In the engine rooms of future ships

Researchers: Prof. Friedrich Wirz, Dr Jasmin Bullermann, Anna Del Monego

When people think of climate-neutral shipping, they usually picture huge container ships sailing the world’s oceans on green fuels rather than heavy fuel oil. The real challenge of achieving this begins early on – in small glass vials containing yellow, red or dark brown liquids, deep inside a ship’s engine. In the laboratory of the Marine Engineering Working Group (ASM) at Hamburg University of Technology, rows upon rows of precisely such vials are lined up. Each of these fuel samples comes from a different port around the world. Some are the colour of apple juice, others resemble dark tea.

International shipping is in the midst of a major technological upheaval. The climate targets set by the International Maritime Organization (IMO) and the European FuelEU Maritime Regulation require greenhouse gas emissions to be drastically reduced. Even today, fuels containing CO₂-neutral components must be used in European waters, and by 2050 this proportion is set to rise to 100 per cent. But what simply sounds like a switch is turning out to be a highly complex puzzle. “Biofuels can be produced from a wide variety of raw materials: used cooking oils, animal fats such as boiled cowhides, wood waste or other biogenic residues, such as cashew nut shells or sewage sludge. Synthetic fuels produced using green hydrogen are also increasingly being added to the mix,” explains Dr Jasmin Bullermann, a chemist in Prof. Friedrich Wirz’s research group.

When the fuel tank becomes a surprise bag

Together with the Hamburg-based shipping company Auerbach, the Technical University of Hamburg is investigating, as part of the “Bio-Tank” research project, which biofuels are best suited to real-world shipping operations. The shipping company was only founded in 2015 and has set itself the goal of making global trade more sustainable. It does not operate scheduled shipping services and is therefore unable to plan where its ships can be refuelled. As a rule, refuelling takes place wherever the ships happen to be and where fuel is currently available – in Rotterdam just as much as in Singapore or South America. This means that a wide variety of fuel mixtures with different biogenic content come into contact with one another in the tank. Often, residual quantities from previous bunkering operations are also still present in the system. So far, no one knows exactly what happens chemically when all these fuels mix. “In the worst-case scenario, such mixtures can damage the propulsion engines or even lead to engine failure,” says Bullermann.

That is why the shipping company collects fuel samples from around the world, which are then analysed at the Technical University of Hamburg. In the laboratory, chemist Bullermann dips small rods made of shipbuilding steel into the various liquids. After a while, they look completely different: some still gleam silvery as before, whilst others are already significantly corroded or show the first signs of rust. But corrosion is only part of the story. The researchers are also investigating how the fuels change over time, whether different blends are compatible with one another, how they react with materials, and whether they form stable mixtures. Finally, a so-called droplet test reveals whether a fuel remains homogeneous or whether its components separate from one another. Ultimately, the question is not only how climate-friendly a fuel is, but also whether it is reliable.

It’s not just the fuel that matters

But even if a new fuel leaves the fuel tank unscathed, the work is far from over. Combustion behaviour, temperatures and chemical processes sometimes differ significantly from those of conventional fossil fuels. Another component is crucial for the smooth operation of marine engines: lubricating oil.

In the “FuelOptimOT” research project, the research group is therefore investigating the interaction between fuel (methanol) and lubrication in modern marine engines. “In concrete terms, you can imagine oil droplets flying around in the combustion chamber,” explains Prof. Friedrich Wirz. What sounds harmless can have significant consequences. If lubricating oil enters the combustion chamber, it affects the combustion process, particularly in engines fuelled by methanol. “This can lead to unwanted spontaneous ignition, which impairs the engine’s efficiency and service life.”

For this reason, the findings obtained in the laboratory are subsequently tested on two engine test benches under conditions that closely resemble real-world operation. This allows chemical and physical properties to be linked to the actual behaviour within the engine and assessed holistically. The researchers are also investigating, using specially equipped marine engines, how oil transport within the engine can be specifically controlled. Using laser-induced fluorescence (LIF) measurements and simulation models, the piston assembly is optimised so that less lubricating oil enters the combustion chamber, thereby reducing combustion anomalies. The aim is not only to use climate-friendly fuels, but also to exploit their potential as efficiently as possible.

Many pieces of the jigsaw for the shipping of the future

These two research projects exemplify why climate-neutral shipping is about far more than simply searching for the perfect climate-neutral fuel. Every change in the fuel tank affects the engine. New combustion processes alter the requirements for lubricants. Different temperatures influence components, material properties and, ultimately, the entire design of the propulsion system.

The Marine Engineering Research Group is therefore pursuing its systemic approach entirely in line with the TUHH’s guiding principle, “Engineering to Face Climate Change”. Prof. Wirz’s team thus combines expertise from chemistry, mechanical engineering, naval architecture and measurement technology. Only by considering all these areas together can the complex interrelationships in the engine room of a modern ship be understood. Many of the insights gained can also be applied to land-based applications, such as stationary engine systems or commercial vehicles. The research thus not only contributes to reducing emissions in shipping but also supports the development of climate-friendly technologies in other industrial fields of application. “For us, ‘Engineering to Face Climate Change’ means not only analysing the challenges scientifically, but also actively contributing to the development of technical solutions through application-oriented research,” says Wirz. This is for a shipping industry that can continue to operate economically and in a climate-friendly manner in the future – and for which the research begins in the laboratory, amidst test tubes, metal rods and oil tests.

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