Japan Engine completes hydrogen-fueled marine engine; moves to ship installation

# What happened Japan Engine Corporation has completed a hydrogen-fueled marine engine called the 6UEC35LSGH. In land-based factory testing the engine reached a hydrogen co-firing rate of at least 95% and achieved more than a 95% reduction in greenhouse gas emissions compared with a conventional heavy-fuel-oil engine, according to project partners.

# Who developed it The engine was developed under Japan's NEDO Green Innovation Fund. The development partners are Japan Engine, Kawasaki Heavy Industries and Yanmar Power Solutions. ClassNK attended approval testing and the tests were completed successfully.

# How the engine works The 6UEC35LSGH uses a high-pressure direct injection system to inject hydrogen directly into the combustion cylinder. The system is engineered to maintain stable hydrogen combustion at the conditions needed for large commercial vessel engines.

Safety measures were built into the design to address hydrogen-specific risks. Those measures include a structure meant to prevent hydrogen leakage and double-walled piping for the hydrogen fuel supply lines.

# Next steps: ship installation, sea trials, demonstration

Kawasaki Heavy Industries will provide the Marine Hydrogen Fuel System (MHFS) for the vessel. The MHFS covers hydrogen fuel tanks and the equipment to supply hydrogen to the engine. Kawasaki will also develop and manufacture liquefied-hydrogen bunkering equipment for supplying the vessel.

After installation the ship will undergo sea trials followed by onboard demonstration operations. Onboard testing is scheduled to begin in April 2028. The programme will measure durability and performance under real operating conditions. ClassNK will continue to conduct safety assessments that cover the engine plus the vessel's design, construction and operation.

# Context in marine fuels development Japan Engine previously completed an ammonia-fueled low-speed two-stroke marine engine in August 2025. The hydrogen engine represents another step toward testing next-generation marine fuels aboard commercial vessels rather than limiting them to lab or land-based development.

# What this means for ship operators and suppliers

• Operators: The announcement signals a near-term pathway to operate large commercial vessels using primarily hydrogen, with demonstration runs planned within two years of installation.

# Bottom line A land-tested hydrogen engine has met high hydrogen-firing ratios and large GHG reductions in factory testing, with a clear plan to install the unit on a working multipurpose vessel in early 2027 and begin onboard demonstrations in 2028. The effort brings hydrogen propulsion closer to real-world commercial evaluation, while requiring coordinated development of shipboard fuel systems and bunkering capability.