Experimental Study on the Combustion Characteristics of Polyurethane Under High Pressure and Low Oxygen Environment

Abstract

Closing the coal mine and injecting nitrogen, as a common fire fighting method, will form a high pressure and low oxygen environment in the closed coal mine. To investigate the fire risk of the rigid polyurethane (PU) foam under this environment, a series of experiments were carried out in the self-designed device. In the experiments, the oxygen concentration (pressure) changed from ${21}\%\, ({0.101}\,{\hbox {MPa}})$ to ${16}\,{\%}\, ({0.133}\,{\hbox {MPa}})$, and the material thickness varied between ${3}\,{\hbox {cm}}, {4}\,{\hbox {cm}}$ and ${5}\,{\hbox {cm}}$. PU’s flame speed, flame height and gas-phase temperature were obtained and analyzed from different aspects. The experimental results are as follows: (1) The effect of oxygen concentration reduction was stronger than that of pressure increase on flame speed. The critical heat flux of vertical flame propagation and the volume of carbon skeleton structure, which were influenced by the material thickness, affected the flame speed. (2) Under the influence of oxygen concentration and buoyancy of mixed gas in closed area, the normalized flame height showed a unique variation rule. (3) The final absolute pressure in the experimental equipment could be compared with the initial pressure to show the insufficiency of combustion. The maximum gas-phase temperature at ${3}\,{\hbox {cm}}$ above the fuel surface showed different variation patterns, when the average optical density of soot particles were on the two sides with 200 (dimensionless number). The results illustrate that in the high pressure and low oxygen environment, reducing the oxygen concentration rapidly is the key to extinguishing the coal mine fire, although the increase in pressure will enhance the intensity of combustion.