26 May 2025

Technology group Wärtsilä has once again pushed the envelope in marine propulsion technology with its latest improvements to a 4-stroke engine-based solution for ammonia fuel. Following its commercial introduction in November 2023, extensive testing has led to even higher efficiency and enhanced performance parameters—achieving up to a 90 percent reduction in greenhouse gas emissions compared to comparable diesel engines when operating with a 95 percent ammonia energy share. This marks an 18 percent improvement over previous emissions performance metrics.

A Strategic Shift Toward Sustainable Maritime Fuels

Ammonia has emerged as one of the most promising alternative fuels as the maritime sector grapples with stringent global decarbonization targets. With the International Maritime Organization (IMO) setting a clear pathway toward net zero emissions by mid-century, shipping companies face an imperative to overhaul traditional fuel sources. While conventional measures—such as enhanced fuel efficiency—can reduce emissions by up to 27 percent, sustainable fuels like ammonia are essential for eliminating the remaining 73 percent of emissions.

Wärtsilä’s progressive approach is part of a broader industry trend. As the demand for lower-carbon operations intensifies, shipping firms increasingly turn to innovative technologies that promise both environmental benefits and operational reliability.

Deep Roots in Marine Innovation

Headquartered in Finland, Wärtsilä has a storied history spanning over 180 years in power solutions and marine engineering. Its marine business is a global leader, renowned for pioneering advanced propulsion systems, automation, and integrated energy solutions across a diverse fleet of vessels. Central to its success is the company’s legacy in dual-fuel solutions—particularly in low-pressure engines running on LNG—which has provided critical insights into fuel flexibility, safety, and performance.

Building on that expertise, the new Wärtsilä 25 ammonia engine was designed as part of the Wärtsilä 25 engine platform. Drawing from the extensive operational and safety experience of its LNG dual-fuel systems, Wärtsilä opted for the low-pressure Otto cycle. This design was chosen for its superior safety, efficiency, and greenhouse gas reduction potential, and it has now been validated through rigorous testing on both Well-to-Wake and Tank-to-Wake bases.

Technical Breakthroughs and Key Enhancements

The latest test results have confirmed that the low-pressure Otto cycle concept can deliver fuel efficiencies on par with existing dual-fuel LNG engines. Moreover, ammonia—known for its high knock resistance—demonstrates robust combustion characteristics across a wide range of operating conditions. As a result, the Wärtsilä 25 ammonia engine now sets a new benchmark in emissions reduction, meeting and exceeding the industry’s stringent requirements.

Stefan Nysjö, Vice President of Power Supply at Wärtsilä Marine, elaborates:

“With decarbonisation at the forefront of our strategy, we have continuously enhanced our ammonia engine solution – integrating additional safety features and refining its performance. By choosing the low-pressure Otto cycle, we are confident that our solution delivers unmatched safety, efficiency, and reliability for our customers.”

 

Beyond the engine itself, Wärtsilä’s comprehensive ammonia solution encompasses critical auxiliary systems:

• AmmoniaPac Fuel Gas Supply System: Ensures precise fuel management.

• Wärtsilä Ammonia Release Mitigation System (WARMS): Enhances onboard safety.

• Wärtsilä NOx Reducer (NOR): Provides optimal exhaust after-treatment.

Supported by a sophisticated automation system and backed by robust maintenance agreements, this integrated solution guarantees safe and efficient operations across Wärtsilä’s fleet. The enhanced performance will not only benefit future engine orders but will also be rolled out to engines already contracted, with first deliveries scheduled from 2026 onward.