Effect of Flow Direction on the Extinction Limit for Flame Spread over Wire Insulation in Microgravity

Abstract

Experiments to determine the Limiting Oxygen Concentration (LOC) of a flame spreading over electric wire insulation were carried out in microgravity (parabolic flights) and in normal gravity, and the difference between the LOC in opposed and concurrent flows was evidenced under microgravity (μG). Polyethylene insulated Copper (Cu) wires and polyethylene insulated Nickel-Chrome (NiCr) wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were examined with external flow velocities ranging from 50mm/s to 200mm/s. The results for Copper wires show that with increasing external flow velocity, the LOC monotonically decreased in concurrent flow condition and the LOC first decreased and then increased (“U” trend) in opposed flow condition. These trends were similar to the results of the experiments with NiCr wires. Also, in terms of the minimum LOC value (MLOC), the MLOC for concurrent flow was about 1-2% lower in Oxygen concentration than that for opposed flow in both wires cases. Further, when comparing the MLOC of NiCr wires with the MLOC of Cu wires, it was found that the MLOC of the NiCr wires was close to that of Cu wires for concurrent flow conditions. However, the MLOC of the NiCr wires was about 1% lower in Oxygen concentration than that of Cu wires for opposed flow conditions. These results provide insight into the mechanism of extinction limit of flame spread over wire insulation, especially the effect of flow direction and core wire material, both of which will be useful for improving fire safety onboard spacecraft.

Description

Masashi Nagachi, Hokkaido University, Japan
Fumiya Mitsui, Hokkaido University, Japan
Jean-Marie Citerne, Université Pierre et Marie Currie, France
Hugo Dutilleul, Université Pierre et Marie Currie, France
Augustin Guibaud, Université Pierre et Marie Currie, France
Grunde Jomaas, University of Edinburgh, United Kingdom
Guillaume Legros, Université Pierre et Marie Currie, France
Nozomu Hashimoto, Hokkaido University, Japan
Osamu Fujita, Hokkaido University, Japan
ICES509: Fire Safety in Spacecraft and Enclosed Habitats
The 47th International Conference on Environmental Systems was held in South Carolina, USA on 16 July 2017 through 20 July 2017.

Keywords

Microgravity, Flame spread, Opposed flow, Concurrent flow, Polyethylene insulated wire, Limiting Oxygen Concentration

Citation