Aviation & Maritime Systems

Flying without a CO2 footprint

Researchers: Prof. Frank Thielecke, Thimo Bielsky, Vivian Kriewall

Institute: Institut für Flugzeug-Systemtechnik (FST)

UN Sustainable Development Goals 9 und 13

Aircraft powered by hydrogen and fuel cells could help to meet climate targets. This is because they do not produce any greenhouse gases, only water is emitted.

Flying could be so nice if only it weren't for the CO2 emissions. There are many new ideas for the future on how to make flying more climate-friendly. One promising approach is to use hydrogen as a fuel instead of kerosene, as is currently the case. This would then be used to power fuel cells installed on board. Their task is to generate electrical power in the form of electricity. This works in such a way that electric motors drive propellers to generate thrust. No carbon dioxide or nitrogen oxide emissions are produced during this process or during the flight; only water is produced.

The Institute of Aircraft Systems Technology (FST) at Hamburg University of Technology is currently working on various such climate-neutral aviation research projects. In cooperation with their partners, the engineers are developing concepts and technology modules that should lead to viable hydrogen concept aircraft. Two of them are Thimo Bielsky and Vivian Kriewall. They are researching electric flight with partners Airbus and the German Aerospace Center (DLR). "We have designed the overall system architecture for a fully electric passenger aircraft and investigated and virtually tested the interaction of all relevant individual systems," says engineer Thimo Bielsky, describing the project.

Climate-neutral flying for 70 passengers

The concept aircraft itself was developed by DLR and corresponds to a regional aircraft with a design range of around 1000 nautical miles. This corresponds to 1,852 kilometers. With this range, almost all current missions can be covered by the aircraft, which can carry around 70 passengers. The concept aircraft has a total of ten drive units, known as "pods", each of which contains fuel cells, buffer batteries and the electric drive train. Each drive unit can generate an output of around 400 kilowatts. This is how much is needed to charge an electric car in three minutes for a range of 100 kilometers. Vivian Kriewall explains the main difference in the design compared to a conventional aircraft: "The hydrogen tanks are not housed in the wings, but in the rear of the aircraft. To avoid losing too much space, the fuselage of the aircraft is wider and the cabin is shorter".

Hydrogen is an ideal source of energy, but in its natural form the gas has a comparatively low density and requires a lot of volume when stored. In order to provide the required drive energy, the pressure tanks would require as much space as a second airplane fuselage if the gas were stored. The scientists are therefore using a trick and cooling the hydrogen in the concept aircraft to -253 °C as liquid hydrogen in vacuum-insulated tanks. This means that much less volume is needed.

The aircraft becomes heavier, but more efficient

"In the next step, we position the components in the aircraft and connect them to hydrogen pipes, hydraulic lines, air ducts or electrical cables," explains Thimo Bielsky. The scientists carry out various studies: For example, they can change parameters such as the number of components, their position, a pressure level or an electrical voltage level. The aim is to evaluate the influence on the systems themselves, but also on the overall aircraft. In the case of the hydrogen concept aircraft, studies were primarily carried out in relation to the energy supply in the aircraft. For example, it was investigated whether the fuel cells with the batteries in the pods are sufficient or whether systems are required to supply the on-board systems in an emergency - the hydrogen supply would fail. "Compared to a conventional aircraft, the hydrogen concept aircraft would be around five tons heavier," calculated Vivian Kriewall. "However, the overall efficiency increases by around 30 percent thanks to the fuel cells and batteries, as their efficiency is significantly higher than that of conventional engines."

Finally, the scientists still have to solve a safety problem, as hydrogen itself is highly flammable. They want to avoid routing hydrogen lines through the printed area of the cabin. In addition, the engineers at the FST Institute still have to investigate how large the distances to other systems such as the electrical or hydraulic system need to be in order to be safe. Once these tasks have been completed, the vision of electric flight, in which the aircraft glide through the air quietly and in a climate-friendly manner, can quickly become a reality.

More information

Visit the LinkedIn-Profile of the Institut für Flugzeug-Systemtechnik.

