Quasi-steady and transient combustion of a carbon particle: Theory and experimental comparisons

The combustion of a carbon particle in an O₂/CO₂/Inert environment is theoretically studied for the quasi-steady situation of constant particle temperature and the transient situation with particle heating and radiative heat transfer. Chemical reactions considered include the surface C-O₂ and C-CO₂ reactions and the gas-phase CO-O₂ reaction. Generalized species-enthalpy coupling functions are derived for this chemically-complex system without assuming any limit or near-limit behavior, thereby providing useful insight into the appropriate conserved quantities in carbon combustion as well as facilitating further theoretical developments. Calculated results emphasize the intimate coupling between the gas-phase and surface reactions, the importance of radiative heat loss, and the fact that the particle combustion mechanism is intermediate of those assuming frozen and equilibrium gas-phase reactions. By using a restrictive set of kinetic and thermophysical parameters, it is further demonstrated that the theoretical calculations agree well with existing experimental data for both the quasi-steady and transient combustion situations.