Revealing Al–O/Al–F reaction dynamic effects on the combustion of aluminum nanoparticles in oxygen/fluorine containing environments: A reactive molecular dynamics study meshing together experimental validation

Abstract

Improving the energy conversion efficiency in metallic fuel (e.g., Al) combustion is always desirable but challenging, which often involves redox reactions of aluminum (Al) with various mixed oxidizing environments. For instance, Al–O reaction is the most common pathway to release limited energy while Al–F reaction has received much attentions to enhance Al combustion efficiency. However, microscopic understanding of the Al–O/Al–F reaction dynamics remains unsolved, which is fundamentally necessary to further improve Al combustion efficiency. In this work, for the first time, Al–O/Al–F reaction dynamic effects on the combustion of aluminum nanoparticles (n-Al) in oxygen/fluorine containing environments have been revealed via reactive molecular dynamics (RMD) simulations meshing together combustion experiments. Three RMD simulation systems of Al core/O2/HF, n-Al/O2/HF, and n-Al/O2/CF4 with oxygen percentage ranging from 0% to 100% have been performed. The n-Al combustion in mixed O2/CF4 environments have been conducted by constant volume combustion experiments. RMD results show that Al–O reaction exhibits kinetic benefits while Al–F reaction owns thermodynamic benefits for n-Al combustion. In n-Al/O2/HF, Al–O reaction gives faster energy release rate than Al–F reaction (1.1 times). The optimal energy release efficiency can be achieved with suitable oxygen percentage of 10% and 50% for n-Al/O2/HF and n-Al/O2/CF4, respectively. In combustion experiments, 90% of oxygen percentage can optimally enhance the peak pressure, pressurization rate and combustion heat. Importantly, Al–O reaction prefers to occur on the surface regions while Al–F reaction prefers to proceed in the interior regions of n-Al, confirming the kinetic/thermodynamic benefits of Al–O/Al–F reactions. The synergistic effect of Al–O/Al–F reaction for greatly enhancing n-Al combustion efficiency is demonstrated at atomic-scale, which is beneficial for optimizing the combustion performance of metallic fuel.