Ammonia as fuel by Wärtsilä

Ammonia as marine fuel? It is easier if you do it smart

Adopting ammonia to fuel ships can decrease greenhouse gas emissions. How will it work? How to get started? Here’s how to be smarter about ammonia as marine fuel.

Ammonia has emerged as a promising alternative as the shipping industry looks for more sustainable fuel options. This article explores the many sides of using ammonia as a marine fuel and provides insights on how to do it smart.

To meet the IMO’s target of net-zero greenhouse gas emissions by 2050, the shipping industry needs to move to cleaner fuels. There is no clear frontrunner among the several potential options, but ammonia offers some unique benefits that make it a leading contender. 

  • It doesn’t produce CO2, sulphur or particulate emissions when combusted.
  • A supply chain and infrastructure already exist for other applications.
  • It can be produced using renewable energy sources.
  • It is relatively easy to store and handle onboard ships.

But is it the right solution for your vessel? Read on to find out, or use these shortcuts to take you directly to the topics you’re keen to read more about:


All about ammonia

What is ammonia?

Ammonia is a colourless gas with a powerful odour. It is commonly used in cleaning products, refrigeration systems and fertilisers. It has emerged as a promising alternative fuel for the maritime industry because it has significant potential to reduce greenhouse gas emissions.

Although ammonia has many benefits, it also has some drawbacks, such as its toxicity and flammability.

How is ammonia produced?

Nitrogen and hydrogen gases are combined under high pressure at a high temperature in the presence of a catalyst. This reaction produces ammonia gas.

What is brown or grey ammonia?

Ammonia has traditionally been produced using natural gas or even coal as the energy source. Because this process produces significant carbon emissions, the result is called grey ammonia, or sometimes brown ammonia.

What is blue ammonia?

When carbon capture is added to the ammonia production process, it reduces the carbon emissions and results in blue ammonia.

What is green ammonia?

Green ammonia is produced using renewable energy sources, such as wind or solar power. Using ammonia as a fuel will only reduce overall greenhouse gas emissions if it is green ammonia. There is growing interest in producing green ammonia fuel.


Ammonia and the environment

Is ammonia environmentally friendly?

Ammonia releases no CO2 when combusted, so it has great potential to be a more sustainable fuel choice. But as far as overall well-to-wake emissions are concerned, only green ammonia will bring significant environmental benefits. In fact, green ammonia is completely carbon-free whether the resulting emissions are considered from tank-to-wake or from well-to-wake. 

On the other hand, producing grey ammonia generates one third more carbon emissions from well to wake than heavy fuel oil. 

In the future engines will be able to run on 100% ammonia and use biodiesel as pilot fuel, enabling a fully sustainable solution.

What are the greenhouse gas emissions from ammonia? How can we deal with them?

Ammonia is used in traditional selective catalytic reduction (SCR) systems to capture NOx emissions. Today the reagent is urea because it is safe and easy to handle, but in the future we will see ammonia used as the reagent, though probably initially backed up by urea.

How we handle emissions abatement in the future and the reagents we use in SCR systems will very much depend on the engine combustion concept that emerges as the frontrunner. 

Catalysts for eliminating ammonia slip from the reagent in the SCR process are already used in projects in the US where strict emission limits apply. Such projects provide a very good starting point for developing catalyst setups that are optimised for maritime applications. 


Ammonia as a marine fuel 

Is ammonia a viable fuel? Can ammonia be used as fuel?

Ammonia is an attractive alternative to fossil fuels for the shipping industry. It has the potential to significantly reduce greenhouse gas emissions, but there are still challenges to overcome. These include the development of a reliable ammonia fuel bunkering network and the fact that ammonia engines need additional maintenance because of the fuel’s corrosive nature.

Ammonia can be used as a gaseous or liquid fuel. Engines can burn this fuel well with minor adaptations.

Handpicked related content: Want to know more about future fuels in shipping? Find out more about the options available.

What is ammonia’s fuel efficiency?

