Dominant Diffusion Flame Stabilized by Heat Source in Counter-Current Flow Between Two Plates

The premixed gas combustion in the planar channel with counter-current gas flow was experimentally and theoretically investigated. The gas combustion occurs in the presence of an external heat source located near the stagnant zone of the counter-current gas flow. Lean hydrogen–air mixtures with methane additives are used as a combustible mixture. It was shown that almost spherical sources of combustion resembling flame balls are formed near the stagnant zone at ultra-low flow velocities of the lean combustible mixture. With increasing gas velocity and enrichment of the combustible mixture, the flame repetitive extinction and ignition (FREI) regime was observed. The regimes diagram in the plane of gas flow stretch/gas mixture equivalence ratio was plotted. The novelty of this research is the experimental finding of ball-like flame structures similar to those typically observed only in microgravity conditions. The stable combustion of low‑hydrogen-concentrations mixtures in the form of separate flame balls is observed in the counter-current gas flow in the flat channel, with an external heat source located near the flow stagnation zone. The investigation of such combustion regimes can be interesting from both a fundamental point of view and for fire and explosion safety.