Investigation of flame spread over a thin wire under simulated lunar and terrestrial gravity using a centrifuge during parabolic flight

This study investigates the flame spread behavior of thin wires under simulated lunar (0.166 G) and terrestrial (1 G) gravity conditions using a centrifuge aboard a parabolic flight platform. Experiments were conducted under both uniform gravity and artificial gravity generated by centrifugal acceleration. The effects of gravity on flame spread were examined through flame shape observation, pressure measurement, flow visualization, motion analysis of induced convection, and flammability limit evaluation. Results demonstrated that the flammable range of the specimens expands under artificial gravity compared to uniform gravity. Flow visualization revealed the formation of a swirling convective flow around the axis of rotation, driven by the combined effects of centrifugal and Coriolis forces. This recirculating flow increased chamber gas temperature by reducing the cooling effects of internal structures, resulting in a 4–6 kPa higher pressure rise during flame spread. Motion analysis indicated that convection under artificial gravity exhibits quasi-steady rotational behavior, which suppresses overall convective strength. These findings suggest that simply matching the centrifugal force at the specimen location is insufficient for quantitatively reproducing extinction behavior observed under uniform gravity. To achieve comparable flammability limits, a centrifugal force exceeding 1.5 times the equivalent gravitational acceleration is required under the present setup. The dynamics of swirling recirculating flow play a critical role in determining flame behavior in artificial gravity environments.