Development and optimisation of a dedicated Fuel Cells for Aviation: from dedicated stack (100s kW) up to full system (MWs)

The technology (Proton Exchange Membrane Fuel Cell) that is emerging from the automotive industry through car manufacturers is of interest for aeronautic industry, but some issues are still to be solved (hydrogen storage and distribution from the tank to the fuel cell system are not considered here)

• The power of the fuel cell systems coming from the automotive industry is usually limited roughly to 100kW. Aviation needs are more in the range of 1 to 5MW depending on the size of the aircraft and/or the systems to supply with power (propulsive or non-propulsive). Development of 250 kW FC stack and scalability of FC system and components for an at least 1.5 MW module seems thus compulsory in order to allow aircraft application. This target is moreover clearly defined in the Clean Aviation SRIA;
• The stacks available today are not adapted to the environment in which they will have to operate: temperature ISA-35, pressure 0,2 bar (45 kft), vibrations, etc;
• The requested power is not achievable with only one stack. The following should be defined:
  • • The optimal size of the stack;
    • The architecture of multi-stack systems.
• The cost of the technology needs to be reduced. Sizing a unitary stack of a reasonable amount of power will ease its integration in different size of aircraft and for propulsive and non-propulsive systems. This will increase the numbers and ease cost reduction;
• The lifetime of the fuel cells should be increased;
• Safety issues shall be considered right from the start. The means of compliance in order to answer to qualification/certification needs are not available. The certifications rules should be created/adapted.

Proposals should target a fuel cell system with a power density > 1.5kW/kg at a power level of at least 1 MW. The goal is to bring the technologies and sub systems to TRL5 at the end of the project, with lab and ground tests in a relevant environment.

This topic is crucial regarding the commercialisation of FC Systems in aviation.

The integration of the full system into the aircraft needs to be considered and anticipated but is not the key focus and will be dealt with in a separated Work Programme. In the frame of Clean Aviation Partnership, an open call is expected to be launched to cover system integration and demonstrations.

Proposals should tackle the following aspects:

Requirements & specification

• Define a system compatible with aircraft (A/C) environment and constraints (safety, durability, availability, temperature, pressure);
• Define architecture to optimise weight and adequation to safety requirements. A system requirement and a high-level architecture optimum should be defined and agreed early in the project;
• Derive necessary technological bricks to be matured up to TRL5.

Fuel cell stack subsystem

• Increase the power density of the stack, by optimising designs through several means, for example but not exhaustive: lightweight metal substrates, high performance Membrane Electrode Assembly (MEA)/flow field combination, optimised stack compression system;
• Define and design stack architectures (i.e.: liquid cooled / 2-phase cooled). Separate paths may be explored;
• Increase the operating temperature of the stack and its capability to support larger inlet/outlet cooling temperature ranges, without compromising its lifetime;
• Analyse the robustness of the fuel cell stack to contaminants or other pollution source of the membrane;
• Reduce pressure losses over the stack, especially on the cathode, to balance stack performance versus system performance.
• The stack to be developed under this topic should be compatible with the requirements of the Clean Aviation Partnership SRIA in order to be implemented in ground and in-flight demonstrations scheduled within Clean Aviation partnership.

Balance of Plant (BoP) subsystem

• Define and resize anode and cathode BoP for stack regulation. BoP architectures may differ depending on stack architecture;
• Define a lightweight and robust stack monitoring system, easy to install and repair.

Besides, great care should be taken to the fuel cell interfaces, which will impact the trade off and overall system benefits:

Thermal management subsystem

• Fuel cell stack thermal management is key and should be analysed.
• Proposals will also have to cope with preliminary design of stack heat management. The realisation of fuel cell system driven aviation belongs from the maturity and understanding of fuel cell system components and behaviour in aircraft environment. Based on stack developments scheduled in the first phase of the project, a focus on fuel cell system behaviour at continuous (more than 15 minutes) max power operation is strongly encouraged, so that dedicated heat management bricks will have to be developed. The technology drivers, components and behaviours which will be functionally upgraded can be (non exhaustive list): cathode air supply, intercoolers HEX, cathode humidifier, anode recirculation, relative humidity sensors, stack cooling pump, stack cathode and cooling flow pressure drop. Major focus will be (on at least a 300kW electric FC unit) the integration, debug and test of a FC module at max constant cooling temperature under A/C conditions. An additional focus will be the thermal optimisation of the cooling system and controls during major load changes.

Air supply subsystem

• Define the air supply subsystem adapted to high altitude conditions (high compression rate and efficiency) and propose potential technological bricks in order to ensure this function: air inlet, filter, compressor and turbine, intercooler, humidification system, cathode recirculation, water separation, water management, air exhaust, piping and tubing, valves, temperature management, flow measurement and associated control.

Other hydrogen sub systems (storage, distribution) are outside of the scope of this topic. Proposals may include activity for the test bed development for FC testing in simulated A/C applications, and the development of relevant test protocols for performance and lifetime assessment for A/C load and operating environment profiles.

Activities developing test protocols and procedures for the performance and durability assessment of electrolysers and fuel cell components proposals should foresee a collaboration mechanism with JRC (see section 2.2.4.3 ""Collaboration with JRC""), in order to support EU-wide harmonisation. Test activities should adopt the already published EU harmonised testing protocols[[https://www.clean-hydrogen.europa.eu/knowledge-management/collaboration-jrc-0_en]] to benchmark performance and quantify progress at programme level.

Activities are expected to start at TRL 4 and achieve TRL 5-6 by the end of the project.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2022 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2021–2022 which apply mutatis mutandis.