Flame spread of droplet-cloud elements with two-droplet interaction in microgravity

This research conducted microgravity experiments to investigate the flame-spread characteristics of the fuel-droplet-cloud element with uneven droplet spacing, which is a basic element of a randomly distributed droplet cloud at the critical condition for group-combustion occurrence. Flame spread to a droplet followed by burning with two-droplet interaction was observed in microgravity to investigate the effect of flame-spread direction and local interactive effect. The results show that the flame-spread rate to a droplet in a perpendicular direction to the axis of two interacting droplets was greater than that to the droplet in the same direction as the axis of two interacting droplets. The temperature distribution around burning droplets was measured by the Thin Filament Pyrometry (TFP) method based on radiation from 14-micron SiC fibers suspending droplets at their intersections. The flame-spread-limit distance increased with two-droplet interaction in both flame-spread directions. This also shows the dependence of the flame-spread direction. The flame spreading after two-droplet interaction in different directions is discussed considering the temperature distribution development. An approximation of the flame-spread-limit distance is also presented.