The concept aircraft has a total of ten drive units, each containing fuel cells, buffer batteries and the electric drive train (System engineering concepts and preliminary design: TUHH FST)

Making container shipping safer

Researches: Prof. Dr. Sören Ehlers, Dr. Franz von Bock und Polach

Institute for Ship Structural Design and Analysis

Container ships that lose some of their cargo not only suffer an economic loss, every accident leads to major ecological damage. The "TopTier" project is investigating how cargoes can be better protected in extreme weather.

Anyone who has ever had the chance to look at a loaded container ship up close is probably impressed by its size. Up to 25,000 of these steel boxes are stacked on deck, right up to the sky. Most of them are transported across the oceans without incident. But in heavy seas, cargo can slip and containers can go overboard. They are measured in TEUs, where a TEU is equivalent to a 20-foot container - that is, about seven meters long. The World Shipping Council, an advocacy group for shipping companies, reported a loss of 1,400 TEUs in 2020. But the numbers are rising, with more than 2,500 containers going overboard from October 2020 to March 2021 alone. In November 2020, the container ship ONE Apus alone lost 1,816 containers, and in January 2021, Maersk Essen complained of a loss of 750 of the metal boxes. This not only leads to ecological and economic damage, containers floating in the water additionally pose a collision hazard. With its Institute for Design and Strength of Ships, TU Hamburg is involved in the industry project "TopTier" with tests. The aim of the project is to reduce the probability of containers being lost at sea and to identify improvements in ship safety for the coming decade.

Shipping: discussion on safety and environmental impact.

"Container shipping is essential to the modern global economy. Although accident rates are extremely low in percentage terms, the absolute numbers are too high. At least 1,000 containers are lost at sea every year, and many people are injured during handling operations," explains Prof. Sören Ehlers, who is responsible for the TU project. In the past, there has already been serious damage to the coastal marine environment. This has led to discussions among the public and politicians about the safety and environmental impact of modern container ships - so that both politicians and industry are now being called upon to respond to potential problems in container securing.

But why is it so difficult to adequately secure containers on ships in the first place? The answer lies in the construction of the ships. They have become larger and larger in recent years to accommodate more cargo. Experience with new ship sizes, their operating conditions and loading mechanisms is therefore still limited, and in the case of extreme events such as particularly bad weather at sea, these uncertainties increase. "Current limits do not cover all factors involved in the newest classes of ultra-large container ships. A better understanding of these conditions and mechanisms of action is therefore necessary," says shipbuilding expert Ehlers.

Measuring container ship loadings and wave motions

The TopTier project is divided into several tasks. The first is to identify the most important aspects of cargo stowage and securing on container ships identified in 2020 and to verify them with the help of interviews and questionnaires with, for example, shipping companies, ship crews and terminal workers. "We then focus on how to deal with current cargo securing practices. To this end, project coordinator MARIN has tested ships in the wave channel and measured ship movements. From this data, we can deduce how size, cargo and loading condition react under certain wave conditions," says Prof. Ehlers, explaining the individual criteria. In the further course of the project, things will get particularly exciting: The researchers want to find out how it is that containers slip. To do this, they are studying the ship's movements; in particular, horizontal bending and torsion, a helical twist. These effects are tested through a combination of measurements, model tests and numerical studies. Finally, the behavior of the ship's crews also plays a role. Ideally, they should be able to actively prevent incidents. The results of the project will be passed on to the relevant shipping authorities, where they will be implemented for all concerned - so that a level and safe playing field continues to apply both at sea and on land.

The international project is led by the Dutch research institute MARIN. For more information, visit https://www.marin.nl/en/jips/toptier.

Goal: climate-neutral shipping


Researcher             Thilo Jürgens-Tatje

Duration                 10-2018 – 03-2022

Institute                  Marine Engineering

School of Studies    Mechanical Engineering (M)

Alternative fuels such as green methanol are CO2-neutral and can ensure that climate targets are met in shipping. A TU joint project is researching their practicality in detail.

