Experimental characterization of lithium-carbon dioxide combustion in batch reactors for powering Venus landers

Abstract

The extreme environment and low solar availability on the surface of Venus translate to significant power and thermal management challenges for landed missions. The longest mission to the surface of Venus was Venera 13, which operated for ~2 h. To increase duration and scientific scope, future missions will require power systems with greater specific energy to support active cooling. In-situ resource utilization (ISRU) combustion power systems have been proposed with lithium fuel and the ambient atmosphere (96.5% CO2, 3.5% N2) as the oxidizer. Conceptual designs have assumed batch reactors, which may vary in behavior as fuel is consumed and product concentration increases. As such, practically achievable reaction yield and system-specific energy are unknown. In this study, Li-CO2 batch combustion tests were performed to determine such reaction parameters. Five tests were performed with different operating temperatures, heat delivery mechanisms, and approaches for contacting fuel and oxidizer. Fuel utilization was found to generally increase with bulk reactor temperature. At 500–750 °C, fuel utilization was only 40–60%. This increased to ~98% at 900 °C, corresponding to an effective specific energy of 25.6 ± 0.7 MJkgLi−1 based on reactant and product enthalpies. However, endothermic decomposition of produced Li2CO3 occurs at higher temperatures, limiting specific energy. Based on fuel utilization, the lower temperature cases achieved 32–41 MJkgLi,reacted−1. Attempts to increase lower temperature reaction yield were unsuccessful in this investigation. Further development of approaches to improve yield could enhance the technical potential of lithium combustion power systems.