Development of specific aviation cryogenic storage system with a gauging, fuel metering, heat management and monitoring system
Proposals should focus on the development of an aerospace applicable liquid hydrogen storage system. There are various thermal, mechanical, safety and system integration challenges associated with this. Compared to kerosene in the wing, hydrogen storage leads to additional mass for the aircraft and requires additional space (LH2 has 4 times the volume compared to kerosene at iso-energy content). Therefore it has a significant impact on the overall energy required for a mission due to both weight and volume with drag penalty.
Today’s hydrogen tanks for storing liquid hydrogen in aerospace are mostly made of metal. For space application this solution is still valid, because of power available, non-reuse and costs. But having in mind commercial aviation, the focus should be on enhancing the reliability of the metal tank and piping performance while designing a LH2 storage system made of light carbon fibre reinforced materials. Using these components, a significantly improved gravimetric index for the whole storage system can be achieved. The drawback of using these materials is that the laminate quality or laminate architecture are of particular importance for permeability. Different test specimens, different semi-finished products made of glass, carbon, fibres with polymer or metal matrix, different additives, liners and architectures as well as protective coatings have to be considered. In addition, a selection of adhesives has to be made for use in cryogenic environments.
Besides the material selection and definition and control of the manufacturing process other aspects of the function and safe operation of a liquid hydrogen storage should be taken into account. The pressure and temperature of the LH2 should be monitored to validate feed and fuel gauging functions under flight accelerations. The analysis of dynamic loads as a result of fuel sloshing should be addressed numerically and experimentally, as well as the pressure development in the tank due to the interaction of the sloshing hydrogen and the thermodynamic environment in the tank. The design solution should address the changing pressure by either active or passive means (e.g. active pressurisation control or passive anti-sloshing devices), to ensure safe operation of the engine feed systems.
A hydrogen content control and gauging system is required to provide accurate data on mission fuel throughout the flight, minimising unusable fuel and meeting all applicable airworthiness regulations. The structural integrity of the hydrogen tank has to be monitored by structural health monitoring (SHM), which can detect and locate damage. The system shall manage both normal and failed system states safely. Wireless and low energy systems shall be investigated to maximise safety and maintainability. The tank should have means to safely manage overpressure cases by a venting system to minimise risk of ignition and the impacts of cryogenic temperatures.
For operation the LH2 evaporation and gas warm-up requires a considerable amount of energy. It has to be investigated how the thermal load will be injected into the storage with a focus on transient behaviour and start-up procedures. The hydrogen fuel tank should be able to facilitate applications of hydrogen burn engines as well as hydrogen fuel cell-based powertrains with minor adaptations only, permitting for either centralised boil off or distributed boil off management.
Considerations to the refuelling interface should be given, but the interface it-self is out of scope of this topic. Boundary conditions for this refuelling consideration include:
- Aircraft refuelling at a rate of approximately 5 tonnes/hour with means to refuel a cold or a warm vessel
- The cryogenic fuel will be distributed from one, or multiple tanks in the aircraft to an end user system.
- A standard coupling as an interface to refill aligned or adapted as well with other mobility sectors that allows a safe, reliable operation by the ground staff.
The gained experiences on the two storage demonstrators will be used in phase 2 (2026-2030) to obtain and define the certification regulation of commercial aviation hydrogen storages. Furthermore, in phase 2 (2026-2030) larger tanks have to be developed to become flight worthy.
Activities are expected to start at TRL 1 achieve and TRL 3 by the end of the project (CFRP[[Carbon Fibre Reinforced Polymer]]).
Activities are expected to start at TRL 2 achieve TRL 4 by the end of the project (system).
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.