Skip to main content

Microtubular Solid Oxide Fuel Cell Power System developement and integration into a Mini-UAV

Final Report Summary - SUAV (Microtubular Solid Oxide Fuel Cell Power System developement and integration into a Mini-UAV)

Executive Summary:
The SUAV-project developed SOFC-technology and a system, which is hybridized with a battery to power an Unmanned Aerial Vehicle (UAV). It comprises a mSOFC stack, CPOx reformer to generate reformate gas from propane, a propane tank, a battery, and additional BoP components. Sizing of power and the dimensions were done by analyzing flight data of an existing battery-powered UAV and selecting a typical UAV.
The project ran from November 2011 until November 2015. Half way the project it was decided to have two parallel development routes to mitigate technical risks; a SUAV-classic route as originally planned, and the SUAV-Alternative core route
For the SUAV-classic system the activities were focused on optimization of the cells, manufacturing and integrating technologies as well as stack and system design. As the pod of the UAV is cylindrical a system and stack design of a similar shape was pursued.
The performance of the cells was increased from initially 5 W to an excess of 8 W/cell, as a result of changes in cell design and manufacturing. A stack concept incorporating 48 tubes has been designed. CFD analysis aided in the design. After several iterations in conjunction with the system design a final stack design was made, and two stacks were build. Stack 1 failed unexpectedly due to the use of unsuited equipment for testing. Based on the post-test analysis of stack 1 small modifications were made to the stack design before stack 2 was built. Stack 2 showed that 335W could be achieved at 0.7 V, exceeding the target value of 310 W. This shows that the stack has a sufficiently high power density to be used in an UAV. Unfortunately this stack also suffered failure a short way in to the test. As a result no stack was available for use in the prototype.
A number of system concepts were developed for the entire power generator, differing in the way the air flows are guided through the system. Based on weight and volume considerations a final concept was selected. Extensive CFD studies were performed to support the design and determine the main dimensions. The system comprises the following sections: reformer, burner, recuperator, and insulation. An important factor for dimensioning the system were the limits of the allowed pressure losses.
The system weight was minimized by limiting the number of annular spaces, keeping the length of each section to the minimum, and by using thin metal walls (in combination with the removal of metal in places where a high strength is not required). This resulted in power density of the system better than commercially available systems.
Due to damage of the two built fuel cell stacks no stack was available for testing within the system. In order to allow functional testing of the system and its components a dummy stack was designed and made, consisting of 10 steel tubes with a pressure drop resembling the pressure drop of an actual stack. After integration of BoP components with the “dummy” system container, phases of a flight were tested, a start-up, partial load and full load simulation and a controlled shut-down and cool-down and a quick restart.
The tests have shown that the system meets its design objectives: it is capable to provide the right environment for a solid oxide fuel cell, it can be started up quickly, and a safe shut-down can be warranted keeping the fuel cell reducing according to the requirements. The system temperatures are well-controllable by variation on the blower and valve settings (as devised).
With the developed technology it is possible to build a small scale power-unit, powered by propane, if a suitable fuel cell is integrated. At this scale, it is possible to use the system as range extender for UAV’s.
Within the SUAV-Alternative route the commercial SOFC system was integrated with battery pack for laboratory testing. Different mission profiles were simulated with the complete system in the lab. It was concluded that the integrated system is suitable for a UAV mission.
Using the experimental results a CFD model was set-up and validated to determine the temperature profile. Using the CFD model a design for a pod has been made.
Due to time limitations it was not possible to manufacture a new pod for an actual air mission.

Project Context and Objectives:
SUAV aims to design, optimise and build a 310W mSOFC stack, and to integrate it into a hybrid power system comprising the mSOFC stack and a battery. Additional components of the system are a CPOx processor to generate reformate gas from propane and other equipment for the electrical, mechanical and control balance of plant (BoP).
All these components will be constituents of an entire fuel cell power generator which will first be tested in the lab and, after further optimisation and miniaturisation, in a mini UAV (Unmanned Aerial Vehicle) platform. SUAV is primarily aiming at the DVF2000 UAV platform from SurveyCopter (France) but will consider other options too.
Propane was chosen as the fuel due to its superior energy density compared to hydrogen. Solid Oxide Fuel Cell (SOFC) technology was chosen since it can convert reformate (CO/H2-mixtures) to electricity, as compared to other types of fuel cell that require pure hydrogen, which significantly reduces complexity and thus size and weight of fuel processing.

