Combustion Regimes of Ultralean Methane–Hydrogen/Air Premixed Flames with Dominant Diffusion Transport Process

The combustion regimes of ultralean premixed methane–hydrogen–air flames were experimentally investigated in the planar channel with counterflow gas supply in the presence of local heat source in stagnant zone. It was shown that at low flow velocities of a lean combustible mixture, almost spherical, ball-like flames are formed near the stagnation zone. With increasing gas velocity and enrichment of the mixture the flame repetitive extinction and ignition regime (FREI regime) was observed. The local gas flow velocity near twin spherical sources of combustion was estimated. The average radius of single ball-like sources of combustion was measured for different mixture contents and inlet mixture velocities. The regime diagram of ball-like flame formation, FREI regime and flammability limit was plotted.