A narrow channel experimental study on flammability characteristics of thermally thin fuels under simulated microgravity conditions

The flame spread over thermally thin solid material surfaces and the flammability limits of such material have been experimentally investigated in narrow channels with height of 10 mm, 12 mm and 14 mm, which are used to produce simulated microgravity conditions in laboratory. The experimental results under conditions of flow velocity of 0-50 cm/s and oxygen concentration of 18% and 21% are compared with those from previous tests conducted under the microgravity condition. For flow velocities less than 15-20 cm/s, flame spread characteristics under microgravity condition can be effectively reproduced in narrow channels of 12 mm and 14 mm height, moreover, for flow velocities greater than 15-20 cm/s, flame spread rates under the microgravity can well be simulated by flames spreading in the 10-mm-height channel. In narrow channels with height of 12 mm and 14 mm, the measured flammability map is found close to that obtained at microgravity, whereas the flammability boundary obtained in the 10-mm-height channel deviate from the microgravity case. The experiments show that the buoyant convection is suppressed to a great degree in narrow channels, consequently in which a simulated microgravity environment can be produced. The results also indicate some quantitative differences between observations under simulated and actual microgravity conditions, and these diversities in quantities may be attributed to the effects of residual buoyant convection in narrow channels and heat loss on channel walls.