Hydrogen-Electric Zero Emission Propulsion System

Project Information

HEROPS

Grant agreement ID: 101140499

DOI

10.3030/101140499

EC signature date 12 December 2023

Start date 1 January 2024

End date 31 December 2026

Funded under

• Climate, Energy and Mobility

Total cost

€ 40 398 126,75

EU contribution

€ 29 684 005,51

Coordinated by

MTU AERO ENGINES AG
Germany

Periodic Reporting for period 2 - HEROPS (Hydrogen-Electric Zero Emission Propulsion System)

Reporting period: 2024-10-01 to 2025-09-30

Summary of the context and overall objectives of the project

HEROPS -Hydrogen-Electric Zero Emission Propulsion System for Regional Aircraft

The Flying Fuel Cell (FFC) propulsion system in combination with a Liquid Hydrogen (LH2) fuel system are currently the most advanced and ambitious approaches to emission free and climate neutral flying.

The FFC electro-chemically converts LH2 into electric energy to power the aircraft propulsion. This disruptive technological approach uses the fuel cell as primary power source for the propulsion system. Close integration of the fuel cell system and the electric drive in an engine nacelle mounted under-wing ensures a compact and weight-efficient overall system. Key technical differentiation of this FFC is a configuration without use of a battery in the direct powerline between the fuel cell system and electric motor, making it a full-electric & non-hybrid power train. The topology of the electrical network and the architecture of its major components are developed jointly to achieve a high specific power of 1.5 kW/kg for the overall electric powertrain (EPT) of the multi-megawatt (MMW) system (without HFS).

This FFC system is developed for the specific requirements of aviation. This implies a different global optimum in the trade space of performance, mass and costs than in the automotive sector, which has hitherto driven R&D of fuel cell technology for mobility. Aviation-specific safety requirements call for different architectures of core components and the overall FFC system compared to the state-of-the art. A smart use and integration of aerospace-grade components enable a lean arrangement of the sub-systems in the EPT.

The FFC system implements these requirements in the design of the core components and the system architecture, providing a high-performing, safe and robust aviation-grade zero-emission propulsion system.

An aviation-native consortium of industry-leading OEM partners around MTU Aero Engines will step-wise advance the FFC propulsion system in the low temperature domain for integration into a Regional Aircraft such as an ATR. The envisaged demonstrator will incorporate the FFC architecture and targets a power level of 2-4 MW per wing with a twin-engine configuration as per today’s configuration. The FFC based full-electric propulsion architecture is in the running to become the most climate friendly state-of-the-art choice for regional aircraft by 2035.

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 project established TLARs and technical requirements for a regional aircraft with a FFC-based propulsion system. A base reference architecture was defined, including the logical architecture, func-tional decomposition, and subsystem analysis. Iterative design loops and a Design Dossier document were utilized to develop and validate the system model and interface data.

Furthermore, the test requirements specification for the MMW ground demo was initiated in collabora-tion with the consortium. The supply infrastructure for H2 and N2 was built up at MTU's Munich plant and is currently being prepared for commissioning.

Conceptual development work regarding the Electric Powertrain (EPT) was also initiated. The general gearbox, propeller, and heat exchange system (HXS) design were established.

To explore the design space and identify optimization potential, a series of trade studies were defined and established, and these studies are currently ongoing during the design loop 2, which will continue until the end of 2024.

The baseline design of the Hydrogen Fuel System (HFS) has been concluded, and the detailed design phase has been initiated with the aim of completing the Critical Design Review (CDR) for this system before the end of 2024.

Early in 2025 the preliminary design milestone has been achieved, and the baseline HEROPS MMW design has been defined. Additionally, the first aircraft impact assessment has been established.

Several component and system-level tests are planned and currently underway across various technologies, including EPT, Electrical Distribution System (EDS), HXS, Wind Tunnel Testing (WTT), and Hydrogen Fuel System (HFS), with the objective of reaching Technology Readiness Level 4 by the end of 2025.

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)

The HEROPS project aims to validate a full-electric fuel-cell-based propulsion system for hydrogen-powered aircraft. As of today, fuel cell technology in the mobility sector is driven by the automotive industry. After having achieved satisfactory performance and mass characteristics, this industry is now driving towards serialisation and minimisation of costs. To date, the application of fuel-cell tech-nology for A/C propulsion has been limited to isolated demonstrator-type applications on small CS-23 class aircraft built upon automotive technology. However, this state-of-the-art technology does not enable economically viable future aircraft in the 50-passenger class and beyond.

Aviation-grade fuel-cell propulsion technology is needed for future climate-neutral aircraft. A techno-logical leap, comparable to the electrification of the automotive sector, must reach critical performance and mass levels, justifying a different performance-vs-cost trade-off compared to the automotive sector. To this end, HEROPS develops the FFC propulsion system and its main technology bricks specifically for the application to aviation. This entails the selection of high-tech materials, but also the adaptation of the architecture of the core components to adapt to aviation-specific requirements. The aspired outcome is a FFC system with a significantly increased specific power (kW/kg) compared to the state-of-the art. Further, the system will provide the operative flexibility and robustness which is required to serve the aviation standards. For example, while automotive technology is designed with “OFF” as a safe state, aviation propulsion systems need robustness against failure modes and the possibility to continue in degraded modes to allow for a safe landing in all cases.

Besides the powertrain, HEROPS aims to demonstrate the feasibility of developing and certifying a cryogenic Hydrogen Fuel System (HFS) on an aircraft. The HFS is developed to the specific functional and safety requirements of its application to aviation and will also prepare the grounds for a future certification programme. Due to its full-electric and fuel-cell-based nature, a FFC equipped aircraft will vastly decrease GHG emissions compared to today’s combustion technology, but also compared to hybrid-electric or hydrogen-burning concepts. Carbon and NOX emissions are eliminated, and the climate-impact of possible contrails is vastly reduced thanks to the almost particle-free exhaust gas which is emitted by the fuel-cell drive, as confirmed by recent research findings in the field. Overall, the climate impact of FFC-propelled aircraft is expected to be reduced by at least 80 % compared to today’s levels.

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