Expanding hydrogen–air flames over the heat absorbing substrate

Abstract

Acceleration of hemispherical gas flames depends both on the composition of the gas mixture and on the boundary conditions. Experimental data on the hemispherical flame propagation in hydrogen–air mixtures with a hydrogen content of 15% were obtained at the ignition with an energy of 5 J. The flame propagates at atmospheric pressure over a solid aluminium wall or a layer of steel wool. To visualize the flame propagation, an ir InfraTec ImageIR 8320 camera with spectral range 2–5.7 µm was used. It was found that the flame over the layer of steel wool propagates 1.8 to 2.5 times more slowly than that over the surface of an aluminium wall. 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.