Wärtsilä 25 ammonia engine gets power upgrade
By on April 26, 2026
Equivalent to LNG-fueled engine
Click to learn more about the power upgrade to the Wärtsilä 25 Ammonia engine. Source: Wärtsilä.
Wärtsilä has announced an upgraded version of its four-stroke Wärtsilä 25 Ammonia engine, which is now released to the commercial market for deliveries in 2028. The upgrade raises power output to 315 kW per cylinder at 900 rpm and 345 kW per cylinder at 1000 rpm, matching the power level of Wärtsilä’s LNG‑fueled analog (the Wärtsilä 25DF engine). The increased power rating of 1.9-3.1 MW was demonstrated during type approval tests carried out in 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.
Stefan Nysjö, Vice President of Power Supply, Wärtsilä Marine, in his organisation’s official press release, 16 Apr 2026
Click to learn more. The current version of the Wärtsilä 25 Ammonia engine will feature aboard the Viking Energy retrofit. Source: Project Apollo.
Wärtsilä will provide one its current (non-upgraded) units to Skarv Shipping Solutions for deployment on a new timber transport vessel to be built at the Huanghai shipyard in China. The electric-ammonia hybrid vessel design was unveiled last year, and the first newbuild is expected to commence short-sea timber transport routes by mid-2027. As well as the engine itself, Skarv has also ordered Wärtsilä’s complete fuel gas supply system (AmmoniaPac), the Ammonia Release Mitigation System (WARMS), and a selective catalytic reduction (SCR) system designed for exhaust treatment from ammonia engines. Wärtsilä reports emissions from the WARMS system are nitrogen and water, with ammonia slip below 30 ppm (typically below 10 ppm, actual slip was 0 ppm in most testing cases). The engine and safety systems will also feature aboard the Viking Energy vessel retrofit.
In emissions testing results presented at the 31st CIMAC World Congress in 2025, Wärtsilä has demonstrated that an ammonia-fueled four-stroke engine (with ammonia fuel representing 95% of the energy share) achieves up to 90% percent greenhouse gas (GHG) emission reductions compared to equivalent diesel engines. Detailed N2O and NOX emission results were explored last year, and test results suggest that – with appropriate abatement systems, catalysts, and operating conditions – ammonia-fueled engines are well compliant with IMO limits, and potentially less-polluting than diesel engine analogs.