28-05-2025
Wärtsilä's 4-stroke ammonia engine tests reduce GHG emissions by up to 90%
Wärtsilä has announced the results of extensive testing of its 4-stroke ammonia engine, which demonstrated a reduction in greenhouse gas (GHG) emissions by up to 90% compared to traditional diesel engines.
After its debut in the commercial marine sector in November 2023, the 4-stroke engine-based solution for ammonia fuel has been rigorously tested by the company to optimise its performance parameters.
The latest results were evaluated against the FuelEU Maritime reference and measured on both Well-to-Wake and Tank-to-Wake calculations.
Wärtsilä said the engines can achieve up to a 90% reduction in GHG emissions compared to an equivalent diesel engine when run on a 95% ammonia fuel mix.
The Wärtsilä 25 ammonia engine was developed with the company's safety and operational expertise acquired from its experience with low-pressure dual-fuel (DF) engines that operate on LNG.
Wärtsilä explained that recent tests have demonstrated ammonia to be an effective fuel for the low-pressure Otto cycle concept, also used for its ammonia engine solution.
Wärtsilä's decision to use a low-pressure Otto cycle was influenced by various factors, such as safety, efficiency, and the potential for reducing GHG emissions, among other considerations, it explained.
Extensive testing on various engine sizes has revealed that the efficiency of the low-pressure Otto cycle is comparable to that of dual-fuel LNG engines, it added. Ammonia has high knock resistance and maintains 'robust' combustion performance across a diverse range of engine settings.
Wärtsilä Marine vice president of power supply Stefan Nysjö said: 'With decarbonisation front and centre of our company strategy, we have continued to enhance the capabilities of our ammonia engine solution - adding even more safety features and further improving its performance.
'This is in line with our commitment to 'continuous improvement', whereby we continue to develop, test and enhance new and current technologies and solutions which will support the industry in making meaningful reductions in greenhouse gas emissions. For our ammonia engine we opted for the low-pressure Otto cycle concept as we are confident this will deliver the best levels of safety, efficiency and reliability for our customers.'
The improvements to the performance of Wärtsilä 25 ammonia engine are claimed to benefit the entire ammonia solution, which includes the AmmoniaPac fuel gas supply system, the Wärtsilä Ammonia Release Mitigation System (WARMS), and the Wärtsilä NOx Reducer (NOR) for optimal exhaust after-treatment.
The improved engine performance will be incorporated into future orders and engines already contracted, with first deliveries expected from 2026.
According to a report released by Wärtsilä in March last year, the current decarbonisation strategies, such as improving fuel efficiency measures, have the potential to reduce shipping emissions by up to 27%. However, to address the remaining 73%, the adoption of sustainable fuels, such as ammonia, will be essential.
This month, Wartsila Gas Solutions, a business unit of Wartsila, secured a contract to supply cargo handling systems for two very large ammonia carriers (VLACs) being built at the Hanwha Ocean shipyard in South Korea for a Japanese shipping company.
"Wärtsilä's 4-stroke ammonia engine tests reduce GHG emissions by up to 90%" was originally created and published by Ship Technology, a GlobalData owned brand.
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