Project Liquid H2

The next chapter in hydrogen-powered aviation

Discover our team
Discover our team

Our Mission

We bring liquid hydrogen into the air and prove with Liquid H2 that emission free aviation is the future.

Our solution

After our successes with battery powered and gaseous-hydrogen propulsion systems, we take the next logical step: developing a propulsion system with liquid hydrogen. The energy density of liquid hydrogen is about three times as high as that of conventional aircraft fuels like kerosene, and therefore makes considerably longer flight routes possible.

Our approach

We focus on the development of the system as a whole rather than on individual components. We take existing, proved components and rearrange them in a way that hasn't been done by anybody before. Not only the system design but also the structural integration into our carrier plane as well as safety are in the centre of our attention.

Crossing the English Channel

With our project Liquid H2 we aim to be the first hydrogen powered aircraft to cross the English Channel, with one stopover in Paris. This flight will mark an important milestone in emission free aviation, and will demonstrate the reach and practicability of our hydrogen propulsion system. We prove that sustainable flight with hydrogen is ready to shape the aviation of tomorrow.

Range

500

km

LH2 temperature

-253

°C

Hydrogen capacity

~10

kg

Technologies of the future

Tank

Lightweight design & energy density

For the propulsion system, we rely on liquid hydrogen as the main energy source. Although this must be stored at -253 °C, it offers significant advantages: its energy density is almost 70 per cent higher than that of gaseous hydrogen in modern 700-bar pressure tanks and also allows storage at a much lower pressure. Compared with kerosene, the energy density per kilogramme is actually three times higher. To minimise weight as much as possible at these extreme storage temperatures, we manufacture both the inner and outer tanks from aluminium rather than steel. A single tank holds 5 kilogrammes of fuel, meaning that the entire system weighs just under 40 kilogrammes when fully fuelled.

Tank

Insulation & Tank Suspension

To insulate the liquid hydrogen, we use a vacuum and reflective foils (MLI) in the tank’s annulus. At -253°C, the aluminium inner tank contracts by several millimetres. To prevent material stresses and minimise heat transfer, we have developed a flexible suspension system comprising pre-tensioned cables and a spring-mounted pin. This mechanism compensates for the contraction and keeps the tank securely in position, even during flight manoeuvres and landings.

Tank

Structural Mechanics (Buckling of the external tank)

The outer tank of our system fulfils an essential function: it encloses the inner tank and maintains a high vacuum. This vacuum is necessary to enable the Multi-Layer Insulation (MLI) film to effectively shield against incoming thermal radiation.

However, the vacuum inside causes the ambient atmospheric pressure to bear down on the outer shell. This creates the risk of so-called buckling (the structure becoming dented). The image shows a structural simulation of this phenomenon: red areas indicate zones with a high potential for deformation, whilst blue zones remain stable. The spatial displacement has been greatly exaggerated for clarity. Using the insights gained from these simulations, we can iteratively refine the design and add targeted stiffeners to the shell to reliably prevent buckling.

Tank

Vacuum box

Our vacuum box contains all the valves required for filling and emptying the tank. Thanks to the vacuum, there is virtually no heat transfer into the pipework, which minimises evaporation losses. Given the extremely low temperatures in the pipework, the outside air would begin to condense or even freeze if it weren’t for the vacuum.

Heat exchanger

Heat exchanger

To bring the cryogenic hydrogen up to the optimum operating temperature before it enters the fuel cell, we use a heat exchanger developed in-house, which is manufactured using 3D metal printing. This utilises the waste heat generated by the fuel cell. Aluminium is used as the material: compared to steel, it has significantly better thermal conductivity, which makes heat exchange much more efficient. Through comprehensive thermal simulations and iterative design, we also ensure that the hydrogen is brought to the ideal temperature, whilst reliably preventing the coolant from freezing.

Testing

Test bench – infrastructure

Developing our own liquid hydrogen tanks requires a bespoke test infrastructure. The tanks can be put through comprehensive testing on our test rig. They are tested for everything from leak and pressure tests to tests involving liquid hydrogen. Another key component is the complex refuelling procedure: to prevent unnecessary evaporation of liquid hydrogen, the tanks are first pre-cooled with liquid nitrogen before the final filling with liquid hydrogen takes place. These and other comprehensive test series guarantee the highest level of safety for subsequent use.

 

Testing

Test bench – infrastructure

In order to test a liquid hydrogen system, we are constructing a new test rig which will expand the capabilities of our existing test infrastructure. This includes the necessary technology to liquefy and store hydrogen in its liquid state, as well as a piping system to fill the tank with liquid nitrogen and hydrogen. This piping system also includes a vent stack: This serves as a controlled vent to the atmosphere and ensures that excess hydrogen – for example, due to natural evaporation (boil-off) or when flushing the pipes – is vented at a safe level at all times. A new control cabinet is also being installed for the test site to handle the power supply and control of the system.

Antriebsstrang

Testing

The fuel cell team has developed a new test rig. The aim was to develop a modular system that enables rapid prototyping whilst supporting ongoing development. The test rig allows the fuel cell itself, as well as all associated auxiliary components, to be tested. In the long term, the design provides the flexibility to adapt, expand and further develop the system in any direction.

 

Antriebsstrang

Compressor

The new compressor in our system features an integrated expansion turbine, which enables partial energy recovery from the fuel cell’s exhaust gas. At the system’s highest setpoints, this results in energy savings of up to 20 per cent compared with the previous compressor without an expansion turbine. The main function of the compressor is to supply the fuel cell with compressed air, thereby enabling the electrochemical reaction between oxygen and hydrogen.

Antriebsstrang

Fuel Cell Control Unit (FCCU)

Our system introduces a new control architecture based on model-based control. This approach enables centralised control of the entire system. Using digital system models, we can simulate the entire fuel cell system and optimise the control parameters in advance. This significantly reduces the amount of testing required and speeds up the commissioning of the system.

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