Optimized hydrogen fuel cell systems for MOA and all electric propulsion drivetrains

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Optimized hydrogen fuel cell systems for MOA and all electric propulsion drivetrains


application/pdf Optimized hydrogen fuel cell systems for MOA and all electric propulsion drivetrains Josef Kallo, Johannes Schirmer, Claudia Wernera, Lucas Busemeyera, Gunnar Preissa, Florian Goresa, Oliver Thalau, Torben Bu


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            <title>Optimized hydrogen fuel cell systems for MOA and all electric propulsion drivetrains</title></titles>
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	    <date dateType="Created">Mon 20 Mar 2017</date>
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            <date dateType="Submitted">Thu 15 Mar 2018</date>
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Optimized hydrogen fuel cell systems for MOA and all electric propulsion drivetrains Josef Kallo* b , Johannes Schirmer*, Claudia Werner a , Lucas Busemeyer a , Gunnar Preiss a , Florian Gores a , Oliver Thalau*, Torben Burberg* * German Aerospace Center, Institute of Engineering Thermodynamics, Pfaffenwaldring 38, 70569 Stuttgart, Germany a German Aerospace Center, Institute of Engineering Thermodynamics, Hein-Saß-Weg 38, 21129 Hamburg, Germany b corresponding author, josef.kallo@dlr.de, Tel: +49 711 6862672 Abstract: The increasing electrification of aircraft systems from simple actuators to “green taxi” and main electric propulsion typifies a wide field for interdisciplinary research. The German Aerospace Center in Stuttgart, mainly represented by the “electrochemical systems” group at the Institute of Engineering Thermodynamics intensified its activities since 2007 in this interesting research field. Main topics of the research are the development and optimization of high efficient power generators and complete electrical power trains based on hydrogen fuel cells, batteries, efficient voltage converters and high torque electrical motors for General Aviation and commercial aviation. Introduction A possible path to improve the efficiency of electric power supply system on board of an aircraft is the usage of hydrogen fuel cells and battery hybrids. The focus for the commercial aviation lies on APU replacement and multifunctional upgrade. Addressed functions include the efficient general electrical power production on board, production of oxygen depleted air (ODA) as fire suppressor medium and the onboard production of water. The same system can be used as a power generator for an electrical driven propulsion system to move the aircraft on ground or an emergency power system. Mainly for the General Aviation, an adapted fuel cell system can be used as a power generator unit for the main aircraft propulsion during flight. Therefore the lightweight and the maximized efficiency coupled with an high redundancy and reliability play a major role. Started in 2009 with a “one seater” all electric fuel cell driven aircraft, todays development shows the near term feasibility of a “four seater” and the perspective beyond. Main Content This oral presentation will give as an introduction a short overview of the hydrogen fuel cell system and the “green taxi” nose wheel propulsion system implemented and tested together with Airbus in the German Aerospace Center’s A320 research aircraft D-ATRA. Picture 1 shows such a device. A low temperature PEM (Polymer Electrolyte Membrane) fuel cell was used for the tests conducted in Hamburg. Hydrogen storage systems with 350 bar and a custom made design fuel cell were implemented in the back cargo room of the plane. The motor inverter and control unit was implemented in the forward part of the cabin, DC power lines (300V) were used to transport the electrical energy from the fuel cell to the motor inverter. Picture 1: electric nose wheel drive A320 (courtesy Airbus) Based on a further developed architecture, one of the main messages of the presentation will include the feasibility of a redundant four fuel cell system cluster with improved controls for simultaneous electrical power and optimized ODA production. Picture 2 shows a process technology draft of such a cluster of two parallel 10kW and two parallel 30 kW systems. Power charts will be shown to explain the dynamic behavior of such a configuration. Picture 2: System draft of a four fuel cell system cluster for simultaneous optimized electrical power and ODA generation Using this configuration, the cathode stoichiometry of a fuel cell system can be minimized to achieve an improved constant oxygen depleted air flow, whereupon a second system uses a higher cathode stoichiometry for improved efficiency and high power capability. During the descent phase, when a high ODA flow is required, the second system can also use an optimized cathode stoichiometry, fully aware that system number three and four can pitch in from standby. Picture 3 shows the possible cathode stoichiometry for such a flight. Picture 3: Different cathode stoichiometry combination for different flight phases As an outlook the fuel cell system controls can be further adjusted to work properly at air pressures lower than 0,3 bar absolute. This ensures an efficient and safe operation of a fuel cell system without sophisticated compressor units, only by using a low overpressure blower (max. 100mbar overpressure) for the cathode air supply from the outside environment. The fuel cell system model developed at the German Aerospace Center in Stuttgart show an expected efficient utilization of such a system by adjusting the temperature controls. Picture 4 shows the calculated working boundaries of the temperature and the cathode stoichiometry at lower cathode air pressure. A detailed explanation of the controls background will be presented based on the stack temperature variation. Picture 4: Calculated operating window for a low temperature PEM fuel cell at low cathode pressure Finally, the feasibility of a hydrogen fuel cell and battery hybrid system as power source for aircraft propulsion (Antares DLR H2) was shown in the past years. Picture 5 show the Antares DLR H2 during a cross country flight from Berlin to Stuttgart. Picture 5: Antares DLR H2 during a cross country flight in 5000ft MSL As an integrated result, the further development of this “main propulsion path” includes the system architecture and it’s optimization regarding reliability and redundancy. Therefore an improved fuel cell system consisting of four independent in series coupled subsystems was developed. Experiments showed the capability of extracting one of the subsystems during maximum electrical load, simulating the complete malfunction of such a subsystem without a negative effect on the remaining three subsystems. Propelling a 850kg electrical driven aircraft at a peak overall system efficiency of >40% and a speed of 125km/h, the hydrogen consumption lies at around 1kg/100km.