Large ships must run on green fuel

The maritime industry is currently working around the clock to find green alternatives to the fossil fuel used by ships—especially large container vessels. In the coming years, a collaborative project between Maersk Line, researchers at DTU, and several Chinese research institutions and companies will examine whether the gas dimethyl ether—abbreviated DME—can replace fossil fuel.

A.P. Moller - Maersk is committed to going carbon neutral by 2050 at the latest. COO of Maersk Line Søren Toft has no doubt that the solution to this must be found within the fuel used for ships.

“For nearby ships, solar power, batteries, fuel cells, etc. can be part of the solution, but for ships crossing the oceans, the answer is carbon-neutral fuel,” Søren Toft said to Jyllands-Posten in the autumn.

DME has special properties

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—e.g. in the form of bottled gas for the many kitchens without electricity.

“DME offers many advantages as a fuel. Above all, it’s simple to produce and has a 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. He elaborates:

“Unlike many of the other alternative fuels for ships such as natural gas and methanol, DME is also easy to ignite in the diesel engines typically used in large ships. This means that it’s easier to optimize the engine’s efficiency without sacrificing 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 a 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, the waste heat can be used 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.