Combustion wave propagation in magnesium/water mixtures: Experiments and model

Metal (Al, Mg)/water mixtures are of interest for hydrogen generation and propulsion. Due to the highly exothermic metal water reaction, such mixtures, upon ignition, exhibit self-sustained propagation of combustion wave with simultaneous release of hydrogen from water. In this work, experiments with stoichiometric Mg/H2O mixtures were conducted. Uniform propagation of the combustion wave was observed, and the effect of metal particle size, in the range 75-1501 mu m, on the combustion front velocity was determined. Based on the obtained results, a mathematical model for combustion wave propagation in Mg/H2O mixtures was developed. In this model, the combustion wave structure includes a thin water-boiling front, a preheat zone with water vapor flowing through the porous medium and a wide zone of reaction between the formed water vapor and the metal. This diffusion-limited model, solved analytically, predicts the front velocity and thermal profile of the combustion wave for different metal particle sizes. A satisfactory agreement between the experimental and modeling results is demonstrated, and features to improve the model are identified. With some modifications, the model can also be applied to combustion wave propagation in nanoaluminum/water mixtures. (C) 2009 Elsevier Ltd. All rights reserved.