An investigation of internal flame structure in porous media combustion via X-ray Computed Tomography

X-ray Computed Tomography (XCT) measurements are performed to characterize the internal volumetric flame structure within a Porous Media Burner (PMB). X-ray attenuation measurements are obtained using a multi-zone silicon carbide PMB combusting a radiodense Kr/O-2/N-2/CH4 mixture designed to enhance X-ray contrast. Time-averaged tomographic reconstructions of the X-ray attenuation field are used to assess internal PMB flame structure. Several key internal physical phenomena are observed, including heat recirculation within the combustion region, spatial inhomogeneity within the reaction zone, and preheating of gas in the upstream porous section. Further, the theory of XCT measurements applied to combustion systems is developed and implemented to arrive at 3D implied temperature field measurements at high spatial resolution. Implied temperature results are shown to exhibit quantitative agreement with those of a known 1D volume-averaged model for porous media combustion as well as with standard thermocouple measurements. These results shed light on internal thermophysical processes within PMBs while demonstrating the significant potential of XCT in obtaining quantitative, spatially resolved field data within optically inaccessible combustion environments. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.