Browsing by Author "Dutilleul, Hugo"
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Item Effect of Flow Direction on the Extinction Limit for Flame Spread over Wire Insulation in Microgravity(47th International Conference on Environmental Systems, 2017-07-16) Nagachi, Masashi; Mitsui, Fumiya; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments 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.Item Effect of flow direction on the extinction limit of spreading flame over wire insulation(46th International Conference on Environmental Systems, 2016-07-10) Nagachi, Masashi; Mitsui, Fumiya; Kizawa, Koki; Citerne, Jean-Marie; Dutilleul, Hugo; Jomaas, Grunde; Legros, Guillaume; Fujita, OsamuFire safety is one of the most important issues for manned space mission, because a fire in a spacecraft may results in irreversible alteration of the crew's environment. Electric wire is a major cause of fire accidents in spacecraft. So, it is very important to study the flammability of electric wire under microgravity conditions. In this paper experimental works to determine Limiting Oxygen Concentration (LOC) of spreading flame over electric wire insulation have been carried out and the difference between the LOC in opposed and concurrent flows has been evidenced under both normal gravity (1G) and microgravity (μG). Polyethylene (PE) insulated Nickel-Chrome (NiCr) wires with inner core diameter (dc) of 0.50 mm and insulation thickness (dp) of 0.30 mm are examined with external flow velocity ranging from 50mm/s to 200mm/s. Microgravity environment is provided along parabolic flights onboard the French A310 airplane. Results show that with increasing external flow velocity, the LOC in 1G first decreases and then increases (“U” trend) for both of opposed and concurrent cases. On the opposite the LOC in μG monotonically decreases with increasing external flow velocity. Furthermore the LOC in μG is lower than that at 1G because natural convection is vanished. Comparing opposed and concurrent flows in 1G condition, the LOC tendencies following the modification of the flow velocity are very similar and the minimum value is almost the same. On the other hand, in μG condition, the LOC value is almost the same within the low flow velocity region for both flow directions, but the LOC for concurrent flow is about 2% smaller in Oxygen concentration than that for opposed flow within the high flow velocity region. This research is supported by Japan Space Exploration Agency (JAXA) under the project of FLARE and the Centre National d'Etudes Spatiales (CNES) under contract #130615.Item Effect of the Ignition Method on the Extinction Limit for a Flame Spreading over Electric Wire Insulation(47th International Conference on Environmental Systems, 2017-07-16) Mitsui, Fumiya; Nagachi, Masashi; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments for flame spreading over electric wire insulation were conducted in parabolic flights (microgravity) and on ground (normal gravity) to understand the effect of the ignition condition on the Limiting Oxygen Concentration (LOC) for electric wires under an external, opposed flow condition of 100 mm/s (typical flow velocity on ISS). Both the ignition power and the igniter heating time were varied ranging from 50 W to 110W and from 5 s to 15 s in order to investigate the ignition condition effect. Polyethylene-coated Nickel-Chrome wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were used as sample wires, and a 0.50 mm diameter coiled Kanthal wire was used as igniter. The experimental results show that the LOC assumes an almost constant value under normal gravity conditions once ignition occurred, whereas under microgravity conditions, the LOC gradually decreases as the ignition power or heating time increases and eventually it reaches an almost constant value. Thus, the effect of ignition condition on LOC is stronger in microgravity than in normal gravity. The difference in oxygen concentration between the maximum and the minimum LOC was about 2% within the tested range of ignition conditions. This means that additional heating is required after ignition occurs to obtain the correct LOC. Finally, the results suggest that there exists a minimum ignition power and heating time to obtain the correct LOC values for electric wire combustion, especially in microgravity. This result has the potential to improve safety aspects associated with the development of a fire safety standard for spacecrafts, and consequentially also to improve spacecraft fire safety in general.