Wartsila’s 4‑stroke engine solution for ammonia fuel now offers a higher power rating, with an upgrade to the Wärtsilä 25 Ammonia engine, designed as part of the company’s continuing development of ammonia‑fuelled engines.
The upgrade 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 is intended to reduce installation complexity and simplify maintenance. This supports more flexible and efficient vessel designs for ammonia‑fuelled applications.
The power increase 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 seen as a suitable choice for a wide range of applications, both as a main engine or as an auxiliary engine. 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 has been demonstrated during type approval tests carried out in autumn 2025 under the supervision of classification society representatives.
Stefan Nysjö, VP Power Supply, Wärtsilä Marine, said: “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.”
Ammonia is increasingly recognised as an important alternative fuel as the marine industry works towards meeting international emissions reduction targets. With the IMO setting goals for reducing GHG emissions from shipping, the shift away from conventional fossil fuels is expected to accelerate in the coming years.
The Wärtsilä 25 engine platform is said to be 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 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.
Image: Wärtsilä’s 4‑stroke ammonia-fuelled engine solution now offers a higher power rating (credit: Wärtsilä Corporation)