When it comes to ammonia fuel efficiency, the bottom line is it has a lower volumetric efficiency and energy density than diesel. Ammonia engines also have a lower efficiency than traditional fossil fuel engines. In short, a ship that uses ammonia needs much higher fuel storage capacity. The volume and weight of the storage infrastructure required also has a significant impact on the vessel’s operating range.

What are the main challenges when using ammonia to fuel ships?

There are three main challenges when using ammonia to fuel ships:

  • Ammonia is toxic, so the safety of the whole vessel must be considered, including the ventilation systems. 
  • When using ammonia, ships will need larger fuel storage capacity compared to diesel or LNG because ammonia has a lower volumetric energy density than both of these fuels.
  • Because ammonia is a new fuel, the regulatory landscape is still under development.

What are the advantages of ammonia as a marine fuel?

One of ammonia’s biggest advantages is that it doesn’t contain any molecular carbon, so when it’s combusted in an engine it produces no CO2 emissions. Adopting green ammonia as a maritime fuel is a great way to decarbonise shipping, helping to reduce the reliance on fossil fuels and move towards a more sustainable future.

Ammonia is abundant and can be produced using renewable energy sources such as wind and solar power. It is widely manufactured and traded, primarily for use in the production of fertilisers, and has the energy potential to be a viable marine fuel. 

Fuel storage and delivery systems don’t need to be overly complex when ammonia is used in its liquid form. This reduces the operating costs. 

Ammonia is already being used as fuel in power generation. 

What are the disadvantages of ammonia as a marine fuel?

Because ammonia is highly toxic and corrosive it requires careful handling and storage. However, the risks can be mitigated with proper crew training and equipment such as protective gear and ventilation systems. 

Ammonia doesn’t produce CO2 when combusted as fuel. The NOx emissions it produces can be handled with an abatement solution, and a wet scrubber system might be needed to manage potential ammonia gas releases. More investigation into these solutions, with the cooperation of classification societies, is needed.

One of the biggest unknowns with ammonia is how to handle potential N2O emissions. Catalysts are being developed for N2O – a potent greenhouse gas – to minimise N2O emissions and make ammonia a sustainable solution. For example, the Wärtsilä 25 ammonia solution with its optimised combustion and integrated aftertreatment has been designed to minimise all greenhouse gas emissions. 

For a quick overview, you can download a handy one-page guide on ammonia as marine fuel: Ammonia – Alternative fuels quick guide


Ammonia marine fuel safety 

How can ammonia be used safely as a marine fuel?

Ammonia has several safety issues related to toxicity, explosion risk and odours. Regulations are currently being developed to ensure ammonia can be used safely as a maritime fuel.

Three considerations are important to remember when it comes to ammonia fuel safety:

  • Ammonia is highly toxic and can be dangerous if not handled properly.
  • Ammonia requires specialised storage and handling equipment.
  • Ammonia fuel systems must be designed with safety in mind.

Wärtsilä is collaborating closely with classification societies to identify protocols and technologies to ensure ammonia is safe to use as a maritime fuel. 

How can an ammonia leak be detected?

Ammonia is a toxic gas that can cause serious health problems if inhaled. It can also be flammable and explosive in certain conditions. Handheld or mounted sensors – or even just the smell – are the best forms of leak detection.

Ammonia leaks are not simple to handle because the gas is toxic and cannot be vented into the surrounding atmosphere. However, a leak will not affect the ship’s operation because the engine can switch to using the other main fuel. 

Why should ammonia fires be suppressed with CO2 and not water?

Water can react with ammonia and form chloramine, which is a toxic gas. Carbon dioxide (CO2) should be used to extinguish ammonia fires so that no harmful gases are formed. 

How toxic is ammonia?

If you can smell ammonia, it means there is a leak. Depending on the concentration, it can also mean there is a health risk. 

At low levels, ammonia can cause eye, nose and throat irritation. At high levels, it can cause more serious health problems. It is important to evacuate the area immediately if there is a leak and seek medical attention if you experience any symptoms.

