Space-Based Microgravity Experiments on Flame Spread over Randomly Distributed n-Decane-Droplet Clouds: Overall Flame-Spread Characteristics
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This research conducted microgravity experiments on the flame spread over randomly distributed n-decane-droplet clouds aboard the Japanese Experiment Module “Kibo” on the International Space Station. 67-152 droplets were distributed at intersections of a 30 × 30 square lattice with 14-micron SiC fibers placed in a combustion chamber. One droplet on the bottom side of lattice was ignited by a hot-wire igniter to start the flame spread. The burning behavior was observed by a digital camera. This paper is the first to report the group-combustion excitation of randomly distributed droplet clouds through flame spread and its dependence on the mean droplet spacing of the droplet cloud. The results show that there exists the group-combustion-excitation-limit mean droplet spacing. The flame-spread behavior is significantly affected by the initial conditions around the group-combustion-excitation limit, where the burning lifetime of the droplet cloud attains maximum and an interesting phenomenon, such as large-scale ignition, occurs. The group-combustion-excitation-limit mean droplet spacing is greater than the flame-spread-limit droplet spacing of the linear droplet array. The overall flame-spread rate of the droplet cloud is equivalent to or slightly greater than the flame-spread rate of the linear droplet array.
KeywordsFlame spread Droplet cloud Group combustion Microgravity
This research was conducted as Kibo utilization experiments called “Group Combustion” by JAXA. We wish to thank Mr. N. Motomatsu, Mr. K. Iwai, and Mr. K. Nagata for their help in the experiments.
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