Flame structure and combustion rate of burning graphite in the stagnation flow

Abstract

The combustion behavior of graphite rods in the stagnation flow of an oxidizer is studied experimentally to investigate the coupled nature caused by the interaction between the gas-phase and surface reactions. Toward this aim, not only the combustion rate but also the gas-phase temperature profile is measured as a function of the surface temperature of the burning graphite. The temperature profile over the burning graphite rod is measured with CARS thermometry. It is observed that with increasing surface temperature, the temperature profile in the gas phase shifts from that without CO flame to that with CO flame. At the ignition surface temperature, at which a CO flame is established in the forward region, it is observed that there exists a reaction zone whose temperature is nearly equal to the surface temperature. When the surface temperature is higher than the ignition surface temperature, a reaction zone whose temperature is higher than the surface temperature is observed. It is confirmed that the abrupt reduction in the combustion rate is related closely to the change of the flame structure in the gas phase caused by the establishment of the CO flame in the forward stagnation region, by which the dominant surface reaction changes from the C-O 2 reaction to the C-CO 2 reaction. Experimental results are also compared with predicted results with the gas-phase and surface kinetic parameters reported in the literature. A fair degree of agreement is demonstrated as far as the trend and approximate magnitude are concerned.