Simulation of aluminumflame structure relating to the importance of heterogeneous surface reactions

摘要

Surface reactions occur during the combustion of aluminum particles in various environments. In solid-propellant/rocket-motor conditions (at agglomerated particle sizes greater than 100 μm and pressure greater than 6.0 MPa), the gas-phase flame dominates the heat feedback to the molten aluminum particle and consumption of the aluminum particle. Combustion regimes where the gas-phase flame dominates have been the focus of much experimental and computational research. Recent experimental and computational work has shown that at low pressures and small particle sizes the kinetic rate of reaction is slower compared to the diffusion rate of the species moving the gaseous flame closer to the surface. This paper reports the results of aluminum particle combustion simulations over a wide range of oxidizer concentrations, pressures, and particle diameters depicting the transition regime from diffusion reactions to kinetic reactions. Calculated burn times are compared with experimental data. Computed flame structures under the various experimental test conditions are compared. Calculated species profiles are used to determine which species are present at the particle surface in the different combustion regimes. Calculations were performed to compare when the simulations transition to kinetic-controlled combustion in oxidizing environments made up of CO_2, H_2O, and O_2. The calculations focus on the transition regime and do not consider the actual surface reactions of the aluminum particle.