AMMONIA AS A FUEL DIVIDES OPINION AS FIRST MOVERS PROCEED

The cost of green ammonia is expected to be higher than the fuels in use today, and as ammonia has a low cetane number, it requires an ignition source which will eventually need to be carbon neutral or carbon free.

René Sejer Laursen, ABS Director – Fuels & Technology, Global Sustainability, says the simplest option for incorporating ammonia as a fuel is to use a dual-fuel ammonia engine. “By combining biodiesel with green ammonia 100% neutrality can be reached. DME is produced from methanol which itself can also be produced solely from renewables. Instead of using diesel to ignite the ammonia, an ignition improver can be added in the form of DME, which will improve its ability to self-ignite without the use of pilot fuel. Using a diesel cycle engine to burn this mixture will require very few modifications to the engine system.”

DME is a good ignition improver since it has a cetane number of 60, he says, and DME and ammonia are fully mixable and can be stored in the same tank system that contains ammonia. This mixture has already been lab-tested on a small engine operating around 1,000rpm with good results, so using it in large bore engine operating at 70-100rpm will leave more time for combustion and much improved performance, says Laursen. “With this solution no pilot fuel is needed, potentially leading to a pure ammonia-fuelled engine.”

Another option is to crack a small part of the ammonia into hydrogen and nitrogen and use the hydrogen to ignite the ammonia. “This is however an engine solution that may be some years out in the future. The use of hydrogen in combustion engines requires new construction materials, because of risk of embrittlement, and the design of the injector nozzles/atomizers is especially challenging. Using fuels like LNG, VLSFO and methanol is already making it challenging to source steel materials that are able to withstand the load from both heat and pressure in the combustion chamber.”

Combining propane and ammonia is another option that would be interesting to investigate further, says Laursen, although it may require an emulsifying agent added to the two liquids before they are fully miscible. “LPG carrier owners are today specifying main engines to be able to burn propane and butane. It would be a great benefit for those operators if they could use ammonia as well, mixing 10, 20 or 30% into the LPG to potentially meet GHG regulations over the lifetime of the ship.”

Wärtsilä will have an engine running on ammonia this year. It is unlikely that carbon-neutral ammonia will be available in large quantities initially, and Wärtsilä predicts it will be used as a drop-in fuel while shipowners gain confidence. Wärtsilä’s engine development will follow this anticipated trend, moving from a diesel engine with ammonia capabilities to an engine that is more optimised for ammonia.

Combining LNG and ammonia is another option being explored. Regulations have not yet specified the pressure and temperature at which ammonia needs to be stored onboard a vessel, and Mathias Jansson, Director, Fuel Gas Supply Systems, Wärtsilä Marine Power, says there are strong signals that cryogenic storage will be considered safer when analysing the consequences of a potential leak.

The transition to deploying ammonia as fuel will also have a significant impact on fuel handling on board. For example, if ammonia is used first as a drop-in fuel alongside a dual-fuel LNG vessel configuration, there will need to be three different types of fuel tanks and fuel handling systems onboard: for LNG, diesel and ammonia. Wärtsilä is investigating whether fuel mixing systems are feasible – potentially based on its existing technology for mixing LNG and volatile organic compounds as fuel.

Dominik Schneiter, Vice President of Research and Development at WinGD, says LNG is a good base for converting to ammonia fuel in the future, with LNG-fuelled ships having the tanks, fuel systems and engines suited to conversion. Schneiter says the company is actively investigating ammonia, but notes that there is a wide range of potential new fuels including synthetic diesel, biomass diesel, methanol and ethanol that are suitable for X-DF and X-series WinGD engines.

WinGD has developed test rigs designed specifically to assess the compatibility of any alternative liquid or gaseous fuel with existing fuel systems. The rigs include key elements of the systems, including a variety of fuel pumps, common rail and injection actuation elements as well as the injection valves. An additional investment is a single-cylinder engine that allows for optimisation of both dual-fuel Otto and Diesel engine concepts.

Practical considerations

Schneiter is positive about the viability of combining ammonia with other fuels and the potential for multi-fuel engine development. Ultimately, though, shipowners will be driven by the price of the fuel and the technology, and this may vary regionally, making it unlikely that ammonia will be initially adopted industry-wide. “It’s always a capital – operation – expenditure calculation.”

Emissions are another major development focus for the industry. Ammonia combustion engines carry the potential for ammonia slip, NOx formation and N2O (nitrous oxide) formation. N2O is a particular concern as it is about 285 times more potent as a greenhouse gas than CO2. Another issue is the toxicity of ammonia. Indeed, says Schneiter, some port authorities may expect traditional fuels to be used in port until confidence in ammonia combustion technology grows.

Strategically, WinGD is expanding the scope of its design to include electric power and propulsion solutions. “We have started to look at energy management systems onboard,” says Schneiter. “And we are starting to look at the larger propulsion system, not just the combustion engine, because we see over time that the combustion engine installed power will be reduced in response to IMO regulations. It will still be there, but it will be smaller, a bit more complex, and we can manage this complexity.”

Consequently, a new offering has already been established for electrical system and energy storage integration, and Schneiter envisages it playing a role in meeting emissions regulations, also while vessels are in port. Fuel cells are another technology that WinGD is considering integrating into the electric power system going forward, with ammonia being a promising fuel choice.

