The commercialisation of ammonia as a marine fuel has long been contingent on engine availability. Without certified, commercially available engines capable of running on ammonia at the power outputs required for ocean-going vessels, shipowners had no mechanism to make credible fuel-switching commitments regardless of their intentions. That dependency has now been largely resolved. Through 2025, the three manufacturers that dominate the deep-sea marine engine market — MAN Energy Solutions, WinGD, and Wärtsilä — each progressed ammonia-capable engines to commercial deployment phase.
The three approaches are technically distinct, serve different vessel types, and carry different implications for the NOx management challenge that ammonia combustion presents. Understanding the differences matters for shipowners, charterers, and port authorities navigating what is rapidly becoming a multi-fuel shipping environment.
MAN Energy Solutions: the two-stroke pathway
MAN Energy Solutions is the licensor of the two-stroke, low-speed diesel engine technology that powers the majority of the world's large ocean-going vessels — container ships, bulk carriers, and tankers in the Capesize to VLCC range. Its ME-LGIA dual-fuel ammonia engine programme has been in development since 2019, with extensive testing at the company's Copenhagen research facility.
The first commercial deployment of the MAN B&W two-stroke ammonia engine is a 7S60ME unit being built by Mitsui E&S in Japan for installation in a Newcastlemax bulk carrier, a joint venture between K Line, Nihon Shipyard, and Itochu. The vessel is expected to be delivered in 2026. Prior to commercial sales release, MAN ES is running parallel pilot projects in South Korea, China, and Japan to gather operational data and crew experience — a cautious approach that reflects both the safety requirements of ammonia handling and the company's awareness that engine performance data from live vessels will be the most credible evidence base for broader adoption.
The MAN B&W ME-LGIA engine operates as a dual-fuel design, capable of running on either conventional fuel oil or ammonia. At sea, this provides operational flexibility; at the transition stage, it reduces the risk for owners whose bunkering access to ammonia is not yet fully assured.
The central technical challenge for MAN ES's two-stroke design — and for all direct combustion ammonia engines — is NOx management. Ammonia combustion produces significant quantities of nitrous oxide (N2O), a greenhouse gas approximately 273 times more potent than CO2 over a 100-year period, and nitrogen oxides (NOx) that are subject to MARPOL Tier III emission limits in emission control areas. MAN ES has addressed this through a selective catalytic reduction (SCR) system, the first unit of which was delivered from China in early 2025. The effectiveness of the SCR system under real-world operating conditions — variable engine loads, cold starts, port manoeuvring — is one of the data points that the pilot programme is designed to provide.
WinGD: dual-fuel for bulk carriers
WinGD, the Swiss engine developer majority-owned by China State Shipbuilding Corporation (CSSC), has pursued a parallel development track with its X-DF-A dual-fuel ammonia engine platform. The X72DF-A units — designed for large bulk carriers in the Newcastlemax and Capesize range — are being fitted in a series of 210,000 DWT vessels being built at Qingdao Beihai Shipyard in China. Commercial deployment commenced in June 2025.
WinGD's relationship with CSSC gives it a direct route to the world's largest shipbuilding market, a structural advantage that is particularly significant given China's dominant share of current global newbuild orderbook. Singapore-based shipping company AET has ordered WinGD X-DF-A engines for Aframax tankers being built in China, establishing the technology's applicability beyond bulk carriers. Eastern Pacific Shipping's ammonia-powered Newcastlemaxes, under construction at Qingdao Beihai, are expected to be delivered from 2026 onwards.
Fortescue, the Australian iron ore and green energy company, has a Newcastlemax vessel under construction with a WinGD X-DF-A engine, expected for delivery by end of 2026. The vessel is notable because it will operate on the Pilbara to East Asia iron ore corridor — precisely the route where ammonia bunkering infrastructure is being developed in both Australia and northeast China, creating a test bed for the full supply chain in one of the world's highest-volume shipping corridors.
Wärtsilä: the four-stroke offering for smaller vessels
Wärtsilä's approach to ammonia combustion addresses a different segment of the maritime market. The company's Wärtsilä 25 ammonia engine — a four-stroke, medium-speed design — targets smaller vessels including coastal tankers, fishing vessels, ferries, and offshore support vessels, where the power-to-weight characteristics of four-stroke designs are preferable to the large, slow-rotating two-stroke engines that dominate ocean-going vessels.
Wärtsilä declared commercial availability of the Wärtsilä 25 ammonia engine during 2025, following extensive testing that demonstrated up to 90% greenhouse gas emission reductions compared to conventional diesel operation. The company has orders from fishing vessel operators Vardin and Framherji for ammonia-fuelled trawlers to be deployed in the Faroe Islands — a market where the regulatory environment and community expectations around decarbonisation have moved faster than the global average.
Wärtsilä has also supplied the ammonia fuel supply and cargo handling systems for a series of EXMAR dual-fuel vessels built in South Korea, and has developed a dedicated ammonia leak safety monitoring system for continuous onboard ammonia detection — a product that reflects the company's recognition that crew safety systems will be as important to adoption as engine performance.
The NOx problem and why it matters
Across all three manufacturers, the NOx and N2O challenge is the least-resolved technical issue in ammonia marine combustion. The well-to-wake greenhouse gas profile of ammonia fuel — its primary advantage — is highly sensitive to N2O emissions during combustion. If slip and incomplete combustion result in significant N2O release, the climate benefit of switching from fossil fuels is substantially reduced and could, in worst-case scenarios, be eliminated. The actual N2O emissions performance of the deployed engines under real operating conditions is not yet publicly reported at sufficient detail to resolve the uncertainty.
The IMO's well-to-wake emissions accounting framework, under development as part of the Net Zero Framework process, will determine how N2O emissions from ammonia combustion are counted in the regulatory context. Until that framework is finalised, shipowners operating ammonia-fuelled vessels face uncertainty about the regulatory value of their fuel choice.
What this means for shipowners
The commercialisation of ammonia engines by all three major manufacturers removes one of the principal objections to ammonia as a credible marine fuel. The remaining objections — bunkering infrastructure, price competitiveness relative to conventional fuels and methanol, crew training, and regulatory uncertainty — are real and will constrain adoption in the near term. But the conversation has shifted from whether ammonia-capable engines exist to whether the conditions for their deployment can be assembled.
For shipowners placing orders today for vessels with delivery dates in 2028 to 2030, the engine choice is increasingly a genuine commercial decision rather than a speculative one. The Observatory will track vessel deliveries and operational data from the first deployed ammonia-fuelled ships through 2026, with particular attention to the NOx and N2O performance data that will determine the real-world climate benefit of the fuel switch.