Novel recuperation system to maximize exergy from anergy for fuel cell powered geared electric aircraft propulsion system.

Project Information

exFan

Grant agreement ID: 101138184

DOI

10.3030/101138184

EC signature date 16 November 2023

Start date 1 December 2023

End date 30 November 2027

Funded under

• Climate, Energy and Mobility

Total cost

€ 3 984 082,50

EU contribution

€ 3 984 082,50

Coordinated by

FUNDACION CIDETEC
Spain

Periodic Reporting for period 1 - exFan (Novel recuperation system to maximize exergy from anergy for fuel cell powered geared electric aircraft propulsion system.)

Reporting period: 2023-12-01 to 2025-05-31

Summary of the context and overall objectives of the project

To achieve climate neutrality in aviation by 2050, hydrogen-electric aircraft propulsion holds the unique potential for zero in-flight CO2 emissions. To make hydrogen-electric flight feasible on a large scale, several challenges must be addressed. One of the main challenges is the thermal management and heat rejection of fuel cells. For each watt of electricity produced by a fuel cell, approximately one watt of waste heat is generated. This substantial amount of heat must be removed from the fuel cell and holds great potential for recuperation. The exFan project aims to apply the ram-jet effect, also known as the “Meredith Effect,” to generate thrust from waste heat. This is achieved by integrating a ducted heat exchanger within the nacelle of the propulsion system. This heat exchanger will enable high heat rejection and low drag through a lightweight bionic design and a surface coating that resists particle accumulation, corrosion, and erosion. A new thermal management system concept will be developed to optimize heat quality and manage heat sources and sinks within the propulsion system, enabling operation even under extreme ambient temperatures. The exFan system will be integrated into a geared electric fan propulsion system of megawatt class, powered by hydrogen fuel cell technology. A simulation model will be created to optimize operating parameters. Initial functional lab-scale tests of exFan will serve to verify the potential for heat recuperation.
The breakthrough innovations proposed in exFan will:

i) allow European aircraft manufacturers to reduce operational costs,
ii) enable the European aeronautics industry to maintain global competitiveness and leadership, and
iii) make a significant contribution toward CO2- and NOₓ-emission-free aircraft.

exFan brings together multidisciplinary experts from academia, aeronautical associations, and industry, supported by a selected technical advisory board. exFan will maintain close contact with Clean Aviation and Clean Hydrogen to create synergies and accelerate development.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The technical work of exFan started out with investigating the aircraft boundary conditions and the hybrid energy system with the goal of identifying favourable operating conditions, synergies and advantageous aircraft integration as well as providing a concept of the hybrid energy system to reduce heat generation and system weight.
For this, an environmental model that represents the ambient conditions at different altitudes and climatic conditions as well as a rough sizing model for all components of the propulsion system were developed. Different aircraft configurations were investigated and a baseline configuration was chosen. A parametric analysis was performed that set the optimum operating conditions for the exFan. Using the sizing models for all components and the aircraft itself, a baseline aircraft with corresponding system topology layout and system architecture was defined. In parallel, the requirements for the exFan concept and baseline cases for the life-cycle assessment of the exFan were set-up.
As the aircraft level was defined, the project moved on to develop a concept for the exFan in a multidisciplinary approach: Knowledge on the interaction of exFan components was gathered and concepts for the electric machine, gearbox, fan, heat propulsor, thermal management and energy system were set up with the goal of reducing weight in respect to the whole aircraft. At this point, a flexible aircraft model had been developed, that is able to give feedback on concept decisions with conflicting optimization criteria (e.g. increasing fuel cell efficiency vs. reducing fuel cell weight). For the exFan concept, mass, build volume and performance over a design mission was defined for each component and a 3D representation of the concept was developed to demonstrate component assembly and envisioned aircraft integration. Strategies to achieve take-off during hot ambient conditions were developed.
To further improve heat exchanger efficiency and durability, several surface treatment techniques are being evaluated, such as chemical polishing and electroless nickel-phosphorus (NiP) coatings. These methods are being tested on complex geometries manufactured via additive manufacturing, including internal channel structures. The treatments aim to enhance corrosion and fouling resistance, improve heat transfer, and reduce aerodynamic drag, all contributing to the overall performance and longevity of the propulsion system.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

exFan will move beyond the state of the art by:
• Allowing >1MW heat rejection during hot day take-off by incorporating an innovative compact, HX structure with 20% increased surface at similar drag penalty as a state-of- the-art conventional aircraft HX
• Using the ram-jet/Meredith effect to achieve up to 10% net thrust gain.
• FInding technological solutions to raise the quality of heat (= coolant temperature at HX) and thus reduce the size of the thermal management system, increase the capability for recuperation and enable hot-day take-off.
• Investigating key enabling technologies for high-RPM geared drivetrains such as high strength rotors and highly efficient cooling system with the goal of progressing specific continuous power from currently 5kW/kg to 15kW/kg and efficiency up to 97%.
Develop a TRL3 heat exchanger coating to reduce particle accumulation by 60%

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