Experimental study on flame spread over wire insulation in microgravity

Abstract

An experimental study of flame spread phenomena over ETFE (ethylene-tetrafluoroethylene)-insulated wires has been performed in microgravity to obtain basic data on the fire safety of wire insulation. Three samples with different wire diameters, d w (0.32–0.51 mm) and the same insulation thickness, δ (0.15 mm) were investigated. The effects of the parameters thought dominant for wire combustion in fires: the ambient oxygen concentration, wire initial temperature, T i , wire diameter, d w , pressure, and dilution gas were investigated in the microgravity experiments. A series of comparative experiments were also conducted at normal gravity. The results show that flame spread rates in microgravity are higher than vertically downward spread rates at normal gravity when oxygen concentration is greater than 30% O 2 . However, with wire preheating, the spread rate in microgravity is higher than the downward spread rate at normal gravity even at lower O 2 concentrations. The increase in flame spread rates in microgravity became larger with decreases in d w . The effect of pressure on the flame spreading appeared very small, and lower pressure caused extinction of the flames in microgravity. The increase in flame spread rates in microgravity was especially large with CO 2 dilution, and this must be taken into account when selecting extinguisher gas. The microgravity experiments with CO 2 dilution gave rise to a new unsteady flame spread phenomenon for flame spreading over the wire: this phenomenon involves discontinuous flames partly occurring ahead of the spreading flame front.