Ammonia presents an explosion risk when its concentration in air reaches 15–28 vol.%. 
The risk of ammonia toxicity has been defined according to acute exposure guideline levels (AEGLs).

  • AEGL-1 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic non-sensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.
  • AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.
  • AEGL-3 is the airborne concentration, expressed as parts per million (ppm) or milligrams per cubic meter (mg/m3), of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.

The following table shows the ammonia AEGLs for five exposure periods.


10 min

30 min

1 hour

4 hours

8 hours


30 ppm

30 ppm

30 ppm

30 ppm

30 ppm


220 ppm

220 ppm

160 ppm

110 ppm

110 ppm


2,700 ppm

1,600 ppm

1,100 ppm

550 ppm

390 ppm


Ammonia and compliance

What are the regulations governing ammonia as marine fuel?

Regulatory frameworks for the development of ammonia as a marine fuel are still being developed. Collaboration with ship owners and operators is critical to give them confidence in the solutions being developed.


Ammonia availability 

Is ammonia available as fuel for ships?

There isn’t yet much ammonia available for shipping as there is strong competition for ammonia as a fuel. The shipping industry is competing with the fertiliser and energy industries, and ramping up production takes time. Building and commissioning an ammonia plant can take anywhere from four to six years. However, more than 200 low-carbon ammonia facilities are currently being planned globally. 

Are ammonia fuel engines available?

Wärtsilä introduced the marine sector’s first commercially available 4-stroke engine-based solution for ammonia fuel in November 2023. It is now available as part of the Wärtsilä 25 engine platform.

Which ammonia solutions are ready?

In addition to the Wärtsilä 25 engine platform, Wärtsilä’s solution for ammonia fuel includes the: 

  • AmmoniaPac fuel gas supply system 
  • Wärtsilä Ammonia Release Mitigation System (WARMS)
  • Wärtsilä NOx Reducer (NOR) for optimal exhaust aftertreatment. 

The solution also includes: 

  • a sophisticated automation system and maintenance agreement to ensure safe and efficient onboard operations
  • dedicated training for the crew
  • 24/7 global support 

The Wärtsilä solution for ammonia fuel has been designed to ensure smooth and safe adoption of ammonia as a new fuel.

Working with a single manufacturer to design, integrate and supply the necessary components and systems makes for a safer solution and more efficient process.


Learn more about the Wärtsilä ammonia solution and how significant and immediate the reduction of emissions can be when running on sustainable ammonia.

Access Wärtsilä Ammonia Lounge

Operational considerations for ammonia 

How can I make ammonia operations happen?

To move to ammonia-based operations your vessel needs to be designed to use ammonia. It might also be possible to retrofit an existing vessel, but there may be challenges to find space for equipment such as ammonia tanks. The fuel gas supply system needs to be designed for ammonia, and this includes a lot of different components.

You will also need an ammonia fuel engine, either one specifically developed for ammonia use or a retrofitted engine that can run on ammonia. A fuel-flexible and easily upgradable engine like the Wärtsilä 25 will be beneficial if you are considering running on ammonia in the future.

Your vessel’s aftertreatment system needs to be adapted according to the fuel it is using. Depending on whether your engines will be running on liquid or gaseous ammonia, you may also require some additional equipment such as a high-pressure room for the pumps if a high-pressure system is used to inject the ammonia fuel into the engine.

What do I need to consider when adopting ammonia as marine fuel? 

As the shipping industry moves towards decarbonisation, ammonia is emerging as a promising alternative fuel. To transition, your engine needs to be designed to use ammonia and specific materials need to be used for the components that will be exposed to the fuel. Using ammonia as marine fuel also requires significant changes in the engine room and the fuel-handling system. 

