A comprehensive study of two interactive parallel premixed methane flames on lean combustion

This study aims to investigate interactive parallel lean premixed methane flames issued from twin rectangular slot burners with variable jet spacing, equivalence ratios and inlet speeds. The flowfield and combustion chemical reactions are predicted by detailed numerical simulation with Skeletal and GRI-v3.0 mechanisms. Numerical results such as velocity streamlines, temperature, flame height and flame shape are validated with those obtained by experimental particle image velocimetry (PIV) and flame measurements. When moved closer beyond a threshold jet spacing, these twin flames become interactive and both flames tilt outward in appearance with a wider operational range of lean and velocity conditions. Numerical predictions of flowfields found that there are three different interacting stages: entrainment, recirculation and reverse flows according to jet-to-jet spacing and they are named by their characteristic postflame flowfields between jet burners. At the reverse flow stage, a stagnating flowfield termed lateral impingement is generated along the symmetric axis between the flames, which is similar but not identical to that found in the counter-flow flames. As the jet spacing is reduced, the flowfield transition of the interacting postflame stages is believed to be the main mechanism to enhance the flame stabilization, especially in lean conditions. This reverse flow pattern provides a hot and slow postflame flowfield and transports the residual OH radicals from the main flames to heat and burn the fuel escaping from the stand-off gap between the flame base and burner rim through low temperature burning process. In other words, the stabilization of the interactive twin flames is enhanced by a number of crucial factors such as lateral stagnating flow, low dissipation of thermal and interacting chemical species supplied from the main flames.