MAN Energy Solutions is currently developing the fuel injection system and engine design for its 2-stroke dual-fuel ammonia engine and plans to have a 2-stroke engine available for delivery in 2024 and medium-speed engines ready in 2026. The fuel supply system is based on the LPG supply system for liquid injection, and will use the Liquid Gas Injection (LGI) concept known from the existing dual-fuel LPG injection and tank to engine system. The supply pump will provide the ammonia at low pressure – approximately 80 bar – and a hydraulic booster will be used to reach an actual injection pressure of 500-600 bar. “It is important to note that this is just the pressure when the injection valve opens to the combustion chamber, and only the ammonia injected for that revolution is subjected to that pressure. For reference, a common rail diesel injection in a passenger car has around 1,500 bar. So, this is by no means an untested injection concept,” says Peter Kirkeby, Principal promotion manager, MAN Energy Solutions, Two-stroke.

The engine is being designed for fertiliser grade ammonia, and the piping components will be made from stainless steel (316L). “The use of 316L is made possible by the grade of ammonia chosen – where the industry standard is to have a little bit of water in the ammonia, because that puts you outside the risk of stress corrosion in the pipes as long as you use 316L and the appropriate welding,” says Kirkeby.

A diesel pilot of about 5% will be used when running the engine on ammonia. Kirkeby is confident that the very long stroke of the low-speed engine will enable designers to tune the combustion to ensure emissions are reduced as far as possible. Added to this ability to control emissions is the fully variable exhaust valve timing, injection timing and control of the turbocharging system.

While the engine will have a diesel pilot, Kirkeby foresees that an alternative such as hydrogen could be considered in the longer-term. However, the priority is low given that the amount of pilot fuel required, and which could come from bio or synthetic sources. “Hydrogen is promising in many ways, and it is a very good promoter for combustion, but it increases the complexity of ‘logistics’ in the engineroom.”

MAN aims to make the engine as simple as possible for engineroom crew. “As engineers, our task is to make it simple and reliable and not over-complicated.” MAN is not planning a multi-fuel engine, although its engine portfolio aims to be future proof and can be configured to different fuels. Presently, the company sees no interest from the market that justifies developing a specific engine type that can operate on many different fuel types.

A classification society perspective

DNV is involved in a range of ammonia engine and ship design projects, and Business Development Manager Christos Chryssakis believes that dual-fuel engines will be favoured and does not expect that multi-fuel engines (i.e., engines that can run on both LNG and ammonia) will be deployed as a solution for the industry’s fuel transition. Aside from the complexity, we can reasonably expect that these would be very expensive systems, he says.

Using LNG and LPG as fuel and then later retrofitting the engine to run on ammonia is one combination that could be advantageous, as the same storage tanks could be used for both fuels, if designed specifically for this. Ammonia has a lower energy density though, so this could mean additional tank capacity is required.

Class notations are expected to be published in July, and DNV has already released its Ammonia as a Marine Fuel Safety Handbook. The handbook notes some similarities between LNG and ammonia: both require the management of boil-off gas and protection from external events that could damage storage tanks. Ammonia expands 850 times when going from liquid to gaseous state. This means that one litre of liquid can expand into 170,000 litres of ammonia gas of lethal concentration. Therefore, fuel systems should be designed with a minimum design pressure of 18 bar. This corresponds to the vapour pressure of ammonia at 45oC which is what the International Association of Classification Societies (IACS) specifies as the highest temperature that machinery should be designed to operate at.

DNV is supporting shipowners that are interested in transitioning to ammonia by providing a flexible ammonia-ready notation. Having a fuel tank that can accommodate ammonia or can be retrofitted for this purpose will be one of the qualifiers, as will be having a design that complies with ammonia class rules. Optionally, the notation can also include having the structural strength to accommodate the additional weight of ammonia tanks and fuel, having piping systems, main and auxiliary engines ready and also boilers.

Chryssakis anticipates that many shipowners will wait until after 2030 to take up ammonia, after the engine technology and ship designs have been proven in operation and when green ammonia becomes readily available.

Serge Dal Farra, Global Marketing Director, Lubmarine at TotalEnergies, says the group’s name change to TotalEnergies reflects the energy major’s commitment to investing 50% of its spending on renewables, and this will include green ammonia. The Marine Fuels Division is further developing research into the viability of ammonia as an alternative marine fuel through its participation in a series of leading industry initiatives and Lubmarine is developing the necessary formulation changes to support combustion engines running on ammonia.

Lubmarine is one of just two approved providers of cylinder lubrication products for WinGD’s Dual Fuel engines, through its Talusia Universal platform, which will form the basis for the new ammonia formulation. Nikolaos Kotakis, Technical Director, Lubmarine at TotalEnergies, says properties such as basicity and thermal stability remaining the same. For 4-stroke engines, longevity is something that will have to be monitored, as ammonia could have an impact not seen with fossil fuels. Changing the formulation to boost product lifetime will involve balancing requirements for miscibility and compatibility, and there are technical and commercial parameters to consider. However, he says, monitoring is an important factor in preventative maintenance anyway and something that will be supported by a new generation of onboard testing kits.

Kotakis says the group will be ready when the engines are, although some optimisation may be required after onboard experience is gained. He says that combustion engines are here to stay for at least the next 20 or 30 years, so requirements will change as the new fuel, engine and after-treatment combinations emerge. “We’ll be ready,” he says.