A field experiment of hydrogen-air deflagration

The behaviors of deflagrations initiated near the center of 1.5 m ³ hydrogen-air clouds were observed in a field experiment. The equivalence ratio of gas mixtures was varied in the range from 0.5 to 4.0. The corresponding changes of flame spread size, flame propagation velocity, and sound noise level were measured. In fuel lean cases, spherical flames were observed, while in fuel rich cases, the spherical flame propagation was followed by a rapid flame spread near the ground surface and a fireball at the top part of the cloud. The high-speed photographs and the records of ion probes show that the flame spread size and the flame acceleration increase with increasing the hydrogen concentration. The propagation velocity of spherical flames are one order of magnitude faster than the laminar burning velocity, and both quantities have a common dependency on the mixture equivalence ratio. The flame velocity reaches the maximum value of about 40 ms^-1 near the equivalence ratio of 2.0. The flame velocity in the fireballs reaches 180 ms^-1 at the maximum. The sound noise level increases with increasing equivalence ratio.