Wärtsilä's 4-Stroke Ammonia Engine Put to the Test

Wärtsilä’s 4-stroke engine-based solution for ammonia fuel now delivers higher than ever levels of efficiency and performance.

Following its introduction to the commercial marine sector in November 2023, the ammonia solution has undergone extensive testing to optimize its performance parameters. The latest results, assessed against the FuelEU Maritime reference and measured on both a Well-to-Wake and Tank-to-Wake basis, show that a 95 percent ammonia energy share now achieves up to a 90 percent reduction in greenhouse gas emissions compared to equivalent diesel engines. This represents a further 18 percent improvement on the solution's emissions performance.

The Wärtsilä 25 ammonia engine, which is available as part of the Wärtsilä 25 engine platform, was developed based on the company’s safety and operational experience gained from low pressure dual-fuel (DF) engines running on LNG. The recent tests have shown ammonia to be a suitable fuel for the low-pressure Otto cycle concept which is the design that Wärtsilä has utilised 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 greenhouse gas 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. Ammonia is also highly knock resistant, with robust combustion capabilities across a wide range of engine settings.

The enhancements made to the Wärtsilä 25 ammonia engine’s performance benefit the entire ammonia solution, which comprises of an AmmoniaPac fuel gas supply system, the Wärtsilä Ammonia Release Mitigation System (WARMS), and the Wärtsilä NOx Reducer (NOR) for optimal exhaust after-treatment. Safety, efficiency and reliability are central to the solution design, maximized by a highly sophisticated automation system and maintenance agreement to ensure safe and efficient onboard operations. Alongside future engine orders, the enhanced performance will also be integrated into engines already contracted as first deliveries are due to take place from 2026 onwards.

Ammonia has emerged as a promising alternative fuel as the shipping industry looks for more sustainable fuel options. With global regulations having set a clear destination for shipping – net zero emissions by mid-century – ammonia will play a significant role in enabling the shipping industry to reduce its emissions. A report from Wärtsilä highlights the role that sustainable fuels will play in achieving this target which is set by the International Maritime Organization (IMO). According to the report, existing decarbonization solutions, such as fuel efficiency measures, can cut shipping emissions by up to 27 percent; however, sustainable fuels, such as ammonia, will be a critical step in eliminating the remaining 73 percent.