Revealing Pressure Effects in the Anisotropic Combustion of Aluminum Nanoparticles

The anisotropic combustion of aluminum nanoparticles (ANPs) under
the flow impact is examined in a wide pressure range from 5 to 100
atm using reactive molecular dynamics simulations. A model of energy
transfer in flow–particle interactions is constructed to describe
the correlation between the energy transfer rate and flow properties.
We find that the intensity of flow–particle interactions is
proportional to the product of flow pressure and the cubic of the
flow velocity in the anisotropic combustion of ANPs. Three combustion
modes are identified from numerical simulations as diffusion oxidation,
anisotropic oxidation, and microexplosion. Two critical thresholds
of the energy transfer rate between the flow and the particle are
further derived to distinguish the combustion modes. An energy transfer
rate of 10 K/ps is the first critical threshold separating diffusion
oxidation and anisotropic oxidation, as a temperature gradient exists
in ANPs. Further increasing the energy transfer rate to a critical
value of 86 K/ps, the rapid energy transfer is sufficient to induce
massive surface evaporation leading to microexplosion. These two criteria
are generalized to separate the combustion behaviors of ANPs. The
proposed anisotropic energy transfer model is competent in predicting
the combustion modes of ANPs and describing the energy transfer on
the particle surface.