Flame acceleration and detonation initiation process over porous flat wall

Abstract

The flame acceleration process and detonation initiation process of the ethylene and oxygen-rich air mixture over porous flat wall are experimentally studied using high-speed photography technology. The results show that there are two flame acceleration modes over porous flat wall with four pore densities. The flame acceleration over porous flat wall with small pore density (10ppi and 30ppi) is driven by the high velocity flame inside the porous media. Regarding the porous flat wall with larger pore density (40ppi and 50ppi), the flame undergoes an initial acceleration process inside the porous media, following by the further acceleration due to the joint effects of rough wall disturbance and mainstream in the detonation tube. The distance for laminar flame to accelerate to 0.5CJ (Chapman-Jouguet) velocity is 55 mm and 100 mm over porous flat walls with small pore density and large pore density, respectively. To reveal the detail acceleration magnitude of the flame in the porous media, different porous media obstacles are set in the tube. The laminar flame accelerates to a maximum velocity of approximately 300 m/s in large pore density porous obstacles. While in smaller pore density porous obstacles, the maximum flame velocity is much higher. Regarding the detonation initiation, it is found to be triggered by the local explosion generated by the action of shock wave over porous flat wall with four pore densities. The smaller the pore density is, the closer the position of the local explosion is to the upstream detonation tube.