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Carbon combustion has been a research subject, relevant to pulverized coal combustion. However, it is not limited to basic research on coal/char combustion, but can benefit various aerospace applications, such as propulsion due to its high energy density and evaluation of protection properties of carbon-carbon composites (C/C-composites) used as hightemperature, structural materials for atmospheric re-entry, gas-turbine blades, scram jet combustors, etc., including ablative carbon heat-shields. Because of practical importance, extensive research has been conducted experimentally, theoretically, and/or numerically, as summarized in several comprehensive reviews (Batchelder, et al., 1953; Gerstein & Coffin, 1956; Walker, et al., 1959; Clark, et al., 1962; Khitrin, 1962; Mulcahy & Smith, 1969; Maahs, 1971; Rosner, 1972; Essenhigh, 1976, 1981; Annamalai & Ryan, 1993; Annamalai, et al., 1994). Nonetheless, because of complexities involved, further studies are required to understand basic nature of the combustion. Some of them also command fundamental interest, because of simultaneous existence of surface and gas-phase reactions, interacting each other. Generally speaking, processes governing the carbon combustion are as follows: (i) diffusion of oxidizing species to the solid surface, (ii) adsorption of molecules onto active sites on the surface, (iii) formation of products from adsorbed molecules on the surface, (iv) desorption of solid oxides into the gas phase, and (v) migration of gaseous products through the boundary layer into the freestream. Since these steps occur in series, the slowest of them determines the combustion rate and it is usual that steps (ii) and (iv) are extremely fast. When the surface temperature is low, step (iii) is known to be much slower than steps (i) or (v). The combustion rate, which is also called as the mass burning rate, defined as mass transferred in unit area and time, is then determined by chemical kinetics and therefore the process is kinetically controlled. In this kinetically controlled regime, the combustion rate only depends on the surface temperature, exponentially. Since the process of diffusion, being conducted through the boundary layer, is irrelevant in this regime, the combustion rate is independent of its thickness. Concentrations of oxidizing species at the reacting surface are not too different from those in the freestream. In addition, since solid carbon is more or less porous, in general, combustion proceeds throughout the sample specimen.

Mass Transfer Related to Heterogeneous Combustion of Solid Carbon in the Forward Stagnation Region - Part 1 - Combustion Rate and Flame Structure