Researchers investigate new green fuel for ships

Tuesday 08 Oct 19

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Anders Ivarsson
Associate Professor
DTU Mechanical Engineering
+45 45 25 42 30

Gas produced from bio-waste and wind may make future shipping traffic more climate-friendly.

The maritime industry is currently working hard to find green alternatives to the fossil fuel used by ships, especially large container vessels. This requires a new and efficient type of fuel that can be safely distributed and stored during shipping.

In the coming years, a collaborative project between China, Maersk , and researchers at DTU will investigate whether the gas dimethyl ether, or DME, can provide the solution to this challenge. DME is best known in our part of the world as the propellant used in hairspray and other products. DME is produced and used more widely in China, for example in the form of bottled gas for the many Chinese kitchens without electricity.

“DME has many advantages as a fuel. Above all, it’s simple to produce and has high energy efficiency. It’s not a greenhouse gas, is not toxic, and it can be stored safely with high energy density at low pressure, just like camping gas,” says Associate Professor Anders Ivarsson from DTU’s Department of Mechanical Engineering, who is heading the project.

“Unlike many of the other alternative fuels for ships such as natural gas and methanol, DME is also easy to ignite in diesel engines, which are typically used in large ships. This means that it’s easier to optimise the engine’s efficiency without sacrificing its reliability.  In addition, DME doesn’t produce soot, and the nitrogen oxide emissions are very low when DME’s unique combustion properties are used optimally.”

Green production

In the coming years, the project will investigate whether producing green DME can be made competitive, and how marine engines can be equipped to use DME as fuel.

Currently DME is mainly produced in China using coal and natural gas, so the project will also examine whether it is possible to produce the gas from biomass and hydrogen extracted from electricity generated by wind turbines. Both are abundant in China, where agricultural waste products can be used and hydrogen can be produced from surplus electricity when the needs of the grid have been met.

The team also wants to study DME’s combustion properties under high pressure in more detail. These properties will be examined theoretically and experimentally with the same types of experiments that have increased our understanding of diesel spray combustion over the past thirty years. The experiments will be carried out in DTU Mechanical Engineering’s new high-pressure combustion laboratory in order to gain insight into how DME can best be injected under engine-like conditions.

Utilization of waste heat

“A number of these experiments will focus on how the waste heat from an engine fuelled by DME can be used. Because the gas doesn’t contain sulphur or produce soot during combustion, it will possible to use the waste heat derived from it directly in heat exchangers, which can supply power to the ship via a turbine. This will make it possible to replace the current engines which are used, for example, to cool containers in the cargo, further reducing carbon emissions,” says Anders Ivarsson.

DTU already has experience with the use of DME in diesel engines. Diesel engines are based on the principle behind the engine invented by Rudolf Diesel. In diesel engines the fuel self-ignites when it is injected into compressed hot air under high pressure. By contrast, in the spark-ignition engines used in petrol-fuelled cars, a spark is used to ignite a prepared mixture of air and fuel.

The diesel engine will continue to be the best choice for heavy traffic because it has lower fuel consumption and is more durable than petrol engines. Using DME as a fuel will solve the diesel engine’s biggest problem: the emission of soot and nitrogen oxide. In modern diesel vehicles, soot and nitrogen oxide are removed efficiently, but expensively, with a filter and catalytic converter. On ships, this type of exhaust-gas cleaning is a particular challenge because it takes up a lot of space that could otherwise be used for cargo.

The project will conclude with a business case to show whether DME will be a good fuel choice, for example for Maersk, when the company buys new ships to realise its ambition to become carbon-neutral by 2050.

The project is partly funded by the Danish Ministry of Foreign Affairs and is administrated by the Danida Fellowship Center. The participation of a number of major Chinese partners was made possible by the China-Europe Productivity Center. In addition to the Chinese partners, Maersk , Alfa Laval, Green Hydrogen, and Danfoss are taking part in the project, which is being led by DTU Mechanical Engineering.