The Japanese island of Naoshima is a renowned mecca of creativity for its art installations like Yayoi Kusama’s enormous plastic pumpkins. Just across an inlet on the Seto Inland Sea, however, giant tanks of ammonia are powering a new source of innovation that the crowds of art lovers don’t see. At Mitsui E&S Group’s Tamano Factory, a revolutionary dual-fuel engine is being put through its paces using ammonia fuel for carbon-neutral shipping. 

After intensive R&D began at Everllence’s Research Centre Copenhagen (RCC) in 2019, engineers successfully ran the two-stroke ammonia research engine on one cylinder in July 2023, and on all four cylinders in November 2024. This milestone paved the way for the commercial dual-fuel ammonia engine that is now being built at Japan’s Mitsui E&S, a trusted Everllence licensee that developed the world’s first LNG-fuelled engine in 1994. Testing of the engine is being carried out in collaboration with experts from Everllence.

“Here at Mitsui E&S, we’re not only developing the engine, but also an ammonia supply system,” says Takahiro Murakami, manager in the Ammonia Project Group at the Tamano Factory. “This engine has been run on methanol and LPG. Now, with ammonia, it will have basically no CO₂ emissions. While ammonia and hydrogen can both help reduce emissions, ammonia is easier to handle.”

The challenge of achieving carbon neutrality in shipping

The international shipping industry, responsible for moving roughly 90 percent of global trade, faces one of its greatest challenges: achieving carbon neutrality. Despite being among the most efficient modes of transport per ton-kilometer, shipping still emits about three percent of global greenhouse gases. With international regulations tightening — most notably through the International Maritime Organization’s (IMO) target to reach net-zero emissions by 2050 — the industry is under mounting pressure to decarbonize without disrupting global trade.

Long used as a fertilizer feedstock, ammonia is now a leading candidate for green marine fuel. When produced from renewable energy — using green hydrogen synthesized via electrolysis and nitrogen extracted from the air — ammonia contains no carbon and emits no CO₂ when burned.

However, ammonia is toxic, requiring strict safety protocols to prevent leaks, and its combustion can produce nitrogen oxides (NO_x), which must be mitigated through advanced catalytic converters. Concerns about these aspects need to be addressed through proper protocols and technology.

Even before entering Mitsui E&S’s testing area, visitors are introduced to ammonia during a safety briefing. A dab of ammonia water is applied to a tissue and passed around for sniffing. To call the chemical pungent would be a gross understatement. Even in its diluted form, the acrid smell is overpowering. 

"People often get anxious when they are faced with something new,” says Michael Foteinos, engine performance engineer in Everllence’s dual-fuel department in Copenhagen. “I’ve read about the reaction of British admirals when the first oil-fuelled engines were introduced. They were concerned about how explosive it was. And in the early 2000s, everyone was paying extra attention to the safety of early LNG engines. So I think it’s inherent in human nature to be anxious about anything new, and the same is true with ammonia.”

Limited refuelling options

Most ammonia today is produced from natural gas. Scaling up production of truly green ammonia will also demand vast renewable power capacity and new global supply chains. Traditional fuels such as heavy fuel oil and marine diesel are cheap and energy-dense but extremely carbon-intensive. Replacing them is far from straightforward. Ships must travel long distances across oceans where refuelling options are limited, and alternative energy sources need to match the reliability and power density of fossil fuels while being safe and cost-effective.

Battery power, for instance, works well for short-distance ferries but remains impractical for large ocean-going vessels due to weight and energy limitations. Similarly, hydrogen offers a promising zero-carbon pathway but requires high-pressure storage or cryogenic conditions, which present significant engineering challenges for ships. Due to the low energy density of hydrogen, the tanks required for such transoceanic routes would have to be so large that they would no longer fit on the ship.

Ammonia represents one of the viable pathways toward carbon-neutral shipping along with other zero or near-zero emission fuels. If supported by coordinated investments, regulatory frameworks, and innovation in ship design and port infrastructure, this zero-carbon fuel could help steer the global maritime sector toward a sustainable future.

More than 200 sensors

Steps away from the seaside tanks of ammonia, the No. 7-D engine test bed hums with energy that shakes the cavernous hangar. The fuel is transferred from the tanks into the supply system that runs at a pressure of around 80 bar through the engine in a loop. The injectors pressurize the fuel to around 650 bar. Ammonia has a vapor pressure of about 9 bar so it will always remain liquid during the pressure steps. The pipes containing ammonia are double-walled to prevent leaks, and there is a multitude of sensors — inside and around the engine — to pick up any ammonia that has escaped.

Some three floors tall, the 60-bore Everllence B&W 7S60ME-LGIA (Liquid Gas Injection Ammonia) Mk 10.5 engine is also attached to a selective catalytic reduction (SCR) reactor to reduce NO_x emissions. Harmful NO_x is converted into harmless nitrogen and water by adding urea or ammonia to the exhaust gas.

The more than 200 sensors create a detailed heat map of the combustion chamber for monitoring at an Everllence test center in a shipping container. Here, in the relative quiet surrounding a bank of computer screens, staff pore over displays of incoming and past data while communicating with the Mitsui E&S engine control room overlooking the hangar.

“We are essentially building a full-scale engine lab remotely,” says Tobias Stübbe, a research engineer in Everllence’s dual fuel-department in Copenhagen. “It’s not just about performance and emissions. We also get data on mechanical stress, control systems and hydraulic behavior.”

After more than a year of tests and adjustments, the Everllence team is satisfied with their results.

“We are happy to say that we have a stable and reliable engine,” says Foteinos. “Our tests show ammonia combustion results in very low NO_x emissions, while keeping ammonia emissions well within acceptable limits. Engine operation remains stable even at very low loads, and the transition between diesel and ammonia is seamless."

The emissions of nitrous oxide (N₂O), a very potent greenhouse gas, have also been closely monitored. Numerous tests, measurements, and observations have revealed that with the right tuning, the engine runs in a way that prevents conditions where N₂O could form.  

The ammonia two-stroke engine is no longer new technology for Everllence, as it has been thoroughly tested by their experts. But it's new for shipowners and crews who will need specific trainings for the engine, the auxiliary systems and safety procedures. "We as a company have been cautious about ammonia, now we respect it and know how to handle it — competence in the handling of ammonia and the safety features around it is key", says Daniel Struckmeier, Managing Director of Everllence Japan Ltd. "Ammonia as a marine fuel is a viable solution and very much part of the predicted future fuels mix by 2050."

About the author

Timothy Hornyak is a Tokyo-based author and journalist covering Japanese technology, business, and culture.