compared quantitatively with theoretical predictions and are found to agree within accuracies ranging from 10% to 25%.