Whether tanker, container ship or cruise liner: Up to now, commercial shipping has been using fossil and mostly polluted heavy fuel oil. This damages the environment and, above all, the climate. The use of exhaust gas purification systems such as scrubbers or catalytic converters can already effectively minimize sulfur, nitrogen oxide or soot emissions on board ships. In order to achieve the climate targets in the transport sector, climate-damaging emissions such as CO2 must also be significantly reduced. Climate-neutral energy sources are therefore needed on ships. These energy sources could be created using power-to-X processes. These are ways of producing various synthetic fuels that are CO2-neutral in the overall balance because the carbon was previously removed from the atmosphere for synthesis. In the E2-Fuels joint research project, the marine engineering group is investigating the use of methanol and oxymethylene ether (OME) as maritime fuels. The focus is on the port infrastructure and bunker interface required on land, as well as on the fuel system on board.

Renewable and synthetic fuel

Thilo Jürgens-Tatje is in charge of the E2-Fuels project in marine engineering. He would like to influence the moving away from diesel or fossil gas and toward climate-neutral propulsion fuels that are suitable for practical use on board. "Electrification as with cars is often not possible; corresponding batteries would be too large and too heavy. The only exceptions could be smaller ferries used for short distances. Therefore, you need hydrogen as a feedstock, which is generated from renewable electricity from wind and sun," the scientist explains. But the use of hydrogen as a marine fuel entails some disadvantages. For example, extreme pressures or temperatures close to absolute zero of minus 273 degrees are required for storage. Therefore, a conversion step to a mobile synthetic fuel is still necessary. This process is called power-to-X. Methanol has already been used on a small scale as a marine fuel for some time, for example, on tankers or ferries. It is a liquid alcohol that can be transported easily. And it has another positive property: In the event of an accident, there is no need to fear a dangerous oil slick; the methanol simply dissolves in the water. It's like tipping a bottle of schnapps into a full bathtub. But there is, of course, a catch: CO2 is needed for production, and this is also released again when the methanol is burned in the engine. In principle, this is not a problem; cement plants or waste incineration plants emit a lot of the unloved gas anyway. Jürgens-Tatje's goal, however, is to make the entire process carbon-neutral. "You could use CO2 from biogas plants. So there would be nothing standing in the way of the closed-loop system.

The big challenge is to produce enough methanol from green hydrogen and green electricity, respectively. To run the whole process economically, people are now relying on hydrogen produced near the equator with the help of solar energy and brought to us by ship," explains the shipbuilder. "Electricity is simply too expensive here in the long term. Nevertheless, we need pilot plants in Europe, too, to solve the chicken-and-egg problem."

But how does the fuel get on board? The TU scientists have developed a solution for that, too: "Refueling terminals where container or cruise ships pick up their fuel are not practical. It simply takes too long. So they investigated the current refueling system, in which so-called bunker ships ensure that the required diesel fuels are transported from large tank facilities on land to the respective ships. The actual refueling then takes place "ship-to-ship" while the ship is taking on or delivering cargo. "Our investigations have shown that the conversion of a conventional bunker vessel is technically and economically feasible. There are also areas in the port that are perfectly suitable for a tank farm on land," Jürgens-Tatje said.

The trick with ignition

Today's diesel engines have to be adapted for the use of methanol. That's because methanol must be ignited like gasoline in order to burn. Unlike diesel, which, if appropriately compressed, will self-ignite. "In large marine engines, however, ignition cannot take place via a spark plug as in a motor vehicle engine. Instead, a small amount of diesel is injected at the right moment with an injector to ignite the methanol," says supervisor Jürgens-Tatje. Project partner MAN has tested an injector designed for this purpose on a test engine. "This is a breakthrough. Soon, conventional diesel engines can be converted relatively easily so that they can also run on methanol," explains the TU scientist. And so methanol could become established as an energy source. The Danish shipping company Maersk is leading the way: It has already ordered 12 new container ships powered by methanol.

Thilo Jürgens-Tatje is a member of the marine engineering group and is responsible for the theory and practice of the E2Fuels project.