The Role of Green Ammonia in Decarbonizing the Shipping Industry

The global shipping industry is at the beginning of one of the most significant technical and commercial transitions in its history. The International Maritime Organization’s 2050 net-zero greenhouse gas target has created an inescapable imperative: the fleet of approximately 55,000 ocean-going vessels that moves 90% of global trade must transition to fuels that produce no net carbon emissions. This transition is reshaping shipbuilding order books, port infrastructure planning, and energy supply chains — and green ammonia is one of the most compelling candidates to play a central role as the zero-carbon maritime fuel of choice for large ocean-going vessels.

Ammoniagas supplies green ammonia and conventional ammonia to industrial and maritime sector customers, tracking the rapidly evolving maritime fuel transition as a key driver of future ammonia demand.

1. The Shipping Industry’s Emissions Challenge

International shipping is responsible for approximately 2.5-3% of global greenhouse gas emissions — roughly equivalent to the total annual emissions of Germany. Unlike many other industrial sectors where decarbonisation pathways using electrification are well established, shipping presents unique challenges: vessels must carry their own energy supply for journeys lasting weeks; energy density is critical because every tonne of fuel carried reduces cargo capacity; and the global port network that refuels ships must be able to supply the chosen fuel at hundreds of locations worldwide.

The current primary marine fuel — heavy fuel oil (HFO) and its lower-sulphur variants — is a carbon-intensive residual product with no pathway to net-zero emissions. LNG, while lower in carbon than HFO, is still a fossil fuel that cannot meet a 2050 net-zero target. The industry requires genuinely zero-carbon fuels, of which the leading technical candidates are: green ammonia, green methanol, liquid hydrogen, and advanced biofuels. Each has different technical and economic characteristics that suit different vessel types and trade routes.

2. IMO Regulations Driving Zero-Carbon Fuel Adoption

The International Maritime Organization’s Revised GHG Strategy (2023) established the following emission reduction targets for international shipping:

• By 2030: At least 20% reduction in total GHG emissions versus 2008 baseline (striving for 30%)
• By 2040: At least 70% reduction versus 2008 baseline (striving for 80%)
• By 2050: Net-zero GHG emissions from international shipping

To support these targets, IMO introduced the Carbon Intensity Indicator (CII) framework from 2023, which annually rates each ship’s carbon intensity and requires improving ratings over time. Ships rated D or E in consecutive years face corrective action plans. This creates near-term financial pressure on fleet operators in addition to the longer-term 2050 imperative.

IMO is also developing a global fuel standard (Goal-Based Fuel Standard) and a market-based measure (pricing carbon intensity) expected to be adopted in the mid-2020s — these mechanisms would directly price the carbon disadvantage of HFO versus zero-carbon fuels, accelerating the economic case for ammonia and other alternatives.

3. Why Ammonia Is a Leading Zero-Carbon Fuel Candidate

Ammonia’s suitability as a maritime fuel rests on a combination of chemical, physical, and practical properties that compare favourably to other zero-carbon fuel options:

The combination of zero CO2 combustion, manageable liquefaction temperature, and the ability to leverage existing ammonia shipping and port infrastructure gives ammonia a practical advantage over liquid hydrogen for large ocean-going vessels. The primary disadvantage — toxicity — is manageable with appropriate engineering and crew training, though it represents a genuine challenge versus other fuel options.

4. Ammonia Combustion Technology for Ships

Ammonia presents specific combustion challenges that require engineering solutions beyond simply substituting it for conventional marine fuel. The key challenges are:

Flame speed: Ammonia’s laminar flame speed is approximately 7 cm/s — about one-sixth of natural gas flame speed. This lower flame speed can cause incomplete combustion and flame instability in conventional combustor designs. Solutions include: using ammonia-hydrogen blends (where on-board cracking of a portion of the ammonia provides hydrogen to accelerate flame speed); high-pressure injection; and modified combustor geometry designed specifically for ammonia flame characteristics.

NOx emissions: Ammonia combustion produces elevated NOx compared to natural gas combustion, because the nitrogen in the ammonia molecule becomes available to form NOx in the combustion reaction. Mitigation approaches include: optimised excess air ratios; staged combustion; and selective catalytic reduction (SCR) aftertreatment of exhaust gases — the same technology used in power plants and cement kilns for NOx control.

Pilot fuel: Most practical ammonia marine engine designs use a small amount of pilot fuel — diesel, methanol, or hydrogen — to initiate combustion, with ammonia as the primary fuel above a certain engine load. This simplified the ignition challenge while still achieving the majority of CO2 reduction.

5. Engine Development Programs

Major marine engine manufacturers have made significant investments in ammonia-capable engine development:

MAN Energy Solutions: Has developed a dual-fuel two-stroke ammonia engine design (ME-LGIP adapted for ammonia) targeting large ocean-going vessels including bulk carriers, tankers, and container ships. Engine designs are available for licensing by shipyards, with first deliveries of ammonia-fuelled vessels using MAN engines expected from the late 2020s.

