Japan Engine Corporation (J-ENG) and Kawasaki Heavy Industries have achieved hydrogen co-firing operation across all cylinders of a full-scale marine engine intended for installation on a commercial vessel, according to an announcement from the consortium.

The 6UEC35LSGH engine, described by J-ENG as the world's first full-scale hydrogen-fuelled main engine for a large commercial vessel, has reached a hydrogen co-firing ratio of over 95% at 100% load during factory testing. The engine is a large, low-speed, two-stroke design developed for oceangoing applications.

The development forms part of the New Energy and Industrial Technology Development Organization's (NEDO) Green Innovation Fund Project, which focuses on marine hydrogen engines and fuel systems. The consortium includes Mitsui O.S.K. Lines (MOL), MOL Drybulk, Onomichi Dockyard, and classification society ClassNK.

J-ENG stated that verification testing will continue to optimise performance under hydrogen co-firing conditions. The engine is scheduled for shipment in January 2027 and will be installed as the main engine of a 17,500-deadweight-tonne hydrogen-fuelled multipurpose vessel being built by Onomichi Dockyard.

The project combines the two-stroke engine with liquefied hydrogen fuel, enabling what the consortium describes as long-distance, long-duration, and high-output operations. This contrasts with existing hydrogen vessel demonstrations, which have primarily focused on short-distance applications such as sightseeing boats or tugboats using compressed hydrogen for coastal or port operations.

Kawasaki is developing and manufacturing the Marine Hydrogen Fuel System (MHFS), which will supply hydrogen to the engine aboard the vessel. MOL and Onomichi Dockyard have concluded construction contracts, and detailed design of the vessel is underway.

The vessel is scheduled to begin three years of demonstration operation in fiscal year 2028 under the operation of MOL and MOL Drybulk. ClassNK will conduct safety evaluations throughout the development, construction, and operational phases.

J-ENG noted that it has accumulated expertise through studies on hydrogen-related materials and combustion, as well as durability testing of hydrogen fuel injection systems. The company began testing of hydrogen fuel injection devices for large low-speed two-stroke engines in May 2023, and achieved land-based operation of a marine hydrogen engine in October 2025.

The consortium received approval in principle for the hydrogen-fuelled vessel design from ClassNK in October 2023. In February this year, Kawasaki was selected for a separate NEDO Green Innovation Fund project focused on automation technology for liquefied hydrogen bunkering.