Application of Solid Oxide Fuel Cells to Aircraft

Abstract

Fuels Cells are being considered for various applications on airplanes and space vehicles. It is critical that fuel cells meet the performance and airplane system-level environmental requirements. Fuels cells are being considered for replacing batteries as a non-time limited emergency power source; as a replacement for the Auxiliary Power Units (APUs); and as the primary power source for propulsion on high altitude long endurance aircraft and high altitude airships. For high altitude long endurance airplane or airship applications, fuels cells are being considered as regenerative closed loop power sources. Two major types of fuel cells, Proton Exchange Membrane Fuel Cell (PEMFC) and Solid Oxide Fuel Cell (SOFC), are the most probable choices due to their relatively high level of development and potential for commercialization. For transportation applications, the PEMFC is in the forefront because of its compact size, quick startup time and low operating temperatures (∼80°C). In the future, for aerospace applications, the SOFC should become more common because of its ability to use converted hydrocarbon fuels along with some of the impurities such as CO, its high operating temperatures (∼1,000°C) and its potential to combine with a gas turbine to gain even higher efficiency (1). For use on present day airplanes, since the operators of commercial airplanes have no desire to maintain the logistics and carry another type of fuel (e.g. Hydrogen), fuel processing is required to convert current fuels, such as Jet A, JP-5 or JP-8 to hydrogen in order to drive the fuel cells. The complexity of the fuel processing is dependent on the purity required. Here, the SOFC seems to have a definite advantage over the PEMFC.