A Comparison of Low-Pressure and Supercharged Operation of Polymer Electrolyte Membrane Fuel Cell Systems for Aircraft Applications

Multifunctional fuel cell systems are competitive solutions aboard future generations of civil aircraft concerning energy consumption, environmental issues, and safety reasons. The present study compares low-pressure and supercharged operation of polymer electrolyte membrane fuel cells with respect to performance and efficiency criteria. This is motivated by the challenge of pressure-dependent fuel cell operation aboard aircraft with cabin pressure varying with operating altitude. Experimental investigations of low-pressure fuel cell operation use model-based design of experiments and are complemented by numerical investigations concerning supercharged fuel cell operation. It is demonstrated that a low-pressure operation is feasible with the fuel cell device under test, but that its range of stable operation changes between both operating modes. Including an external compressor, it can be shown that the power demand for supercharging the fuel cell is about the same as the loss in power output of the fuel cell due to low-pressure operation. Furthermore, the supercharged fuel cell operation appears to be more sensitive with respect to variations in the considered independent operating parameters load requirement, cathode stoichiometric ratio, and cooling temperature. The results indicate that a pressure-dependent self-humidification control might be able to exploit the potential of low-pressure fuel cell operation for aircraft applications to the best advantage

Pressure-Dependent Operation of Polymer Electrolyte Membrane Fuel Cells; Exemplified by Aircraft Applications

The pressure-dependent operation of polymer electrolyte membrane fuel cell systems is considered, following a general research methodology. Based on previous research a model refinement from a phenomenological mathematical model towards a semi-empirical mathematical model is presented. It is shown that for the fuel cell device under test and the chosen compressor a low-pressure operation in suction mode is more efficient compared to the supercharged operation. This matter of fact permits optimized operating and control strategies for (multifunctional) fuel cell systems for aircraft applications

Multifunctional System Integration of Fuel Cells aboard Civil Aircraft – Status Quo

The Advisory Council for Aviation Research and Innovation in Europe (ACARE) has imposed itself ambitious objectives concerning industrial leadership, safety and security as well as emissions reduction within civil aviation toward the years 2020 and 2050, respectively. Integration of electrochemical energy conversion technologies in form of secondary batteries, fuel cells or supercapacitors shows significant potential to reduce emissions of both contaminants and noise aboard future generations of aircraft. With its group Energy System Integration (ESI) the Institute of Engineering Thermodynamics (TT) at the German Aerospace Center (DLR) performs applied research and development with respect to innovative electrochemical energy conversion and storage technologies; thereby, research focusses on emergency and auxiliary power for more-electric civil aircraft as well as propulsion power for small all-electric aircraft. A promising approach is the multifunctional system integration of lowtemperature polymer electrolyte membrane fuel cells (LT-PEMFC) exploiting not only their electric output power but also their waste heat, process water and oxygen-depleted air (ODA) for an effective and efficient integration into aircraft system architectures. The present talk summarizes the most recent research and development results concerning multifunctional fuel cell systems (MFFCS) for emergency and/or auxiliary power generation aboard future generations of civil aircraft, with special emphasis on conceptual designs and operation strategies. Based on measurement data and theoretical studies revealing the multipurpose power demand of existing civil short- & mid-range aircraft, general requirements are derived to dimension MFFCS. It is shown that with existing fuel cell technology it is feasible to fulfill these requirements; however, novel conceptual designs for both electric and process engineering interconnection of MFFCS demonstrate the potential to optimize the dynamical behavior and/or the degradation process of the fuel cell stacks. This potential is utilized to develop optimum power point tracking method for arrays possessing several fuel cell stacks in multifunctional system integration and deduce operation strategies for MFFCS. Finally, an outlook is provided specifying and discussing the next steps for further research and development toward a practical multifunctional system integration of fuel cells in future generations of civil aircraft

Hybrid fuel cell power modules in more- and all-electric aircraft

Aviation industry has put much effort into reducing noise, exhaust and other factors affecting the environmental footprint of aircraft. Future goals are set high and require much research in the fields of alternative fuels as well as alternative power sources and propulsion technologies. A very promising candidate is the combination of hydrogen fuel cells, batteries and electric propulsion. Together these technologies provide a solid basis for quiet, non-polluting commuter or regional passenger aircraft within a 2050 timeframe. To achieve this vision the technology must be further matured in a multi-iteration development process. To date hydrogen aircraft have mostly been proof of concept prototypes, lacking range, durability, reliability and payload requirements of the targeted aircraft. In an ongoing joint effort the all-electric HY4 will allow achieving the next steps of this process, pushing boundaries of passenger count, altitude, range and reliability. In a parallel development applying this technology to an APU replacement for commercial more electric aircraft enables aviation to profit sooner. Due to the reduced requirements in terms of power and energy a replacement unit for an A320 type aircraft could be ready for use in the 2025 timeframe. This would enable green taxiing and emission free ground operation of these aircraft. The presentation will discuss the current status of the HY4 project and the feasibility of a redundant fuel cell based high dynamic multifunctional APU replacement with improved controls for simultaneous electrical power and optimized ODA production for tank intertization