WinGD: Has developed the WinGD X-DF-A dual-fuel ammonia engine for large vessels, targeting similar markets as MAN. The engine uses a diesel pilot injection system for stable ammonia ignition.

Wärtsilä: Has developed four-stroke dual-fuel ammonia engine concepts targeting medium-speed applications including ferries, RoPax vessels, cruise ships, and offshore vessels. Ammonia fuel cell integration for auxiliary power is also under development.

In addition to main engine development, several companies are developing ammonia fuel cell systems for ships — solid oxide fuel cells in particular can directly convert ammonia to electricity at higher efficiency than combustion, and are suited to smaller vessels and auxiliary power applications.

6. Safety Challenges and Solutions

Ammonia’s toxicity is the most significant barrier to its adoption as a maritime fuel — not an insurmountable one, but one that requires substantial engineering investment and crew training well beyond conventional bunker fuel handling. Ammonia is classified as a toxic industrial gas (Class 2.3 under IMDG Code), with an IDLH (immediately dangerous to life and health) concentration of 300 ppm. A significant leak aboard a vessel could incapacitate crew members rapidly.

The engineering solutions being developed for ammonia-fuelled vessels include: fully enclosed fuel supply systems with no open connections in crew-accessible spaces; ammonia gas detection in all fuel system compartments with automatic shut-off on detection; positive pressure ventilation in fuel-handling spaces to prevent ammonia accumulation; emergency scrubber systems to capture ammonia from relief valve discharges; and remotely operated emergency isolation valves on all ammonia fuel system connections.

Crew training requirements for ammonia-fuelled vessels will be substantially higher than for conventional fuel. IMO’s Maritime Safety Committee is developing specific training and competency standards for crews serving on vessels using alternative fuels including ammonia — these standards are expected to be incorporated into the STCW (Standards of Training, Certification and Watchkeeping) framework.

7. Bunkering Infrastructure Development

The commercial viability of ammonia as a maritime fuel depends critically on the development of bunkering infrastructure at key port hubs. Vessels that cannot refuel ammonia at their destination ports are operationally limited — and no shipping operator will commit to an ammonia-fuelled newbuild if they cannot be confident about fuel availability on their trade routes.

The leading ports developing ammonia bunkering capability include: Rotterdam (the largest European port, where Yara and Shell have active ammonia bunkering development projects); Singapore (the world’s largest bunkering port, where MPA — the Maritime and Port Authority — has been actively developing alternative fuel frameworks); and ports in Japan and South Korea that are investing in combined ammonia import and bunkering infrastructure. Several Middle Eastern ports with existing ammonia export terminals are also well positioned to add bunkering services.

India’s major ports — JNPT, Mundra, Hazira, Visakhapatnam — are evaluating ammonia bunkering as part of broader green port development strategies, potentially positioning India’s west coast ports on the trade routes linking Middle East green ammonia producers with East Asian importers.

8. Shipping Company Initiatives

The transition to ammonia fuel is being driven by a combination of regulatory pressure and voluntary corporate sustainability commitments. Key shipping company positions include:

• Multiple major container lines and bulk carriers have included ammonia-ready vessel specifications in recent newbuild orders, allowing future fuel system conversion even if initial operation uses LNG or conventional fuel.
• Several ammonia carrier vessels — ships designed to transport ammonia cargo — are being designed with dual-fuel capability, using their own cargo as fuel for the vessel’s engines, dramatically improving the economics of the ammonia carrier business.
• Industry consortia including the Getting to Zero Coalition and the Ammonia Energy Association are coordinating investment and advocacy across shipping companies, fuel producers, port operators, and regulators to accelerate the development of the ammonia fuel ecosystem.

9. Impact on Global Ammonia Demand

The shipping fuel application represents a potential step-change in global ammonia demand. Current global ammonia production is approximately 180 million tonnes per year, of which 15-20 million tonnes enter seaborne trade. The maritime fuel market for ammonia, if adoption progresses according to optimistic industry scenarios, could add 30-50 million tonnes per year by 2040-2050 — effectively doubling the size of the global ammonia market from its current base.

Even under more conservative scenarios, the maritime fuel application adds a new category of high-value demand for green ammonia that will shape investment decisions across the entire ammonia supply chain — from renewable energy generation and electrolyser deployment to port infrastructure and shipping fleet composition. Indian ammonia producers who position for this market now, by developing green ammonia production and export capabilities, stand to benefit from what may be the largest new industrial market to emerge in the global energy transition.

10. India’s Position in Maritime Green Ammonia

India’s strategic interest in maritime green ammonia is both as a future fuel supplier and as an active participant in the transition within its own domestic shipping sector. India operates a significant merchant fleet and has several major port developments underway that could integrate green ammonia bunkering infrastructure.

On the supply side, India’s National Green Hydrogen Mission creates the policy framework for green ammonia production at the scale needed to supply maritime markets. Green ammonia transporters in India and state-level exporters across Gujarat, Maharashtra, Tamil Nadu, and Andhra Pradesh are developing the domestic logistics capabilities that will underpin export supply to the maritime fuel market.

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