Wärtsilä Announces Higher Power Rating for Ammonia Engine

Wärtsilä has announced 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‑fueled 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‑fueled 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‑fueled 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-fueled 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.

Ammonia is increasingly recognized 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 increased power version of the Wärtsilä 25 Ammonia engine is now released to the commercial market for deliveries in 2028.