Ignition and combustion of Mg-Gd fuel in carbon dioxide

Magnesium combustion in carbon dioxide is considered an effective method for achieving in-situ resource utilization on Mars due to its high ignitability and the exothermic nature of the Mg-CO2 reaction. This study examined the ignition and combustion behavior of MgGd composite fuels with gadolinium content ranging from 10 % to 20 % in carbon dioxide. Using thermogravimetric analysis and time-resolved optical imaging techniques, we analyzed the thermal oxidation, ignition delay time, steady-state gas-phase combustion processes, and spectral characteristics of the composite fuels. Results indicated that magnesium particles doped with 15 % gadolinium exhibited a 1.7-fold increase in heat release rate compared to pure magnesium particles. Laser ignition experiments revealed that the combustion intensity of MgGd composite fuels significantly increased, accompanied by a high proportion of micro-explosions during combustion. Additionally, MgGd composite fuels exhibited a prolonged ignition delay time compared to pure magnesium particles in a 600 K carbon dioxide stream. The compositional analysis of combustion products indicated that gadolinium participates in reactions during combustion, forming gadolinium oxide with carbon dioxide. Based on these observations and measurements, a mechanism was proposed to explain how gadolinium doping enhances the heat release rate in magnesium particles. Overall, this study shows that doping gadolinium in lower total temperature carbon dioxide environments is beneficial for improving the heat release rate and combustion efficiency of magnesium particles through micro-explosive behavior. These findings could guide the development of magnesium-carbon dioxide reactions to improve the design of Mg-CO2 Mars powder propulsion systems.