Flame acceleration in rough narrow channels

Abstract

Flame acceleration in rough narrow channel was experimentally studied for the mixtures of hydrogen with air and acetylene with air. The experiments were carried out in a 7 by 7 mm smooth channel or a channel with one or two opposite walls covered with sandpaper which had a grain size of 100 μm or 500 μm. Using high-speed schlieren and self-luminance visualization several flame acceleration regimes were discovered depending on the channel roughness and composition of the combustible mixture. In all cases, the highest maximum flame velocity was observed in rough channels. Detonation was also obtained only in the rough channels, despite the smaller effective channel size when using sandpaper. It was found that the maximum flame velocity and DDT distance depended non-linearly on the channel blockage ratio (BR). The highest flame velocity and the shortest transition to detonation were recorded at BR of 0.035. At highest BR of 0.16, detonation was not recorded in any of the combustible mixtures used. Using schlieren diagnostics, it was discovered that disturbances of the unburned mixture occur above the rough surface, which lead to an increase in pressure ahead of the flame front. The occurrence of detonation was also detected near the rough surface.