Wärtsilä four-stroke ammonia engine cuts GHG emissions up to 90%

The Wärtsilä 25, a four-stroke engine-based solution for ammonia fuel first introduced to the commercial marine sector in November 2023, has undergone extensive testing to optimize its performance parameters, said Wärtsilä. The latest results show a 95% ammonia energy share now achieves up to a 90% reduction in greenhouse gas (GHG) emissions compared to equivalent diesel engines, the company reported, which represents a further 18% improvement in emissions performance.

In the latest testing of the Wärtsilä 25 ammonia, a 95% ammonia energy share was shown to achieve up to a 90% reduction in GHG emissions compared to equivalent diesel engines. (Photo: Wärtsilä)

The latest results were assessed against the FuelEU Maritime reference and measured on both a Well-to-Wake and Tank-to-Wake basis.

The ammonia engine, which is available as part of the Wärtsilä 25 engine platform, was developed based on safety and operational experience gained from low-pressure dual-fuel (DF) engines running on LNG. The company said the recent tests have shown ammonia to be a suitable fuel for the low-pressure Otto cycle concept, which is the design that it has utilized for its ammonia engine solution.

The decision to opt for a low-pressure Otto cycle concept was based on several factors, including safety, efficiency and overall potential for GHG reduction, among several other parameters. Comprehensive tests conducted on different engine sizes have shown that the efficiency of the low-pressure Otto cycle concept is consistent with, and equal to, that of dual-fuel LNG engines, Wärtsilä stated. Ammonia is also highly knock resistant, with robust combustion capabilities across a range of engine settings.

The enhancements made to the ammonia engine’s performance benefit the entire ammonia solution, which is comprised of an AmmoniaPac fuel gas supply system, Wärtsilä Ammonia Release Mitigation System (WARMS) and Wärtsilä NOx Reducer (NOR) for exhaust aftertreatment. Safety, efficiency and reliability are maximized by a sophisticated automation system and maintenance agreement designed to ensure safe and efficient onboard operations, the company added.

Alongside future engine orders, the enhanced performance will be integrated into engines already contracted as first deliveries, which are due to take place from 2026 onwards.

Wärtsilä’s ammonia-fueled four-stroke engine First commercially available four-stroke engine-based solution for ammonia fuel announced