Combustion in a horizontal channel partially filled with porous media

Summary

Experiments were carried out to investigate the combustion phenomenon in a horizontal channel partially filled with 12.7 mm diameter ceramic oxide beads. A 1.22 m long, nominally 45 mm thick layer of ceramic oxide beads is located at the ignition end of a 2.44 m long, 76 mm square channel. The channel is filled with a 31 percent nitrogen diluted stoichiometric methane-oxygen mixture and an automotive spark ignition system is used to ignite a flame at the end of the channel. Instrumentation includes ionization probes and piezoelectric pressure transducers. High-speed Schlieren video was used to capture the structure of the explosion front. Experiments were performed at room temperature and at an initial pressure in the range of 14 kPa to 50 kPa. At low initial pressures, a mode of combustion was observed where the reaction in the gap above the bead layer dominates the combustion within the porous media. As the initial pressure of the mixture was increased, combustion within the porous media became more dominant and began to drive the combustion in the gap above the layer. Pressure tme-history and flame time-of-arrival data indicate that transition to detonation occurs within the bead layer section of the channel for mixtures at an initial pressure of 30 kPa and higher. As the initial pressure is increased, transition to detonation occurs closer to the ignition source in the gap above the bead layer.