Finnish technology group Wärtsilä has increased the power rating of its Wärtsilä 25 Ammonia engine, bringing ammonia‑fuelled operation up to the same output as the company’s LNG‑fuelled Wärtsilä 25DF unit. The upgraded four‑stroke engine now delivers 315 kW per cylinder at 900 rpm and 345 kW per cylinder at 1000 rpm, enabling fewer cylinders for the same total power and reducing installation complexity and maintenance demands.
The higher rating expands the engine’s power range to 1.9–3.1 MW, making it suitable as either a main propulsion or auxiliary engine across a wider set of vessel types and applications. By aligning ammonia engine performance with the LNG‑fuelled platform, Wärtsilä improves the technical and economic case for switching between the two fuels, as well as for future retrofits.
The upgrade was validated during type approval tests in autumn 2025, carried out under classification society supervision. The elevated output version of the Wärtsilä 25 Ammonia is now available for commercial orders, with deliveries scheduled from 2028.
Ammonia is increasingly viewed as a key alternative fuel as the maritime sector works to meet the International Maritime Organization’s greenhouse gas reduction targets. With the Wärtsilä 25 platform designed as a modular, medium‑speed engine, the enhanced ammonia version supports both cleaner power generation and more flexible vessel design as shipowners weigh long‑term fuel strategies.
