Combustion rates of graphite rods in the forward stagnation field with high-temperature airflow

Abstract

An experiment has been conducted to measure combustion rates of graphite rods in the forward stagnation field with high-temperature airflow of 1280 K, to elucidate its combustion behavior. It is found that the combustion rate in the high-temperature airflow is enhanced, because of the elevated transport property due to an increase in the airflow temperature, when the mass flow rate of air is kept constant, and that it is reduced, because of a reduced mass transfer rate of oxygen through the thickened boundary layer, due to reduced density in the gas phase, when the velocity gradient is the same. It is also confirmed that even in the high-temperature air combustion, there occurs an abrupt decrease in the combustion rate when the velocity gradient is lower than about 1000 s −1, because of the establishment of the CO flame. Theoretical works have also been conducted and it is found that the combustion rate can fairly be obtained numerically, as far as the trend and the approximate magnitude are concerned. It has turned out that the combustion rate in the high-temperature oxidizer-flow has nearly the same value as that in the room-temperature airflow even when the oxygen mass fraction is reduced to be about 0.15. It is also found that the oxygen mass fraction can be reduced to be about 0.07, when there exists enough CO 2 in the oxidizer and the surface temperature is enough high, say, more than 2000 K.