Temperature measurements of aluminum particles burning in carbon dioxide

Aluminum particles are often added to solid propellants and explosives to enhance energy release, where the metal typically burns in mixtures of water vapor and carbon dioxide. In this study, information about the temperature field surrounding 5-10-μm aluminum particles burning at elevated pressure in CO₂/Ar and CO₂/N₂ is obtained via emission and absorption spectroscopy of AlO and three-color pyrometry. Spectra of AlO fit well to Boltzmann distributions and to similar temperatures of 3000 to 3200 K in both excited and ground states, suggesting that both states are in equilibrium. Pyrometry yields slightly lower temperatures, in the range of 3000 to 3100K. Both temperature ranges are well below the adiabatic flame temperature and the boiling point of alumina but are much closer to the predicted aluminum boiling temperature at elevated pressure. These results are consistent with a flame structure with combustion occurring at or very near the particle surface.