Reaction kinetics of an Mg/CO2 power system for Mars exploration

Abstract

This study investigates the heterogeneous and homogeneous reaction characteristics of the Mg/CO2 and coexisting Mg/CO systems using thermal analysis kinetics and quantum chemical calculation methods, respectively. The corresponding kinetic parameters are subsequently obtained using detailed theoretical calculations. The Mg/CO2 power system is a very promising propulsion mode for future Mars exploration due to the abundant carbon dioxide resources in the atmosphere of Mars. At present, much of the research on Mg combustion in CO2 has focused on the ignition and combustion characteristics at the macro level and few databases exist for microreaction characteristics. Three sets of thermal analysis experiments at different temperature rise rates are carried out in CO2 and CO atmospheres to extract the kinetic parameters. The results show that the heterogeneous reactions between Mg and CO2/CO are controlled by the first-order reaction model (F1), that is, by linear kinetics. There are two intermediate transition states in the homogeneous reaction between Mg and CO2. However, a suitable transition state structure is not observed in the homogeneous reaction between Mg and CO. The total energy barrier of this reaction is significantly higher than that of the Mg/CO2 reaction system. In addition, the rate constant of the Mg/CO2 homogeneous reaction is 10–17 orders of magnitude higher than that of the Mg/CO homogeneous reaction in the temperature range between the boiling point of Mg and 2000 K. The conclusions of this study are valuable for the combustion models of Mg/CO2 systems, which are expected to contribute to the structural design and optimisation of Mg/CO2 rocket engines or burners for Mars exploration.