Reactive Molecular Dynamics Simulation on the Carbon Deposition of the Combustion of Al Particles in CO2

Combustion of Al particles in CO2 is a widely encountered scenario in solid propellants, where the formation of C deposition can lead to insufficient combustion and severely hamper energy release. This study investigates the combustion of Al/CO2 and elucidates the C deposition mechanism therein through reactive molecular dynamics simulations. The C deposition is initiated with the chemisorption of CO2, followed by reactive diffusion to form C chains (C2). These C chains then gradually agglomerate into larger clusters and amorphous aluminum oxycarbide with a chemical composition of AlO0.03-0.35C0.69-1.54. Therein, Al atoms serve as connectors of C chains and a few O atoms on the surface. As the concentration of CO2 increases, longer C chains form, and the final C content reaches 12.3%, close to the saturation limit proposed by experiments. Moreover, the CO2 concentration corresponding to a C/Al molar ratio of 0.37 is conducive to efficient and sufficient energy release. These results are expected to deepen our understanding of C deposition and provide theoretical guidance for improving the combustion efficiency of Al particles in CO2.