Hydrogen-electric propulsion systems for use in aviation
Ulm University receives 1.8 million euros from EnaBle research network

Ulm University

The aim of the research network EnaBle is to make hybrid-electric flying more efficient and safer, and thus commercially viable. The research network is receiving funding in the amount of 8 million euros from the Federal Ministry for Economic Affairs and Energy. The focus is on the development and optimisation of a highly innovative hybrid propulsion system for air traffic that combines fuel cells and battery systems. At the heart of the project is a 250 kW electric propulsion chain module, which uses fuel cells fed by compressed air. The project is being managed by Diehl Aerospace. Ulm University is also involved with sub-projects, for which it is receiving 1.8 million euros in funding.

In the future, air traffic will need to become cleaner and quieter. Achieving this goal requires highly innovative solutions for environmentally friendly aircraft engines. Hybrid systems that combine fuel cells and batteries are particularly promising for this purpose. Not only do they achieve a significantly higher cruising range than that of a purely electric aircraft, but they also offer the technological potential for upscaling to larger performance classes. In order to expedite progress toward industrial production and commercial use of this advanced technology, the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie,  BMWi) is providing 8 million euros in funding for the EnaBle research network. Participants of the consortium include Diehl Aerospace and MTU Aero Engines, two leading industrial companies from the aerospace sector, as well as the German Aerospace Centre (Deutsches Zentrum für Lüft und Raumfahrt, DLR), the DRL spin-off H2Fly and Ulm University.

“We are working together to develop a hybrid electric propulsion system consisting of a fuel cell, a battery, power electronics and a power management system. The concrete objective that we hope to achieve is the industrial application for light motorised aircrafts with up to 19 seats in the near future,” explains Ronny A Knepple. The engineer is responsible for the division of energy systems at Diehl Aerospace. The company, which is coordinating the EnaBle research network, is a technological leader for avionics systems and a specialist for cockpit equipment.

How do hybrid systems like this actually work?

“The fuel cell produces electricity out of hydrogen, securing the energy base for the propeller engine. Lithium-ion batteries provide additional power during take-off or ascent, which is necessary in order to reach cruising altitude,” says Dr Caroline Willich, a scientist from the Institute of Energy Conversion and Storage at Ulm University. The engineer oversees the sub-projects in Ulm in cooperation with Dr Christiane Bauer, a fellow colleague from the institute. Among other things, the air supply module for the fuel cell will be developed at Ulm University. “The fuel cells that are used here operate with compressed air. The added pressure is what makes the fuel cells more efficient and enables higher output. This is of particular interest with respect to aircrafts, as they travel at high altitudes and thus in the negative pressure range,” Willich explains.

Ulm is also responsible for the development and optimisation of the power management system. This system must precisely, promptly and reliably ensure that the battery provides additional energy for the engine when a high level of energy is required and that it can then be recharged during flight. The power management system should be able to react precisely to the requirements of different flight profiles. A special unique feature of the fuel cell research site in Ulm is the test stand, which is integrated into an air-conditioned negative pressure chamber. In this way, complete propulsion chain systems can be characterised and tested under realistic, flight-relevant conditions.

Modularisation increases scalability and facilitates maintenance and repair

A central aspect in the development of a propulsion chain is the modularisation. The network partners hope to increase the scalability of the system, on the one hand, which is ultimately essential if a prototype is to go into serial production. On the other hand, a modular development concept also facilitates error detection and correction and thus makes maintenance and repair easier, which in turn increases safety. To make this possible, hardware and software need to be optimally aligned.

What is critical for the success of the project is the generic computer platform, which is to be developed and used within the scope of the EnaBle project, including its comprehensive control and regulation algorithms, which will ensure efficient and smooth operation of the propulsion chain. Diehl Aerospace is providing so-called Integrated Modular Avionics (IMA) for this purpose. The acronym refers to a modular computer-aided electronic unit consisting of standardised components and interfaces, which ensures that the various systems in the aircraft are able to communicate with each other.

The Institute of Technical Thermodynamics at the DLR is focusing in particular on the development of the fuel cell and battery system. At Ulm University – as described above – the researchers are primarily focusing on the air supply module for the compressed air fuel cell, the reliable performance management and the testing of the new hybrid complete propulsion train in the University’s own test station with an air-conditioned negative pressure chamber. MTU Aero Engines, Germany’s leading engine manufacturer, is working on the overall integration of the development concept for the aircrafts in the 19- to 80-seat class. The role of the DLR spin-off H2Fly in EnaBle is primarily to clarify safety requirements and certification issues.

Germany to become technological leader in the field of hybrid systems

“Industrial companies, research institutes and spin-offs are working hand in hand in EnaBle. Ultimately, the objective is to build up comprehensive system competence for fuel cell-battery hybrids, which will help strengthen Germany’s position as a leader in the field of technology and to create new jobs,” the project partners relate. But Ulm University and its students also benefit from this industrially oriented joint project. “EnaBle gives our young scientists the chance to conduct application-oriented research in a highly innovative environment. Our engineers learn to work in accordance with standards and quality guidelines, to prepare the industrialisation of products and, at the same time, advance future technologies,” Dr Christiane Bauer remarks.


Text and mediacontact: Andrea Weber-Tuckermann

A glimpse inside the test stand
A glimpse inside the test stand: Here electronic components of a performance management system for hybrid systems can be seen as it undergoes testing (Photo: Elvira Eberhardt / Uni Ulm)
test stand
The test stand is located in a fully air-conditioned negative pressure chamber. Here, hybrid propulsion systems are also tested under realistic conditions. After all, temperature and air pressure can vary considerably depending on cruising altitude (Photo: Elvira Eberhardt / Uni Ulm)
Scientists from the Institute of Energy Conversion and Storage
Scientists from the Institute of Energy Conversion and Storage follow camera images from inside the test stand on the monitor (Photo: Elvira Eberhardt / Uni Ulm)
Preparation of a fuel cell
The fuel cell must be prepared before it can be tested in the air-conditioned negative pressure chamber. Dr Christiane Bauer (left) and Dr Caroline Willich during set-up (Photo: Elvira Eberhardt / Uni Ulm)
Dr Caroline Willich (left) with Dr Christiane Bauer.
Dr Caroline Willich (left) with Dr Christiane Bauer. The engineers are responsible for Ulm University’s sub-project within the EnaBle network (Photo: Elvira Eberhardt)