Effect of Microgravity on the Development and Structure of Fire Whirls

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Fire whirls have long fascinated the scientific community due to their unique structure and behavior. When swirl is added to a traditional diffusion flame, a dramatic intensification of combustion occurs increasing flame lengths and burning rates, producing a more vigorous state of combustion. While fire whirls have long been studied, many aspects of their behavior remain unsolved, such as the precise mechanisms by which circulation and buoyancy interact to lengthen diffusion flames in swirling flows. Microgravity presents an opportunity to directly investigate these aspects, isolating the influence of ambient circulation from buoyancy on the flame. Results are presented from tests performed at the NASA Glenn Research Center Zero Gravity Research Facilities’ 5.18 s drop tower. Fire whirls were generated over a paraffin wax wick in 1 g using two offset half cylinders. A vertical bank of fans was placed at each inlet to provide continuous circulation, which was held constant throughout the microgravity drop test. Results show that the lengthening effect observed in 1 g dramatically reduces in microgravity, even under the influence of continuous ambient circulation. Some similarities are still observed between 1 g fire whirls with strong circulation and microgravity fire whirls, with flames shrinking and expanding into a more cylindrical form. Interesting phenomena is also observed in higher-g conditions following the drop test.