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.