COMBUSTION OF ALUMINUM PARTICLES IN A STREAM OF STEAM

Several models for aluminum combustion have been proposed, thus an overview of the combustion characteristics of aluminum powders is presented, taking into account both early and recent research activities and distinguishing between micron-sized and nano-sized aluminum. A collection of models for the two classes is discussed and compared, considering different environments in terms of oxidizers (H2O, O2, CO2), diluents (N2, Ar), temperature and pressure. In particular, the oxidation and the combustion of aluminum in steam are addressed, highlighting the oxidizing capabilities of various species. Different models are implemented for the complete description of aluminum combustion in the micron range, since smaller particles (1-10 μm) burn differently from bigger ones: both kinetics-based and diffusion-based processes are analyzed, stressing the role of reaction paths as well as diffusive phenomena. A single mechanism (kinetics-based) is identified and modeled for the combustion of nano-sized aluminum, outlining the limits and hypotheses for the application. For both sizes, only homogeneous reactions are considered and a model for the growth of an oxide cap on the surface of the particle is implemented. The results obtained are compared to the available numerical simulations and experimental evidence, aiming at the approximation of the burning time through the Dn law. Also, the profile over time of the temperature, the radius of the particle and the concentrations of the different chemical species involved in the reactions are analyzed.