**6. Concluding remarks of part 1**

In this monograph, combustion of solid carbon has been overviewed not only experimentally but also theoretically. In order to have a clear understanding, only the carbon combustion in the forward stagnation flowfield has been considered here. In the formulation, an aerothermochemical analysis has been conducted, based on the chemically reacting boundary layer, with considering the surface C-O2 and C-CO2 reactions and the gas-phase CO-O2 reaction. By virtue of the generalized species-enthalpy coupling functions, derived successfully, it has been demonstrated that there exists close coupling between the surface and gas-phase reactions that exerts influences on the combustion rate. Combustion response in the limiting situations has further been identified by using the generalized coupling functions.

After confirming the experimental fact that the combustion rate momentarily reduces upon ignition, because establishment of the CO-flame in the gas phase can change the dominant surface reaction from the faster C-O2 reaction to the slower C-CO2 reaction, focus has been put on the ignition of CO-flame over the burning carbon in the prescribed flowfield and theoretical studies have been conducted by using the generalized coupling functions. The asymptotic expansion method has been used to derive the explicit ignition criterion, from which in accordance with experimental results, it has been shown that ignition is facilitated with increasing surface temperature and oxidizer concentration, while suppressed with decreasing velocity gradient.

Then, attempts have been made to estimate kinetic parameters for the surface and gas-phase reactions, indispensable for predicting combustion behavior. In estimating the kinetic parameters for the surface reactions, use has been made of the reduced surface Damköhler number, evaluated by the combustion rate measured in experiments. In estimating the kinetic parameters for the global gas-phase reaction, prior to the appearance of the COflame, use has been made of the ignition criterion theoretically obtained, by evaluating it at the ignition surface-temperature experimentally determined. Experimental comparisons have also been conducted and a fair degree of agreement has been demonstrated between experimental and theoretical results.

Further studies are intended to be made in Part 2 for exploring carbon combustion at high velocity gradients and/or in the High-Temperature Air Combustion, in which effects of water-vapor in the oxidizing-gas are also to be taken into account.
