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

Abstract

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.

Pressure effects on the soot production and radiative heat transfer of non-buoyant laminar diffusion flames spreading in opposed flow over insulated wires

“…First, it corresponds to an international target configuration to investigate fundamentally the flammability properties of electrical wires. Their use has emerged with the work of Bakham et al [28] and, over the last twenty years, a significant amount of experimental studies, mainly related to fire safety in spacecraft, have adopted the PE coated wire configuration [3], [4], [29]- [34]. Second, it produces soot volume fraction levels above the detection threshold of the BMAE over the range of pressure considered in the present study.…”

Broadband modulated absorption/emission technique to probe sooting flames: Implementation, validation, and limitations

“…In the absence of buoyancy forces, most fire detection and control apparatuses developed on earth are inefficient [2] . To get a better understanding of the risks, flame spread rate over solid samples in microgravity has been studied by various methods such as flame front or solid-phase temperature tracking [3,4] . Ongoing unique experiments over large flat samples aim at the fine characterization of fire spread over solid samples [5] .…”

Introduction to Special Issue on Spacecraft Fire Safety

“…Unique space fire experiments have been conducted in the International Space Station [5,6], unmanned spacecraft [7], and a satellite [8] to understand the long-term micro-gravity combustion and fire phenomena. The fire dynamics small and thin fuels are also explored through ground-based microgravity experiments using drop towers [9] and parabolic flights [10][11][12][13][14]. In addition, combustion and fire experiments under reduced pressures [15][16][17] and a narrow channel [18] are applied to lower the influence of buoyancy and simulate low-gravity environments on Earth.…”

“…Proper material selection for spaceflight requires a thorough knowledge of fire and flammability behavior in varied gravity. Thus, the critical conditions for flame ignition and extinction in microgravity are extensively explored under different ignition protocols [12], oxygen concentrations [11][12][13], airflow rates [13] and radiant heat fluxes [11], and for flame retardant materials [13].…”

“…Thus, microgravity also provides an ideal environment for fundamental combustion research [4]. Unique phenomena for flame spread in microgravity over thin paper [9], thick plastic plates [7,10,18], cylindrical rods [8,17], spherical fuels [5] and electrical wires of different thicknesses [11,12,14,20] are observed, and the influence of airflow speed, direction, and oxygen concentration on flame stability are investigated.…”