UB-FIRE Experiment Results on Upward Flame Propagation along Cylindrical PMMA Samples in Reduced Gravity

Aiming for improvements on fire safety in human spaceflight, upward flame propagation is examined on three different cylindrical PMMA rods during the REXUS 20 sounding rocket mission within the UB-FIRE project. The rods are of identical diameter of 15 mm with a reference sample of a smooth surface, one sample featuring vertical grooves and one sample exhibiting two vertical ribs. The concurrent flow of air is identical for all three samples with 18 cm/s velocity which is comparable to air conditioning flow velocities in space habitats like the International Space Station. The advantage of the cylindrical shape is that no border effects occur. The leading edge of the pyrolysis front is observed by means of an infrared camera centrally mounted between the surrounding wind tunnels alternately looking to the individual samples. The UB-FIRE experiment, flown on REXUS 20 in a reduced gravity environment (~0.094 g), reveals a reduced pyrolysis front propagation velocity up to a factor of 0.28 compared to ground-based experiments with an identical test setup (NASA-STD-6001B test 1). However, the corrugation effect which affects the propagation velocity is different in a reduced gravity environment compared to 1g. Possible reasons for this behavior along with a detailed evaluation of each sample are discussed in this paper. The 1g results are used to develop and validate an empirical model for the flame propagation along structured surfaces of several shapes.