Downward flame spreading over electric wire under various oxygen concentrations

Konno, Yuta; Hashimoto, Nozomu; Fujita, Osamu

doi:10.1016/j.proci.2018.05.074

Cited by 37 publications

(17 citation statements)

References 23 publications

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“…The abovementioned instabilities of flame spread in near-extinction conditions have not been previously reported in case of thin wires [16,18,19,21,24,25,43] and are considered to be a unique feature of thick insulation ones. In addition, the wire dimensions influenced the extinction mechanism of the flame spreading over the sample wires even in the same experimental conditions.…”

Section: Overall Characteristics Of Flame Spread and Extinction Under Normal Gravitymentioning

confidence: 85%

“…Electric wire combustion has the unique feature that the heat transfer through the metal conductor affects the fire performance of the insulation material during the burning event. Some researches on electric wire combustion under both normal gravity and microgravity have revealed that the role of the metal conductor in the flammability of the insulation material depends on the wire geometry [12][13][14][15] and surrounding ambient conditions such as O 2 concentration [16], airflow velocity [17][18][19][20], pressure [21], external radiative heat flux [15,22,23], and gravity [23][24][25][26]. Fujita et al [27][28][29] investigated the ignition limit and delay time of low-density polyethylene (LDPE)-insulated nichrome wires subject to short-and long-term excess electric current; they observed that the ignition limit dramatically expands in microgravity compared with normal gravity due to the absence of the buoyancy-induced flow.…”

Section: Introductionmentioning

confidence: 99%

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Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

et al. 2019

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Combustion of electric wires is the most probable cause of fire in human space activities. Therefore, the fire performance of electric wires in microgravity conditions must be thoroughly analyzed. This study investigates the opposed-flow flame spread and its limits in electric wires preheated by external radiation, under both normal gravity and microgravity, to understand their fire performance when exposed to external heat sources in such gravity conditions. The experiments were performed on low-density polyethylene (LDPE)-insulated copper (Cu) wires having an outer diameter of 4 mm and differing in core diameter (2.5 and 0.7 mm, corresponding to insulation thicknesses of 0.75 and 1.65 mm, respectively). Both standard and black LDPE insulations were used to study the effect of radiation absorption on the wire preheating and subsequent flame spread. The comparison of the flame spread limits revealed that the wire with the thicker Cu core was less flammable under both normal gravity and microgravity; in particular, its flammability further decreased in the case of microgravity, in contrast with thinner electric wires (~1 mm outer diameter), which exhibited higher flammability in the same gravity condition. These results suggest that different mechanisms, for thicker and thinner wires, determining the critical conditions to sustain flame spread under microgravity. This study provides valuable information about the fire performance of electric wires in space gravity.

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Section: Overall Characteristics Of Flame Spread and Extinction Under Normal Gravitymentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

et al. 2019

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“…Therefore, it is important to understand the ignition and flame spread behavior on wire insulation in microgravity, especially in the environmental conditions associated with spacecraft. Many of the important aspects related to the flammability of wire insulation in microgravity have already been studied for numerous materials and conditions; the ignition limit [4][5][6], the flame spread rate [7][8][9][10][11][12][13][14][15][16], and the extinction limit [17][18][19][20][21]. However, there are very few research results for flame spread over wire insulation in microgravity at various ambient pressure conditions.…”

Section: Introductionmentioning

confidence: 99%

Effect of ambient pressure on the extinction limit for opposed flame spread over an electrical wire in microgravity

Nagachi

Citerne

Dutilleul

et al. 2021

Proceedings of the Combustion Institute

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“…According to Takahashi et al [8], the most flammable condition of electrical wires do not exist in normal gravity, but rather in microgravity because of the reduction of buoyancy. Based on this fact, various aspects related to burning of wire insulation in microgravity have been studied, such as the ignition limit [9][10][11], flame spread rate [12][13][14][15][16][17][18][19][20][21], and extinction limit [8,22,23]. These studies have been carried out for numerous materials and under various conditions and have provided ample understanding of the physics of flammability characteristics of wires in microgravity.…”

Section: Introductionmentioning

confidence: 99%

Effect of Ignition Condition on the Extinction Limit for Opposed Flame Spread Over Electrical Wires in Microgravity

et al. 2019

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Flame spread over wire insulation plays a crucial role in spacecraft fire safety. To quantify the effect of the initial ignition condition on the Limiting Oxygen Concentration (LOC) of spreading flame over wire insulation, opposed flow flame spread experiments with wire insulation were conducted in microgravity (parabolic flights). Both ignition power (32.7 to 71.8 W) and heating time (5-15 s) were varied for an external flow of 100 mm/s. The sample wires were made of Polyethylene-coated Nickel-Chrome (NiCr) and Copper (Cu), respectively, both with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm. A 0.50 mm diameter coiled Kanthal wire wrapped around the sample wire 6 times with 8 mm length was used as the igniter. The experimental results show that the LOC gradually decreases as the ignition power or heating time increases and eventually it reaches a constant value. Also, the effect of ignition condition on LOC was more pronounced for Cu wires than for NiCr wires. The variation range of LOC in the tested ignition condition in microgravity was larger than that of horizontal flame spread in normal gravity. This conclusion can have implication for future experiment in the International Space Station to avoid the wrong LOC value because of the insufficient initial ignition energy and will eventually lead to an improved fire safety in spacecrafts.

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Downward flame spreading over electric wire under various oxygen concentrations

Cited by 37 publications

References 23 publications

Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

Effect of ambient pressure on the extinction limit for opposed flame spread over an electrical wire in microgravity

Effect of Ignition Condition on the Extinction Limit for Opposed Flame Spread Over Electrical Wires in Microgravity

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