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Fuel CelL HYdrogen System for AircraFt Emergency operation

Periodic Reporting for period 4 - FLHYSAFE (Fuel CelL HYdrogen System for AircraFt Emergency operation)

Reporting period: 2022-07-01 to 2023-06-30

Today, all aircraft manufacturers embrace the "More Electric Aircraft" trend, replacing traditional hydraulic and pneumatic systems with electric ones. Those offer improved performance, reliability, and cost-effectiveness. They also address the growing need for reduced fuel consumption, lower emissions, and optimized aircraft performance. Fuel cell systems are a top choice for efficient power generation in this context. The main objective of FLHYSAFE was thus to demonstrate that a cost-efficient modular FCS can replace the most critical safety systems and be used as an Emergency Power Unit aboard a commercial airplane providing enhanced safety functionalities. The project also had the ambition to virtually demonstrate that the system is able to be integrated, respecting both installation volumes and maintenance constraints, by using current aircraft designs. In order to shift from demonstrator levels to the ready-to-certify product level, it is necessary to optimise the different components of the FCS to reduce its weight, increase its lifetime, ensure its reliability, certify its safety and make its costs compatible with market requirements. FLHYSAFE proposes FC technologies using Proton Exchange Membrane FC stacks, more integrated power converters and use of next-generation aircrafts opportunities. FLHYSAFE had 3 specific objectives: 1. Design a modular FC-based EPU with a power range from 15kw to 60kw; 2. Develop and validate the FC system based EPU at TRL5-6; 3. Prepare the roadmap for exploitation.
FLHYSAFE activities started with the derivation of the EPU specifications using the performance of the existing Ram Air Turbine (RAT). A functional and safety analysis process allowed the production of a clear and consistent PID diagram. Next, the technical specification of the sub-systems was done, starting with the FCS - allowing the creation of a preliminary design integrating planned components (stack, cathode humidification system, H2 recirculation loop, sensors and actuators). Start/stop study at stack level were performed on two short stacks to define the optimised strategy to comply with the emergency application requirements. First versions of the other subsystems’ specifications (anode and cathode loops) were prepared and modelling and simulations were performed.
The preliminary design of the electrical and power management system in charge of powering all the electrical consumers (sensors, actuators and Aircraft loads) was performed through the analysis of the electrical load. The EPMS preliminary architecture and voltage buses were frozen and converters entered in detailed design phase.
This work allowed the consortium to choose between two high level architectures: an initially planned H2/air architecture or the finally chosen innovative H2/O2 architecture taking profit of next-generation aircrafts that encourages FCS engineers to use new aircraft interfaces for cooling and fuel supply - making systems much simpler that positively affects their reliability and hence makes the technology more attractive for the market.
An FC sub-system adapted to airborne applications was designed and developed. Assembly tooling adapted to FC stacks were designed and manufactured. Tests on short stack fed with O2 instead of air were performed to mitigate risks associated to oxidant choice and to optimise stack sizing.
A 0D FC model was developed and implemented to simulate the EPU system activity. This model translates stack behaviour under various operating conditions. A good fitting with experimental results was achieved. Start/stop study was conducted by applying start-up and shutdown protocol for 466 cycles, allowing conducting a mathematical analysis of the stack degradation (stack power evolution as a function of the number of start/stop cycles).
The integrated converter and its electronics, mechanics and thermics parts were designed. The electronic boards, inductors and mechanical parts were manufactured. Electronic boards were tested on a prototype version to easily adjust the HW and the SW. The assembly of the integrated version was successfully tested.
Based on the mature EPU architecture obtained during the study phases, architectures of the Low Temperature Module (FCS-a) and the FLHYSAFE demonstrator (FCS-b) were frozen. This allowed the consortium to: complete the detailed design of both systems; start the manufacturing and the assembly of the FCS-a; perform initial tests: power management table, monitoring and control, auxiliary and integrated converter tests were performed successfully; start the assembly of the FCS-b.
The tests of the sub-parts (anode, cathode, FCS-a) were conducted with mixed results. The tests done on cathode and anode loop allowed a good knowledge capitalization for the operational tests on the demonstrator. On the other hand, the stack was damaged but the control system for the operational tests could be validated and updated.
The final stack and the demonstrator were assembled, the operational tests were conducted. The demonstrator operation up to 6kW was validated despite a stack failure occurring during the test campaign. Environmental test campaign reduction scope and delay due to failure of the stack led to a short vibration test campaign with positive results.
In parallel to the technical activities, transversal activities were performed: a cost analysis ownership study concluded that the FC market in aeronautics is not mature and needs to develop to be competitive with the RAT.
The development of a Virtual Reality tool to create Assembly and Maintenance tasks and procedures through VR manipulations was achieved. The projection of the system in VR environment is functional, leading to program assembly task scenarios and perform them in VR for validation or training. The first maintenance procedures drafts were achieved.
While the scientific activities of the project were progressing, FLHYSAFE partners conducted dissemination activities to raise awareness of the project: public website and social media accounts were regularly updated to present the project events and results.
FC technology for an EPU use is challenging: regulations rules are not yet issued, there is still a risk that the architecture proposed should be adapted in the future. Project partners are involved in future discussions through WG80 EUROCAE. LT-PEM incl. FC system components for ground, automotive application is well understood but cannot be applied for aviation without further R&D efforts. RAT is a secured market by major actors offering a reliable technology for actual aircraft. Options like FC could be considered only for new H2-powered aircraft.
FLHYSAFE contributed to a better understanding of FC technology in various areas: maturity in FC stack parts manufacturing (metallic bipolar plate, sealing) enhanced by French industrial supply chain; understanding of pure O2 use in aeronautics; development of an interesting option with a DCDC to tackle integration challenges.
As next steps, after the project end, the consortium members will continue to work on:
• The weak point of the developed EPU architecture will be addressed by DLR in future projects
• A new converter receiving FC stack voltage will be studied by CEA
• INTA will develop tests facilities for anode and cathode test in altitude
• SPU will focus on FC product for non-propulsive and propulsive aeronautical application to achieve Europe aeronautical decarbonation target.
FLHYSAFE FC EPU Demo installed in INTA's altitude test chamber
FC © Safran Power Units – Remi Deligeon
Start/stop test on short stack at INTA test bench
FC Stack during mechanical tests at INTA
Cooling circuit for FCS-alpha
EPU mock-up
Fuel Cell
FC Stack during mechanical tests at INTA
FC Stack during mechanical tests at INTA
Converter and stack assembled
Integrated converter
CAD model of demo