The role of radical wall quenching in flame stability and wall heat flux: hydrogen-air mixtures

Abstract

The role of wall quenching of radicals in ignition, extinction and autothermal behaviour of premixed H₂–air flames impinging on a flat surface was studied using numerical bifurcation techniques, with detailed gas-phase chemistry and surface radical recombination reactions. Quenching out of radicals was found to retard the system at ignition due solely to the kinetics of the surface reactions. While kinetically extinction is also retarded, the thermal feedback from the wall recombination of radicals can render the flame more stable and lead to a higher wall heat flux as a function of wall temperature compared to an inert surface under some conditions. It is also shown that the combined kinetic and thermal effects of wall radical quenching can expand the autothermal regime. Implications for estimating flammability limits near reactive surfaces of tubes are finally discussed.

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