The study of geometric effects on the explosion front propagation in a horizontal channel with a layer of spherical beads

Experiments were performed in a horizontal channel partially filled with a layer of 12.7 mm ceramic-oxide beads filled with a nitrogen-diluted stoichiometric methane–oxygen mixture, i.e., CH_4 + 2(O_2 + 2/3N_2). Ionization probes and pressure transducers were used to track the explosion front velocity in the 1.22 m long, 76 mm wide and 152 mm high horizontal channel. Schlieren photography and smoked foil techniques are used to gain insight into the explosion front structure. The explosion propagation phenomenon was characterized by the combustion in the bead layer and the unobstructed gap above. It was determined that for a fixed gap height the bead layer thickness had very little effect on the explosion propagation phenomenon. However, for a fixed bead layer height the explosion propagation was strongly influenced by the gap height. The combustion products vented from the bead layer behind the flame propagating in the gap affects the structure of the shock-flame front in the gap and the maximum flame velocity achieved. The coupling between the vented products and the flame velocity in the gap was strongly influenced by the gap height. The gap height also affects the structure of the detonation wave propagating in the gap following DDT that always occurred in the gap. The DDT run-up distance was found to increase with increasing gap height and inversely with initial pressure.