When building a new vessel, it is critical to consider what is needed to use ammonia as a fuel during the design phase. From a retrofit perspective, in order to safely bunker, handle and burn ammonia onboard, some of the existing vessel structures will have to be changed. New structures will need to be designed, assembled and built to create the necessary space to store ammonia onboard and transfer it to the converted engines. Auxiliary systems will need to be arranged to guarantee safely levels required by applicable rules and regulations. New auxiliary systems may also be needed, for example a drain system, bilge system, nitrogen system and ventilation system.

What are the major changes needed in the engine room?

To ensure safety and compliance with regulations, it is important to follow best practices and guidelines for handling ammonia. Proper handling of ammonia in an engine room requires careful consideration of the following questions, among others:

  • How should ventilation be handled? Forced ventilation is required to ensure ammonia vapours do not accumulate in the engine room.
  • What are the best practices for detecting ammonia fuel leaks? Handheld or mounted sensors should be used.
  • How can I prevent an ammonia explosion? Ammonia presents an explosion risk when its concentration in air reaches 15–28 vol.%. Explosion vents are required to prevent pressure build-up if ammonia is released into the engine room.
  • How can I put out an ammonia fire? Carbon dioxide (CO2) should be used to extinguish an ammonia fire.
  • Where in the ship should the ammonia tanks be located? The tanks for storing ammonia should be located above deck to prevent any leaks from entering the engine room. 

Adopting ammonia as marine fuel will require significant changes in the engine room, the fuel handling system and potentially the exhaust gas after-treatment system. However, with proper precautions and safety measures, ammonia can be a safe and sustainable alternative to traditional marine fuels.


How should the crankcase door be opened after the engine has run on ammonia?

When opening the crankcase door after the engine has run on ammonia, make sure to wear appropriate personal protective equipment and follow the engine manufacturer’s service and maintenance instructions.


The future of ammonia

Is ammonia the fuel of the future?

Because ammonia has the potential to be carbon free from production to combustion, it has a lot of promise as a future fuel, especially for newbuild vessels. However, the additional space required to store and handle ammonia may mean that it is not a viable retrofit option for smaller vessels like tugs and fishing vessels. 

Ammonia has already been trialled in fuel-cell solutions and in four-stroke ammonia engines. Whether ammonia becomes the dominant fuel of the future will depend on numerous factors, including technological advances, regulatory support and fuel supply investments. Zero-carbon fuels such as green ammonia will play a big role in making maritime transportation more sustainable.

What will the ammonia fuel bunkering network look like?

The availability of ammonia as marine fuel, especially green ammonia, will be essential for reaching the marine industry’s decarbonisation targets. We are starting to see more discussions and investment decisions about an ammonia fuel bunkering network. This will scale up as the market starts to adopt ammonia.

Today, the demand for ammonia is mainly driven by fertiliser consumption, but the demand from the marine industry will start to increase as more vessels run on ammonia. DNV predicts ammonia use in shipping will be 170 PJ (1% of the shipping fuel mix) in 2030, 1,900 PJ (13% of the fuel mix) in 2040, and 5,000 PJ (36% of the fuel mix) in 2050.

The ammonia bunkering system can be fixed or mobile. Fixed bunkering involves stationary infrastructure at ports or fuelling stations, while mobile systems use transportable tanks. Ammonia can be stored as a liquid or a gas depending on the temperature or pressure.

Safety measures and environmental considerations play a critical role in the deployment of bunkering systems. 

Want to know more?

As the shipping industry seeks to reduce its carbon footprint, alternative fuels such as ammonia are becoming increasingly important. While there are challenges to be overcome, the potential benefits of using ammonia as marine fuel are significant.

By investing in the development of a reliable ammonia fuel bunkering network and continuing to improve ammonia engine technology, we can work towards a more sustainable future for the shipping industry.

If you’re interested in learning more about how ammonia could be part of your decarbonisation strategy, Wärtsilä offers a simple three-step approach with Wärtsilä Decarbonisation Services.


Wärtsilä Technical Journal, Vol. 2, 2021
International Maritime Organization (IMO) guidelines on the use of ammonia as marine fuel

Written by
Amanda Thurman

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