Uwe Wollrab

Performance Assessment of Turbocharged Pem Fuel Cell Systems for Civil Aircraft Onboard Power Production

Stefano Campanari Associate Professor e-mail: stefano.campanari@polimi.it Giampaolo Manzolini Research Engineer e-mail: giampaolo.manzolini@polimi.it Andrea Beretti Research Engineer Dipartimento di Energetica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy Uwe Wollrab Systems Engineering, Fuel Cell Systems Development, AIRBUS Deutschland Gmbh, 21129Hamburg, Germany e-mail: uwe.wollrab@airbus.com Performance Assessment of Turbocharged Pem Fuel Cell Systems for Civil Aircraft Onboard Power Production In recent years, civil aircraft projects are showing a continuous increase in the demand of onboard electrical power, both for the partial substitution of hydraulic or pneumatic controls and drives with electrical ones, and for the consumption of new auxiliary sys- tems developed in response to flight safety and environmental control issues. Aiming to generate onboard power with low emissions and better efficiency, several manufacturers and research groups are considering the possibility to produce a relevant fraction of the electrical power required by the aircraft by a fuel cell system. The first step would be to replace the conventional auxiliary power unit (based on a small gas turbine) with a polymer electrolyte membrane (PEM) fuel cell type, which today is favored with respect to other fuel cell types; thanks to its higher power density and faster startup. The PEM fuel cell can be fed with a hydrogen rich gas coming from a fuel reformer, operating with the same jet fuel used by the aircraft, or relying on a dedicated hydrogen storage on- board. The cell requires also an air compression unit, where the temperature, pressure, and humidity of the air stream feeding the PEM unit during land and in-flight operation strongly influence the performance and the physical integrity of the fuel cell. In this work we consider different system architectures, where the air compression system may exploit an electrically driven compressor or a turbocharger unit. The compressor type and the system pressure level are optimized according to a fuel cell simulation model, which calculates the cell voltage and efficiency as a function of temperature and pressure, calibrated over the performances of real PEM cell components. The system performances are discussed under different operating conditions, covering ground operation, and in- termediate and high altitude cruise conditions. The optimized configuration is selected, presenting energy balances and a complete thermodynamic analysis. 关DOI: 10.1115/1.2772636兴 Introduction New projects of civil aircrafts are in these years frequently influenced by a development strategy focusing on more electric aircraft 共MEA兲 or even all electric aircraft 共AEA兲 concepts. The partial substitution of conventional hydraulic or pneumatic con- trols and drives with electrical ones 共see Table 1兲, and the intro- duction of new auxiliary systems bring about an increase in on- board electric power consumption, reaching values around 560 kW for airplanes such as the B777 or A330/A340, and going toward 1.3– 1.5 MW for next generation aircrafts 关1–5兴. Furthermore, the possible elimination of power offtakes from the main engines would increase the nominal power output re- quired by a separated onboard electricity generator. It is well known that a fraction of electric power is generated on-board civil aircrafts by small turbine units, acting as auxiliary power units 共APUs兲. Such machines operate with simple cycle, uncooled operation, low turbine inlet temperature 共TIT兲, and pres- sure ratio, generally with single stage radial compressor and a power output in the range of several tenth kilowatts and up to the hundred kilowatt scale. Their advantages include low weight, rapid startup, and robustness; disadvantages are primarily the low efficiency 共15–18%兲 and significant NO x and CO emissions. The Contributed by the International Gas Turbine Institute of ASME for publication in the J OURNAL OF E NGINEERING FOR G AS T URBINES AND P OWER . Manuscript received April 28, 2007; final manuscript received May 9, 2007; published online February 29, 2008. Review conducted by Dilip R. Ballal. Paper presented at the ASME Turbo Expo 2007: Land, Sea and Air 共GT2007兲, Montreal, Quebec, Canada, May 14–17, 2007, Paper No. GT2007-27658. possible removal of power offtakes from the main engines would increase the nominal power of the APU system, making more important to look for higher efficiency and lower pollution de- vices. Polymer electrolyte membrane fuel cells 共PEM FCs兲 on their own are widely experimented in prototypes and generally recog- nized very attractive for future application in the automotive field; thanks to their ability to generate electricity with high efficiency 共e.g., 50–55%兲 in tenth-kilowatt scale systems fed with hydrogen and operating at low temperatures 共60– 70° C兲. They also show a rather high power density 共in terms of kW/kg and kW/ dm 3 兲, fast startup, and negligible emissions. The quick development of this technology has suggested to consider their application also in the aeronautic field, within the perspective of a step by step develop- ment, which could also represent a new possible market for the beginning of their commercialization. The technology roadmap for this development includes several steps, where the first should be introducing a pure hydrogen PEM system with minor aircraft changes, aiming to provide a fraction of electric power 共well below the potential power requirements shown in Table 1兲 for auxiliary loads and emergency systems actually sustained by APUs and other generators 共for instance, the air turbine that is used to drive the pumps of the emergency hy- draulic circuit兲. Subsequent steps could involve the use of onboard reformers 关3兴 as well as different FC types with increasing power output. The concept of integrating a PEM unit onboard civil aircrafts has been already introduced in several works 关2,6,7兴, where the fuel cell has been generally considered as a device with assigned Journal of Engineering for Gas Turbines and Power Copyright

Performance assessment of turbocharged PEM fuel cell systems for civil aircraft onboard power production

In recent years, civil aircraft projects are showing a continuous increase in the demand of onboard electrical power, both for the partial substitution of hydraulic or pneumatic controls and drives with electrical ones, and for the consumption of new auxiliary systems developed in response to flight safety and environmental control issues. Aiming to generate on-board power with low emissions and better efficiency, several manufacturers and research groups are considering the possibility to produce a relevant fraction of the electrical power required by the aircraft by a fuel cell system. The first step would be to replace the conventional auxiliary power unit (APU, based on a small gas turbine) with a Polymer Membrane fuel cell type (PEM), which today is favored with respect to other fuel cell types thanks to its higher power density and faster start-up. The PEM fuel cell can be fed with an hydrogen rich gas coming from a fuel reformer, operating with the same jet fuel used by the aircraft, or relying on a dedicated hydrogen storage onboard. The cell requires also an air compression unit, where the temperature, pressure and humidity of the air stream feeding the PEM unit during land and in-flight operation strongly influence the performance and the physical integrity of the fuel cell. In this work we consider different system architectures, where the air compression system may exploit an electrically driven compressor or a turbocharger unit. The compressor type and the system pressure level are optimized according to a fuel cell simulation model which calculates the cell voltage and efficiency as a function of temperature and pressure, calibrated over the performances of real PEM cell components. The system performances are discussed under different operating conditions, covering ground operation, intermediate and high altitude cruise conditions. The optimized configuration is selected, presenting energy balances and a complete thermodynamic analysis.Copyright