Flame spread experiments with wire insulation were conducted in microgravity (parabolic flights) and in normal gravity to understand the effect of the ignition condition on the Limiting Oxygen Concentration (LOC) for an opposed air flow condition of 100 mm/s (typical flow velocity on ISS). Both the ignition power (50-110 W) and the igniter heating time (5-15 s) were varied. Polyethylene-coated Nickel-Chrome or copper 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 the igniter. The experimental results show that the LOC of NiCr core wires assume 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 more evident in microgravity than in normal gravity. The variation in LOC value is about 2% within the tested range of ignition conditions. 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. In Cu core wire cases, the LOC monotonically decreases as the heating time increases because of preheating by the igniter. This preheating helps to sustain spreading during microgravity period. Future study is required to find the proper ignition condition for a high-conductivity wire. The results have the potential to improve safety aspects associated with the development of a fire safety standard for spacecraft.
|Number of pages||5|
|Publication status||Published - 2017|
|Event||47th International Conference on Environmental Systems - Charleston, United States|
Duration: 16 Jul 2017 → 20 Jul 2017
Conference number: 47
|Conference||47th International Conference on Environmental Systems|
|Period||16/07/2017 → 20/07/2017|