2016 Volume 58 Issue 184 Pages 107-113
To understand the high-pressure premixed combustion mechanism in a meso-scale packed porous bed, crosssectional visualization of propagating flames in a packed bed was performed at high pressure up to 1.0 MPa. For easy optical access to the interior, a two-dimensional pseudo packed bed combustor was developed, which has quartz-glass cylinders installed in a rectangular duct representing the network of meso-scale flow channels of the bed. Visualization of propagating flames in the 2-D packed bed was performed using both a visible-light high-speed photography and Planar Laser Induced Fluorescence (PLIF) method targeting OH radicals. Fast flame propagation through the 2-D packed bed with a broad chemiluminescence region was observed at high pressure, characteristics of which was presumed to be identical to the fast flame propagation in the packed bed of spheres in authors' previous research. Instantaneous cross-sectional visualization with OH-PLIF was subsequently conducted. Obtained PLIF images as well as the result of turbulence measurement in the 2-D packed bed showed that turbulent flames with concave and convex cusps can be formed even in meso-scale flow channels at high pressure, resulting in a high flame displacement speed. The mechanism of the turbulent flame formation in quite a narrow flow channel was subsequently explained by comparison among characteristic scales of turbulence, hydrodynamic flame instability combined with diffusive-thermal effect, and flow channels. OH-PLIF images also revealed the existence of multiple propagating flame fronts inside the broad chemiluminescence region, in which the leading flame front was presumed to be predominant on the flame propagation in the packed bed.
