Fuel Cell Hybrid Propulsion Challenges and Opportunities for Commercial Aviation

Abstract

This paper highlights challenges and opportunities associated with possible future fuel cell hybrid propulsion systems for commercial aviation applications. Key performance characteristics of fuel cells are highlighted v is a v is gas turbines. Several gas turbine-fuel cell hybrid concepts are described and one of these is considered in detail for a narrowbody commercial airliner application. Various observations and conclusions are presented with regards to fuel cell, electric power, and gas turbine subsystems and the potential viability of fuel cell hybrids for future commercial aviation application. I. Introduction MPROVEMENTS in electric power generation and storage technology, driven largely by demand in the automotive and portable computing (laptop) industries, are leading to growing interest in electric and hybridelectric aircraft propulsion. These improvements are enabling incremental advances in electric aircraft propulsion, from experimental demonstrations in niche applications towards practical use in mainstream applications. This is evidenced by the fact that there are now production electric-powered manned aircraft available (e.g. Antares 20E Sailplane, Lange Aviation), with still more planned for production. The practical applications for electric and hybrid aircraft are presently restricted to remote control hobby aircraft, small unmanned aerial vehicles (UAVs), sailplanes, motorgliders, and light experimental airplanes. These applications have modest energy and power requirements (in the Watt to Kilowatt range) and are comparatively insensitive to propulsion system weight and volume. These characteristics make the above applications conducive to using today’s battery, electric motor, and fuel cell technology as a means of propulsion. In contrast, typical commercial aviation applications require much more energy and higher power output levels (in the Megawatt range) and are more sensitive to weight. Gas turbines powered by Jet-A fuel far outstrip the energy/weight and power/weight capabilities of electric storage and power in this arena. However, the pace of advancement in electric power and storage technology appears to be outpacing advances in gas turbine technology. If this trend continues over a span of decades, it is reasonable to expect that electric motor, battery, and fuel cell technology will at length become practical for commercial aviation. It is therefore worthwhile to examine electric and fuel cell propulsion concepts in the context of commercial propulsion applications in order to ascertain what might be possible in the future as well as to identify what barriers must be overcome. The focus of this paper is on commercial transport aircraft targeted for a 2035 entry into service (EIS). There are many possible configurations one might consider for a hybrid electric propulsion system. This paper focuses only on gas turbine-fuel cell hybrid propulsion systems, to the exclusion of other possible arrangements. This was done to limit the scope of this paper and with full recognition that there may be other hybrid concepts worth studying.