Wärtsilä 25 Ammonia engine power increased

Wärtsilä has announced that its four‑stroke engine solution for ammonia fuel, the Wärtsilä 25 Ammonia, now offers a higher power rating. The solution has been released to the commercial market for deliveries in 2028

The engine upgrade raises the power range of the the Wärtsilä 25 Ammonia to 1.9 to 3.1 MW. (Source: Wärtsilä)

The engine upgrade raises output to 315 kW (422.4 hp) per cylinder at 900 rpm and 345 kW (462.7 hp) per cylinder at 1,000 rpm, matching the power level of the LNG‑fueled 25DF engine. With its new power range of 1.9 to 3.1 MW, the 25 Ammonia is suited for applications as a main engine or as an auxiliary engine.

According to the company, with the increased power, fewer cylinders are required for a given power demand, which can reduce installation complexity and simplify maintenance. The increased power also supports the conversion of the engine between LNG and ammonia fuel operation and improves retrofitability.

The higher power rating was demonstrated during type approval tests carried out in Autumn 2025 under the supervision of classification society representatives.

“This power increase builds on our extensive testing and development work and helps make ammonia‑fueled ship operations more practical and affordable, while maintaining high standards of safety and reliability,” said Stefan Nysjö, vice president of Power Supply, Wärtsilä Marine.