On the Role of Carbon Dioxide in the Combustion of Aluminum Droplets

Aluminum combustion in wet and dry CO2: Consequences for surface reactions

“…It was also observed that the presence of nitrogen promotes the oxide cap formation, while the addition of inert gases (Ar, He) seems to inhibit it [3,17,18]. In [2,19], it was shown that the oxide cap size decreases during Al burning in watercontaining atmospheres; an oxide cap regression rate was estimated in analogy to the burning rate, and was correlated with the droplet temperature, suggesting a chemical decomposition process of alumina by liquid aluminum into gaseous species.…”

“…It was also found that the excess of dissolved carbon resulting from the permanent consumption of the Al particle is finally ejected at the surface. This carbon coating prevents Al vaporization and stops the gas-phase burning [19]. However, under solid propellant conditions, as aluminum burns in hot gases (T > 2500 K), surface reactions may still occur even if there is no more gas-phase combustion.…”

“…The dissolution process of oxygen and carbon inside the particle is also significant. The quantities dissolved in the unburnt residue can reach about 8-10 mol% O, and 18-23 mol% C [18][19][20]. In fact, the carbon concentration corresponds to the carbon saturation limit in liquid aluminum.…”

“…Furthermore, the existence of the second combustion regime suggested by [19] is examined. Accordingly, an experimental setup which has been developed to observe millimeter-sized aluminum droplets burning in cold gases is used to simulate the hot atmospheres under solid propellant conditions by a permanent laser heating.…”

“…In [19], we have especially studied the combustion of Al droplets in CO 2 /H 2 O mixtures because both gases correspond to the main oxidizers produced during the solid propellant decomposition (x H 2 O ≈ 0.4-0.5, x CO 2 ≈ 0.1). Although high CO 2 concentrations were examined (up to 97% CO 2 = wet CO 2 ), Al burning in pure CO 2 (dry CO 2 ) was not studied.…”