Ammonia’s Achilles heel
Burning five times slower than fossil fuels and producing NOx emissions, researchers are invested in developing faster and cleaner combustion systems for green ammonia and exploring retrofit engine technology solutions.
Interest is growing in green ammonia as a fuel to decarbonise commercial shipping, as it may be more versatile than alternatives such as hydrogen. While ammonia can be synthetically created from the combination of nitrogen with hydrogen, green ammonia results when the process is emission free and powered by electricity from renewable energy sources, like wind, solar or geothermal.
The potential of other alternative fuels such as hydrogen have been thoroughly explored with limitations flagged in relation to hydrogen’s storage and transport capacity, because it requires compression and cannot easily be liquified, as it must be compressed with high pressure equipment that it is costly. However, ammonia can be easily liquefied at low pressures, allowing it to be stored much more easily, and safely, while having potential to be more economic and adaptable on an industrial scale.
Trials are exploring retrofitting diesel engines to burn ammonia. Compared to electric propulsion, these engines could move long-haul, large-scale ships. Batteries or fuel cells wouldn’t have the required energy density, but ammonia could achieve diesel-like efficiency and energy density. The caveat is that the nitrogen component of ammonia forms nitrogen oxide (NOx) greenhouse gases when burned.
Brainstorming NH3
MariNH3 is a new collaborative £5.5m EPSRC-funded initiative investigating the use of ammonia as a fuel for the long-haul shipping industry.
Nottingham University currently leads the research-driven consortium that will result in a road map of different vessels and propulsion types. The team will face the challenge of retrofitting existing engines of big ships, particularly around overcoming the problem of NOx emissions. As ammonia burns five times slower than fossil fuels, appropriate engines must be developed.
Industry partner MAHLE Powertrain will be helping with their Jet Ignition technology, a fast-burning combustion system used currently in Formula 1 engines, which could be transferred to marine to avoid or reduce NOx.
Professor Alasdair Cairns is director of Nottingham University’s Powertrain Research Centre and has more than 23 years’ experience in low-carbon engines and fuels. Fresh from his recent IMarEST branch lecture (link provided below) Professor Cairns tells Marine Professional that “the engine technologies range from dual fuel retrofit i.e. which can still revert to diesel-only operation when ammonia is not available, through to deep retrofit, modified engine components to enable the best trade-off between performance, efficiency and emissions.”
Ammonia research engine at University of Nottingham, UK (Credit: MAHLE)
The MariNH3 programme will explore longer term replacement engines, including the Dolphin N2 split cycle engine, which is cutting-edge engine technology that could achieve ultra-low NOx emissions, and optimum diesel-like engine efficiency making it the type of technology that could fuel the long-haul shipping industry while reducing its greenhouse gas emissions.
It is an exciting time to watch developments across the maritime sector. In January DNV has awarded approvement in principle (AIP) for an 81,000 DWT, ammonia-powered vessel developed by Sumitomo Corporation and Oshima Shipping in December 2021. And ClassNK has awarded MOL and Mitsui & Co. approvement in principle for its design of a large ammonia-powered bulk carrier.
Innovative retrofitted and advanced engines may find an answer to ammonia’s Achilles heel.
Watch the IMarEST TV recording of Ammonia Fuelled Engines for Marine Use - Greenwash or Green Future? presented by Professor Alasdair Cairns of the Powertrain Research Centre at the University of Nottingham in January this year.
Clarissa Wright is a freelance Science Journalist and Editor of NatureVolve