Project Results:
see attachment

Potential Impact:
0 Impact
The impact from the R&D done within the SUAV project can be divided in various categories:
- Technical impact
- Commercial
- International
- Educational
- Integration in Europe
- Environmental

0.1 Technical impacts
Within the project SOFC technology and an hybrid system has been developed capable of providing power to an UAV. In more detail the following technical improvements were reached.

• A tubular mSOFC stack has been developed having a high power density better than 280 W/l.
o mSOFC tube manufacturing methods have been improved to reduce costs
o a proper sealing method has been developed
o the electrical connection has been improved
• At least 10 thermo-cycles are possible, as has been proven in single cell experiments.
• A low weight/low volume system has been designed; 3 kg and 3.3 l for a system providing more than 280 W at EoL. The power density of stack plus reformer subsystem is better than 110 W/kg.
• The developed technology can also be applied outside aerospace in other applications, such as portable personal power supplies (chargers for telephones, laptops, radios etc), on-board power for vehicles (automotive and marine) and educational demonstrators.
• A hybrid system comprising an SOFC subsystem, a battery pack is developed capable of supplying power for a complete UAV flight.
• Various models have been developed for designing and calculating the performance of stack, and complete system. The models can be applied for the design of other hybrid systems.

0.2 Commercial Impacts
The project was set up to apply to early markets. So commercial impacts will arise only after a few years. The developed prototype modules require a subsequently iteration before market readiness will be reached. The stack stability against delamination will has to be improved and dedicated designs for specific power needs for specific UAV’s will need to be designed based upon the developed technology platform.
EADS as world leader in manufacture of air vehicles, including UAVs, already has experience in developing and commercialising technologies for aerospace applications. EADS intends to expand activities during the next years and the results obtained within this project will assist in that endeavour.
The UAV market has been grown rapidly the last years and many companies are investigating UAV’s capabilities (e.g. Amazon, Google). Since UAVs powered by a hybrid SOFC/battery power supply running on propane can increase the flight time by a factor of at least 3, there is evident benefit in this technology. Commercial feedback during dissemination activities of the project underwrite this trend.
0.2.1 International Impacts
The outcome of the project will help the partners within the project to compete on the international stage with the hybrid SOFC power systems and its components. The market for UAVs is an international one, led by the USA. EADS and Survey Copter will be able generate sales in the USA if the present project is successful. Developing countries like India also seem attractive for agricultural surveillance purposes.
0.2.2 Educational Impacts
The University of Birmingham is the UK centre for Hydrogen and Fuel Cell training and PhD students study this field in the EPSRC funded Doctoral Training Centre worth £5.5M. About half of the students work on PEM and half on SOFC projects. ZUT has been training students on fuel cell systems as well. During the project three PhD students have been working within the project (2x UoB, 1x ZUT).
0.3 Impact on Europe
The project has strengthened the European position in the field of mSOFC and mini UAVs of academia and SMEs/industry. Much knowledge has been gained requirements, designing a low weight and low volume system, manufacturing of cells and stacks and the design of a hybrid electrical system.
UoB and Adelen have gained much experience in developing mSOFCs. They will use this experience for future work demonstration and commercialisation. UOB will use its Hydrogen and Fuel Cells Centre as a platform to disseminate the promise of RTD in this area and the potential applications of the technology.
The developed catalysts by Catator will have RTD application world-wide.

0.4 Environmental and Economic Impacts
The technology developed can be used for UAVs but also for portable and small scale applications. Widespread adoption of SOFC technologies will give the environmental benefits of reduced fossil fuel usage (via increased efficiency) and reduced emissions.

List of Websites:
Contact information: HyGear, E. de Wit, +31 889494300
HyGear, R.C. Makkus, +31 889494300