Scalar Measurements in Bluff Body Stabilized Flames Using Cars Diagnostics

Abstract

Measurements of mean and rms temperature fluctuations were performed in confined turbulent premixed methane-air flames, stabilized on a conical flameholder. A CARS system was used for these measurements. These tests employed flameholders of different blockage ratios (13% and 25%), and mixtures with different equivalence ratios (0.56, 0.65, 0.8, and 0.9) and approach turbulence intensity (2%, 17%, and 22%). It was found that the recirculation zone closely resembles a perfectly well-stirred reactor. Blockage ratio, equivalence ratio, or approach turbulence intensity did not alter the scalar field. The turbulent flame structure enveloping the recirculation zone comprises: (i) an ignition/thin flame region in the vicinity of the flameholder base, (ii) a reacting shear layer region of large-scale coherent structures, and (iii) a thick flame region where entrainment is the dominant mechanism. Finally, analysis suggests that the scalar gradient-diffusion relationship is valid and areas of non-gradient diffusion, if any, are probably small.