Technology group Wärtsilä announces that its 4‑stroke engine solution for ammonia fuel now offers a higher power rating. As part of the company’s ongoing development of ammonia‑fuelled engine solutions, the upgrade to the Wärtsilä 25 Ammonia engine raises output to 315 kW per cylinder at 900 rpm and 345 kW per cylinder at 1000 rpm, matching the power level of the LNG‑fuelled Wärtsilä 25DF engine. A key benefit of the upgrade is that fewer cylinders are required for a given power demand, which will reduce installation complexity and simplify maintenance. This supports more flexible and efficient vessel designs for ammonia‑fuelled applications.
The power increase also supports the conversion of the engine between LNG and ammonia fuel operation. With this new power range of 1.9-3.1 MW, the Wärtsilä 25 Ammonia engine is an ideal choice for a wide range of applications, both as a main engine or as an auxiliary engine. What’s more, by aligning with the power level of the LNG-fuelled Wärtsilä 25DF, retrofitability is improved resulting in greater flexibility in fuel choice for shipowners. The increased power rating was demonstrated during type approval tests carried out in autumn 2025 under the supervision of classification society representatives.
“With decarbonisation front and centre of our strategy, we continue to enhance the capabilities of our ammonia engine solution. This power increase builds on our extensive testing and development work and helps make ammonia‑fuelled ship operations more practical and affordable, while maintaining high standards of safety and reliability,” says Stefan Nysjö, Vice President of Power Supply, Wärtsilä Marine.
Ammonia is increasingly recognised as an important alternative fuel as the marine industry works towards meeting international emissions reduction targets. With the International Maritime Organization setting clear goals for reducing greenhouse gas emissions from shipping, the shift away from conventional fossil fuels is expected to accelerate in the coming years.
The Wärtsilä 25 engine platform is a next-generation, medium-speed marine engine designed for safe and reliable power generation, low emissions, efficient operation and easy integration. The Wärtsilä 25 Ammonia features a modular design and delivers proven reliability for a wide range of vessels and propulsion arrangements.
The increased power version of the Wärtsilä 25 Ammonia engine is now released to the commercial market for deliveries in 2028.
Media contact for more information on this release:
Isabella Alder
Positioning and Strategic Communications Manager
Wärtsilä Marine
Tel: +44 (0) 7792 681 757
marine.media@wartsila.com
Image caption: Wärtsilä’s 4‑stroke engine solution for ammonia fuel now offers a higher power rating © Wärtsilä Corporation
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Wärtsilä Marine in brief
Wärtsilä Marine is a global pioneer in power, propulsion and lifecycle solutions for the marine market. We develop industry-leading technologies, advancing maritime's transition to new fuels. We support building an end-to-end digital ecosystem where all vessels and ports are connected. Ultimately, Wärtsilä Marine is driving the shipping industry forward on its journey towards a decarbonised and sustainable future through our broad portfolio of engines, propulsion systems, hybrid technology, exhaust treatment, shaft line solutions and digital technologies, as well as integrated powertrain systems. Our offering, which is underpinned by our performance-based agreements, upgrades, lifecycle solutions, decarbonisation services, as well as an unrivalled global network of maritime expertise, delivers the efficiency, reliability, safety, and environmental performance needed to support a safe and sustainable future for our customers, our communities and our planet.
www.wartsila.com/marine
Wärtsilä in brief
Wärtsilä is a global leader in innovative technologies and lifecycle solutions for the marine and energy industries. We emphasise innovation in sustainable technology and services to help our customers continuously improve environmental and economic performance. Our dedicated and passionate team of 17,900 professionals in 199 locations in 78 countries shape the decarbonisation transformation of our industries across the globe. In 2025, Wärtsilä’s net sales totalled EUR 6.9 billion. Wärtsilä is listed on Nasdaq Helsinki.
www.wartsila.com
