Effects of particle size and pressure on combustion of nano-aluminum particles and liquid water

The combustion wave propagation of nanoaluminum-water mixtures is studied theoretically and experimentally for particles in the size range of 38-130 nm and over a pressure range of 1-10 MPa. A multi-zone framework is established to predict the burning properties and flame structure by solving the conservation equations in each zone and enforcing the mass and energy continuities at the interfacial boundaries. The flame properties are measured by burning nanoaluminum-water strands in a constant-volume vessel. The present study deals with the downward propagating flame. Emphasis is placed on the effects of particle size and pressure. An analytical expression for the burning rate is derived, and physicochemical parameters that dictate the flame behavior are identified. For conditions present in the study, the burning rate shows pressure and particle size dependencies of the form rb[cm/s]=98.8×(p[MPa])0.32(dp[nm])-1.0. The flame thickness increases with increasing particle size and decreasing pressure. Results support the hypothesis that the combustion of aluminum-water mixtures is controlled by mass diffusion across the oxide layers of the particles.