Dissolution kinetics of carbon in aluminum droplet combustion: Implications for aluminized solid propellants

An analytical model describing the kinetics of carbon dissolution in burning aluminum droplets has been developed in order to simulate its effects under solid rocket motor conditions. A carbon dissolution rate (k) was introduced in different droplet regression laws and depending on the heterogeneous kinetics between the Al surface and the surrounding gases. The model was validated using previous experiments performed by the authors on millimeter-sized Al droplets burning in several CO₂-containing atmospheres at atmospheric pressure (P=1 atm). It has been shown that the carbon dissolution is affected by the presence of hydrogen due to competition between CO and H₂ chemisorption. The model was then applied to aluminized propellants (AP/HTPB) at high pressures (P=60 atm) and high temperatures (T=3000 and 3500 K), as well as at various burning rates and adsorption conditions. Though the accuracy of the extrapolation results needs further improvement, it has been shown that the carbon dissolution process should not be neglected in order to achieve global understanding of the combustion of Al particles, particularly agglomerates.