Effect of radiative heat feedback on burning rate of metalized propellants

Metalized solid propellants have higher final flame temperatures and higher flame radiant intensities than non-metalized propellants. However, the importance of radiative heat feedback in metalized propellant combustion is still relatively unknown. In this study, radiative effects in metalized propellants containing aluminum, boron, and magnesium were examined by embedding optical fibers and micro-thermocouples in propellants to measure radiative and conductive feedback, respectively. Extinguishment by rapid depressurization was used to determine the condition and location of the thermocouple and optical fiber at the burning surface. Hemispherical reflectivity measurements were also made to determine propellant absorptivity. The reflectivity measurements showed that even a small amount of a metal powder in a propellant increases the absorptivity significantly. In the metalized propellants, radiative heat feedback is a significant fraction of the total feedback and is strongly dependent on pressure in low pressure range and metal loading. These results suggest that radiative feedback should be considered in burn rate models of propellants which contain aluminum, magnesium, or boron as well as other metals.