The oxidation of graphite powder in flame reaction zones

The rate of burning of small concentrations of fine graphite powder has been measured in a flat, laminar weak methane-air flame at sub-atmospheric pressure. Measurements were obtained with a laser doppler system, that not only measured particle velocities, but also particle concentrations and size distributions through the flame. Particle temperatures were measured by the two colour method and gas temperatures with thermocouples. An appreciable increase in the oxidation rate was observed in the flame reaction zone, attributable to the reaction zone transient species, O, H, and OH. A computational study of the flame, with comprehensive chemical kinetics and detailed representation of the transport fluxes, yielded the concentrations of all species through the flame. The observed rates of graphite oxidation are kinetically explained in terms of rates of reaction of all species with graphite. The observed elevations of particle above gas temperature in the reaction zone are higher than would be expected if the heating were due only to reactions in which the carbon surface was attacked. Amongst other possible explanations there is that of heating by exothermic radical recombination on the carbon surface.

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