Validated in real-world trials, Wärtsilä’s ammonia engine delivers efficiency on par with LNG-powered systems, while achieving a 90% reduction in greenhouse gas emissions compared to traditional diesel engines.
Technology group Wärtsilä has announced a major milestone in its journey to decarbonise maritime transport: the successful extensive testing of its 4-stroke ammonia engine has demonstrated a greenhouse gas emissions reduction of up to 90% compared to traditional diesel engines. The results show significant progress in performance and efficiency since the engine’s initial release to the commercial marine market in November 2023.
The recent test results—assessed according to FuelEU Maritime reference points and measured on both Well-to-Wake and Tank-to-Wake bases—confirm that an engine operating with a 95% ammonia energy share can now achieve a 90% GHG reduction. This marks a further 18% improvement in emissions performance from Wärtsilä’s earlier benchmarks.
Advanced Engineering with Proven Safety and Performance
The Wärtsilä 25 ammonia engine, part of the modular Wärtsilä 25 engine platform, is the core of this innovative solution. It has been developed using Wärtsilä’s decades of experience in low-pressure dual-fuel (DF) LNG engines. The company chose a low-pressure Otto cycle combustion concept for the ammonia engine, citing advantages in safety, efficiency, and GHG reduction potential.
Test results show the Otto cycle-based design is well-suited to ammonia combustion, maintaining efficiency levels on par with Wärtsilä’s DF LNG engines. Moreover, ammonia’s high knock resistance and stable combustion performance across a wide range of engine settings further support its suitability as a sustainable marine fuel.
“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,” said Stefan Nysjö, Vice President of Power Supply at Wärtsilä Marine.
“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 with 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.” said Stefan Nysjö.
An Integrated, Turnkey Ammonia Solution
The Wärtsilä 25 ammonia engine is a key component of a full turnkey ammonia fuel solution that includes:
- AmmoniaPac – the integrated fuel gas supply system,
- Wärtsilä Ammonia Release Mitigation System (WARMS) – for enhanced safety and environmental control,
- Wärtsilä NOx Reducer (NOR) – for optimal emissions after-treatment.
This complete solution is engineered for maximum safety, reliability, and operational efficiency, supported by Wärtsilä’s sophisticated automation platform and comprehensive maintenance agreements. The improved performance metrics will be applied not only to future engine orders, but also retroactively to engines already under contract, with first deliveries expected in 2026.
Ammonia’s Role in a Decarbonised Future
Ammonia is gaining momentum as a leading alternative fuel in the maritime sector, offering zero-carbon combustion potential when produced from renewable sources. As the industry races to align with the International Maritime Organization’s (IMO) goal of net-zero emissions by 2050, sustainable fuels like ammonia are critical.
A recent Wärtsilä report underscores this shift, highlighting that while energy efficiency measures can reduce maritime emissions by up to 27%, the remaining 73% must be addressed through clean fuel adoption. The Wärtsilä 25 ammonia engine is poised to play a significant role in this transformation.
About Wärtsilä Marine
Wärtsilä Marine is a global leader in power, propulsion, and lifecycle solutions for the maritime industry. With a deep portfolio that includes marine engines, propulsion systems, hybrid technologies, exhaust treatment, and digital innovations, Wärtsilä is committed to driving the maritime transition to decarbonised operations. Their integrated approach spans performance-based agreements, lifecycle support, and digital ecosystems connecting vessels and ports.
About Wärtsilä
Wärtsilä Corporation is a global technology leader serving the marine and energy sectors. With a workforce of 18,300 professionals across 77 countries, Wärtsilä recorded EUR 6.4 billion in net sales in 2024. The company focuses on sustainable innovation to improve the environmental and economic performance of its global clientele. Wärtsilä is listed on Nasdaq Helsinki.
Source Wartsila Marine