The world’s first full-scale commercial ammonia-fuel engine has been completed by Japan Engine Corporation (J-ENG), marking a milestone in efforts to decarbonise global shipping.
A large (50cm) bore, seven-cylinder engine intended for medium gas carriers, a mid-sized class of commercial gas-transport vessels, it is equipped with high-pressure selective catalytic reduction (SCR).
The engine passed its official test programme between 27 and 30 August at J-ENG’s factory in Japan. Testing was conducted under the supervision of groups involved in marine engineering and shipbuilding, specifically Nippon Yusen Kaisha (NYK Line), Nihon Shipyard (NSY), and Japan Marine United Corporation (JMU), in addition to ClassNK, a standards group in the area of marine safety and environmental compliance.
The trials included verification in both ammonia and heavy fuel oil dual-fuel operation modes, followed by post-operation inspections. ClassNK has certified the engine’s safety and environmental performance.
It is scheduled to ship in October 2025 for installation on an ammonia-fuelled medium gas carrier under construction at JMU’s Ariake Shipyard, with the vessel expected to enter service in 2026.
One matter that has occupied the developers of ammonia engines to date is air quality and the need to minimise the emissions of nitrogen oxides, for example.
At full load with 95% ammonia co-firing, trial runs on the J-ENG engine seemingly measured nitrous oxide (N2O) emissions at approximately 3 ppm — a very low level compared with typical fossil-fuel engines. Overall greenhouse gas emissions were reduced by more than 90% compared with conventional heavy fuel oil. Nitrogen oxide (NOx) emissions were roughly half those of traditional heavy oil engines, while unburned ammonia was effectively eliminated using the post-combustion SCR system. The engine’s thermal efficiency in ammonia mode was confirmed as being equivalent to, or exceeding, that in heavy oil operation.
Seemingly complementary research on the development of ammonia-compatible SCR systems is underway at the University of Sheffield (and explored here).
Development of this engine drew on more than 1,000 hours of single-cylinder testing carried out between 2023 and 2024 at Mitsubishi Heavy Industries’ R&D Centre in Nagasaki, said J-ENG. The full-scale unit has since undergone around 700 hours of testing, focusing on performance optimisation, leak prevention, and safety systems for handling toxic ammonia.
Alongside the 50 cm bore model, J-ENG is also developing a 60 cm bore ammonia-fuelled engine to serve a broader range of ship types expected to enter the market.
The company is planning a new factory, supported by the Japanese governemnt, which is expected to open in 2028, to increase production of ammonia-fuel engines alongside heavy oil engines to accelerate deployment of zero-emission ships.
