Humidifier-Less Fuel Cell Systems for Improved Gravimetric Power Densities in Aircraft Applications

Abstract

Proton exchange membrane fuel cells (PEMFC) are regarded as a promising technology for low-emission aircraft. However, for fuel cell-powered aircraft to become viable, the gravimetric power density must increase significantly, from currently 0.5 kW/kg to 2.0 kW/kg at system level. While state-of-the-art fuel cell systems use an air humidifier to improve the fuel cell water management, this study investigates how removing the humidifier could improve the gravimetric power density while maintaining a high system efficiency. A one-dimensional, PEMFC stack model that incorporates water management effects is combined with auxiliary component models to relate cell-level phenomena to system-level complications. Through numerical optimization of operating conditions, the interdependencies between efficiency, system mass, and internal drag of the fuel cell cooler are explored, and the adaptation of operating strategies for dry conditions is examined. The results indicate that eliminating the humidifier improves the gravimetric performance of the fuel cell system by 6 %, without significantly affecting hydrogen consumption. Additionally, it was observed that the cooling demand of the fuel cell stack decreased by 4%. Based on these findings, specific requirements for an aviation fuel cell stack are proposed that could further enhance the benefits of removing the humidifier.