Fuel cell APU for commercial aircraft

Commercial aircraft are increasingly faced with the requirement of simultaneously reducing fuel use and emissions. Thus, new technologies are required to be developed and implemented to solve this dilemma. One such technology is the fuel cell. Utilizing a similar operation principle to that of a battery, fuel cells harness an electrochemical process to very efficiently produce Direct Current (DC) electricity from fuel. If a fuel cell were to replace a current turbine powered Auxiliary Power Unit (APU), the benefits would most likely include; cutting fuel used by the APU more than half, reduced noise, reduced emissions, fewer moving parts, improved reliability, reduced capital costs, and would also enable the production of water. These benefits may outweigh the anticipated weight and volume penalties associated with fuel cells. Given the rate of progress in reducing the fuel cell's weight and volume, as well as the projected capability to use common fuels, it is projected that fuel cells will reach a high enough maturity level within the next 10-15 years to be considered for use in commercial aircraft. A More Electric Airplane (MEA) is the next step in aircraft design philosophy that has been proposed by some(1). Such an aircraft will use electricity instead of pneumatic and hydraulic energy to power the aircraft's various systems, such as environmental control. With the pneumatic requirements removed from the APU, a MEA architecture would ideally be suited for a fuel cell APU application. Together, the Boeing company, industry organizations, fuel cell manufacturers, and academia are currently conducting research to evaluate the system level benefits of a future fuel cell APU. This paper describes the MEA study airplane platform, the chosen fuel cell type, fuel cell APU installation, operational requirements, and also provides an initial systems-level performance assessment (as compared to a turbine powered APU). © 2003 by The Boeing Company. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.