Wärtsilä's Ammonia Marine Engine Cuts Emissions by 90%

by Ship & Bunker News Team
Tuesday May 27, 2025

Finnish marine propulsion firm Wärtsilä has announced that its four-stroke ammonia engine now achieves up to a 90% reduction in GHG emissions compared to diesel engines.

This breakthrough follows extensive testing of the Wärtsilä 25 ammonia engine, the firm said in an emailed statement on Tuesday.

Using a low-pressure Otto cycle - a design known for safety and efficiency - the engine runs on a 95% ammonia energy share to deliver 90% GHG reduction.

Ammonia engines require a certain amount of conventional fuel or pilot fuel, such as diesel, to initiate combustion. This is because ammonia has a higher ignition temperature and lower flammability compared to traditional marine fuels, making it difficult to ignite on its own.

This ratio could vary by about 5-10% depending on the engine manufacturer's specifications.

Wärtsilä aims to begin the first deliveries of its ammonia engines from 2026.

"With decarbonisation front and centre of our company strategy, we have continued to enhance the capabilities of our ammonia engine solution - adding even more safety features and further improving its performance," Stefan Nysjö, vice president of power supply at Wärtsilä Marine, said.

"This is in line with our commitment to 'continuous improvement', whereby we continue to develop, test and enhance new and current technologies and solutions which will support the industry with making meaningful reductions in greenhouse gas emissions."

Ship & Bunker News Team
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