Microgravity experiments on droplet motionduring flame spreading along three-fuel-droplet array

摘要

Flame spreading along a fuel droplet array at microgravity has been studied as a simple model of spraycombustion. A three droplet array with a pendulum suspender was employed to investigate interactionsbetween flame spreading and droplet motion in the array direction. Initial droplet diameter was 0.8 mmand fuel was n-heptane. A silicon carbide pendulum suspender of 15 lm in diameter and 30 mm in lengthwas used for the third droplet. The first fixed droplet was ignited by electric spark. Behavior of the flameand the third droplet was observed using a high-speed video camera. Dimensionless span, which is the averageddroplet span divided by the averaged initial diameter of the three droplets, was varied from 2.7 to 10.Large displacement of the movable droplet was observed after group flame grew around the movable droplet.As the initial dimensionless span increased, the averaged droplet speed after the occurrence of flame spreadingto the movable droplet increased steeply, taking the maximum value around 5 in initial dimensionless span,and then decreased gradually. The movable droplet advanced toward the second droplet in small spans andmoved away from the second droplet in large spans. The direction of the motion changed around 4.6 in initialdimensionless span. Flame spread induction time from the second to the third droplet increased exponentiallyas the initial dimensionless span was increased. The induction time of flame spreading to a movable dropletwas longer than that of flame spreading to a fixed droplet. From calculations of flame spreading along a 20-droplet array, it was predicted that the droplet speed nearly converged after flame spread to the sixteenth droplet.The maximum speed of the nineteenth droplet appeared around 7.5 in the initial dimensionless span.