Effect of channel geometry and porous coverage on flame acceleration in hydrogen–air mixture

Abstract

Flame propagation in a hydrogen–air mixture in the presence of porous materials was investigated experimentally in channels with different dimensions and cross–sections. In this study, experiments were performed in a rectangular channel with one or two walls covered with porous material to study flame propagation in stoichiometric hydrogen–air mixtures at room temperature and atmospheric pressure. Depending on the channel configuration, the porous coating of the internal walls ranged from 1/4 to 1/2 of the channel area. Four types of polyurethane foam with a number of pores per inch (PPI) ranging from 10 to 80 were used to cover the channel walls. Flame propagation was visualized using a Schlieren device and high-speed camera. The largest flame acceleration in the porous channel relative to the solid channel was observed in the 20×20mm channel. The ratio of the velocities in the porous channel to the velocity in the solid channels was 6–7 for the porous material with the largest (2.5mm) pores. In the case of a 10×10mm channel, the flame velocity in the porous channel was higher than the flame velocity in the solid channel after 350mm only when using porous coatings with 2.5mm and 1.3mm pores. When using a porous coating with smaller pores the flame velocity was lower than in the solid channel. Schlieren images show different stages of flame propagation from a turbulent flame to a supersonic flame with shock waves.