Space-Based Microgravity Experiments on Flame Spread over Randomly Distributed n-Decane-Droplet Clouds: Overall Flame-Spread Characteristics
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.