Influence of a heat-absorbing surface on the propagation of a hemispherical flame

Abstract

Gaseous explosions lead to severe damage. Elimination or mitigation of damage is a key problem in industrial safety. This paper presents an experimental study of hydrogen–air flame front dynamics and flame suppression by means of a surface coating. The experimental stand is a metal frame that confines the cylindrical envelope to a diameter of 1.5 m and 2.4 m in height of high-density 100 μm thick polyethylene. Experimental data on the hemispherical flame propagation in hydrogen–air mixtures with a hydrogen content of 15% were obtained at the initiation of combustion with an energy of 5 J. The flame propagates at atmospheric pressure over a solid aluminium wall or a layer of steel wool. To measure the flame propagation speed, an infrared InfraTec ImageIR 8320 camera with spectral range 2–5.7 μm was used. The flame acceleration dynamics were compared at flame radii up to 0.4 m. It was found that in a mixture with a hydrogen content of 15% the flame over the layer of steel wool propagates 2.5 times more slowly than that over the surface of an aluminium wall. The steel wool was investigated by scanning electron microscope using an energy dispersive analysis system before and after the passing of the flame front. The structure and chemical composition of the metal wool was studied. Calculation of heat absorption in the steel wool layer shows that the heat losses due to the absorption are the main phenomenon causing the flame front speed reduction, which was observed in the experiments. Additionally, the speed of the flame was affected by the absorption of oxygen and the release of heat during the oxidation of the steel wool, as well as by the roughness of the layer of steel wool.