Fuel suppliers working on framework for green ammonia production
The fuel can be categorized as “brown” (produced from fossil sources), “blue” (produced from fossil sources with carbon capture) or “green” (produced from renewably sourced hydrogen in a process called electrolysis). “While the production of blue ammonia results in 85 per cent less CO2 emissions than brown variants, only green ammonia is a zero-carbon fuel,” he adds.
The crux is: green ammonia is currently not produced anywhere. This is expected to change over the coming decade. “Several fuel suppliers are already doing a lot of work on the necessary framework for producing green ammonia, including certification, technology and costs,” says Brinks.
Engine technology: First ammonia-fuelled engine by 2024
While the supply of green ammonia will take time, the development of engine technology is progressing fast. In the AEngine joint development project (JDP), MAN Energy Solutions, Eltronic FuelTech, the Technical University of Denmark and DNV are working together on developing the first dual-fuel ammonia- powered combustion engines. With combustion testing scheduled for this spring, MAN’s two-stroke model is expected to go to market in 2024.
Combustion: Ammonia burns more slowly than other fuels
Unlike diesel oil, ammonia has a very slow flame propagation, which means it burns much more slowly. Its autoignition temperature is also a lot higher, at around 630°C – diesel oil burns at 210°C. This means that sustaining combustion once it gets started is also more difficult with ammonia than with other fuels.
“And, of course, you also need to ensure that the engine allows for the usual performance peaks that come with acceleration, etc. We are planning for a final fuel mix that would contain around 95 per cent ammonia and 5 per cent of a pilot fuel such as marine gas oil. In the future this could even be biofuel,” says Kirkeby.
Harmful emissions could be mitigated by combustion process
Mitigating harmful emissions is another significant challenge, even with green ammonia. While carbon- free, ammonia contains a lot of nitrogen, and burning it is likely to result in both nitrogen oxide (NOX) and nitrous oxide emissions. Kirkeby explains that NOX emissions weren’t so much of an issue for the engine manufacturer. “They are well-regulated and the abatement technology for NOX – selective catalytic reaction – is already used on many ships and should also be suitable for ammonia. Nitrous oxide emissions are the greater challenge. N2O, or laughing gas, is a very aggressive greenhouse gas that is 283 times stronger than CO2. Our approach is to use the combustion process itself to mitigate these emissions.”
In the AEngine JDP, MAN Energy Solutions,
Eltronic FuelTech, the Technical University of Denmark and DNV are working on the development of the MAN ME-LGIa ammonia-burning engine.
“As an engine designer we are agnostic when it comes to the different fuel types,” says Peter H. Kirkeby, Principal Specialist, Dual-Fuel Engines at MAN Energy Solutions. “Ammonia has generated a lot of interest, especially from the deep-sea ship segments, and it has a lot of potential – but developing an engine that is powered by ammonia has been a challenge. One of the biggest hurdles is how to burn ammonia efficiently to extract the maximum amount of power while making sure the engine is still a compact design.”
We have to make it a very simple system that can also handle ammonia – meaning that it is modular enough to allow for easy troubleshooting and for crews to have straightforward maintenance procedures even though the fuel is a toxic substance.
Peter H. Kirkeby is Principal Specialist, Dual-Fuel Engines at MAN Energy Solutions. He says, “Through combustion tuning, we can either stay clear of that window or we can go into
The Report • June 2022 • Issue 100 | 59
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