Experimental studies on dynamics of methane–air premixed flame in meso-scale diverging channels

The propagation characteristics of a laminar premixed flame front in meso-scale straight and diverging channels of 5°, 10° and 15° with inlet dimension of 25 mm × 2 mm are reported in this paper. The downstream part of the channels was heated with an external heat source, to maintain a positive wall temperature gradient along the direction of fluid flow. These investigations show that planar flames are observed near flash back limits. Negatively stretched flames were observed for moderate flow rates and rich mixtures and for high flow rates, flames were positively stretched. These flames were either symmetric or asymmetric in nature. Partially stable flames were observed at high velocities for rich mixtures, whereas for lean mixture partially stable flames were observed for all flow rates. All the divergent channels showed an improvement in high velocity limits compared with the straight channel for the same mixture. Planar flames observed in the experiments helped in determining the laminar burning velocities for these mixtures at different preheat temperatures. A co-relation of laminar burning velocity with mixture preheat temperature is also obtained for a stoichiometric methane–air mixture. This co-relation S_u/S_u,o = (T_u/T_u,o)^1.558 is in good agreement with the earlier co-relations.