抄録
In the hydrogen explosion at Fukushima Daiichi Nuclear Power Station, the presence of flammable organic compounds together with hydrogen in reactor buildings was suggested. Aiming to elucidate the explosion characteristics, we performed the experiments of spherically expanding hydrogen-methane-air lean premixed flames in a closed chamber, where methane was adopted as a representative of flammable organic compounds. At sufficiently small flame radii, smooth flame surface was observed. The addition of methane to hydrogen-air mixtures generated the increase in the propagation velocity of unstretched flame. At large flame radii, cellular surface induced by intrinsic instability was found, and the flame acceleration was confirmed. The parameters of flame acceleration model were estimated, and then the flame propagation velocity depending on the flame radius was predicted. The normalized increment coefficient became larger at low equivalence ratios, owing to stronger diffusive-thermal instability. Under the same hydrogen concentration, the methane addition generated the increase in the maximum pressure in a closed chamber. The maximum pressure of experiments was lower than that of calculations, which was because of heat loss during premixed combustion. Under the same methane concentration, the pressure ratio of experiments and calculations was lower when the flame propagation velocity was smaller. This was because of larger heat loss. The obtained results were valuable information to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station.
