The International Energy Agency (IEA) expects ammonia to become one of the key green fuels for ensuring carbon-neutral shipping in the future. According to their predictions, it will account for about half the maritime fuel consumption by 2070. Other sources in the maritime industry expect ammonia to account for between 30 and 40 per cent of the total consumption already in 2050.
However, it will take much work to get there, as ammonia is not ideal as a fuel, and the current marine engines cannot immediately run on ammonia.
Since 2020, MAN Energy Solutions has therefore been working to develop an engine that can be ammonia fuelled and thus meet the climate requirements for shipping.
“We expect that the first commercial engine will be delivered in the beginning of 2025, and that we will then be ready with the design of several engine sizes for our customers, who have shown great interest and have long been asking about ammonia-fuelled engines. We are currently testing our full-scale two-stroke trial engine in Copenhagen. The next and final step will then be to test the ammonia-fuelled engine at one of our licensees and subsequently on a sailing ship,” says Principal Project Manager Johan Kaltoft, MAN Energy Solutions.
Safety first
Ammonia is toxic, and a large part of MAN Energy Solutions’ work has therefore revolved around safety in connection with bringing the ammonia engine to run in Copenhagen and to bring it into the engine room on a marine vessel.
“It’s crucial that safety is high. Ammonia emissions mustn’t be possible, so this has had top priority in our work. The authorities responsible for approvals and legislation on ammonia-fuelled engines will undoubtedly also focus on ensuring that safety is fundamentally in order, so that it doesn’t pose any hazard to people or the environment.”
Close collaboration with researchers
MAN Energy Solutions’ work to convert a large diesel engine intended for heavy fuel oil into an engine that uses ammonia has comprised a number of collaboration projects with researchers at DTU, who were among the first in the world to examine the properties of ammonia as fuel for ships.
“Our work began 18 years ago. At that time, people shook their heads in disbelief and didn’t understand why we wanted to use toxic ammonia as fuel. But ammonia has the great advantage that it doesn’t contain carbon and consequently doesn’t contribute to CO2 emissions. It was therefore an interesting candidate as a fuel,” says Associate Professor Anders Ivarsson, DTU.
In addition to being toxic, ammonia also poses a challenge in terms of securing quick ignition and combustion. The researchers have focused on examining this on two small internal combustion engines located in DTU’s laboratories.
“At the outset, we worked with adding a so-called ignition enhancer, for example hydrogen, which could be used to ignite the ammonia. In our latest tests, however, we’ve shown that it’s possible to ignite ammonia without adding other fuels,” says Anders Ivarsson.
Another part of the researchers’ work concerns the details of the ammonia combustion process in the engine. A so-called combustion bomb with glass windows makes it possible to study the individual elements in the process, for example the flame or the atomization of spray from the nozzle that injects the fuel. At the same time, the researchers can adjust the individual parameters, for example by adding heat or oxygen and see how the individual parts react and thus achieve the most optimal combustion.
"You can’t just insert a sensor in an ammonia-fuelled engine and gain knowledge about details of this type. Therefore, we perform a number of different, well-controlled tests in our laboratories, which together contribute significant knowledge about the individual steps in the combustion process, which the designers use to understand and optimize the final ammonia-fuelled ship engine,” explains Anders Ivarsson.
Emissions are important
The researchers have also contributed to evaluate the emissions from an ammonia-fuelled engine. Combustion of ammonia causes the formation of nitrogen oxides (NOx) and nitrous oxide (N2O). These emissions are harmful to the environment and must be as low as possible, so the combustion of ammonia does not simply replace one problem with another. Especially nitrous oxide emissions are problematic, as it is a much more powerful greenhouse gas than CO2.
“This means that an ammonia-fuelled engine doesn’t need to have a large emission of nitrous oxide before the benefit in the form of lower CO2 emissions is eliminated,” says DTU Professor Peter Glarborg.
“We have one of the world’s leading laboratories for studying chemical reactions at high temperature. Here, under realistic conditions, that is under the same high pressure as in an engine with about 100 atmospheres of pressure, we can examine the oxidation of ammonia under controlled conditions. This has given us knowledge about the chemistry of the process and insight into how emissions from the combustion of ammonia are limited optimally,” says Peter Glarborg.
A complete model and new measuring methods
The results from all parts of the researchers’ work provide input for the Computational Fluid Dynamics (CFD) model which MAN Energy Solutions use to predict engine performance complementing the large-scale tests.
“The model simulates in detail the processes that occur in the ammonia-fuelled engine. This is important in the development work so that you can quickly and easily test on the model to achieve, for example, the most optimal combustion, rather than having to calibrate and convert a large test engine and then wait for the results,” says Peter Glarborg.
Although the researchers at DTU are among the best in the world when it comes to knowledge about ammonia as a fuel, they have ventured into uncharted territory in their collaboration projects with MAN Energy Solutions and have had to develop new methods.
“Measuring emissions from combustion of ammonia sounds easy. But it’s an exhaust gas with a high moisture content that must be analysed for the content of unburnt ammonia as well as small quantities of nitrous oxide and other undesirable components. This means that we haven’t been able to use our normal measurement procedures and equipment. It has been necessary to develop new methods for gas analysis, and we’ve collaborated with some of the world’s leading researchers in measuring nanoparticles from the Greek Aristotle University of Thessaloniki. They’ve sent all their finest measuring equipment and two researchers to our laboratory for three weeks to perform measurements on our ammonia-fuelled engine,” says Anders Ivarsson.
Great confidence in coming ammonia-fuelled engine
However, the researchers show great optimism.
“The greatest challenge is no longer of a technical nature, getting an ammonia-fuelled engine to work. The biggest hurdle right now is to produce sufficient quantities of green ammonia to be used in shipping so that the industry can reduce its climate footprint,” says Peter Glarborg.
Anders Ivarsson completely agrees.
“You may quote me for saying that great progress is currently being made in the development of the use of ammonia in a marine engine. It’s a very promising fuel for large ships which I believe will play an important role in the future.”