Safety, Decarbonization, and the Combustion of Alternative Fuel: MAN Energy’s AmmoniaMot 2

MAN Energy Solutions recently announced a significant development for its marine-based ammonia engine work: the AmmoniaMot 2 research project. With funding from the German government and extensive industry partnerships, the project’s aim is to develop a four-stroke, medium-speed, dual-fuel test engine that operates on ammonia for large-scale ship applications. This follows the design and testing of its first two-stroke ammonia engine.

Christian Kunkel, Head of Combustion Development and Four-Stroke R&D at MAN Energy, provided more details on the ammonia project, including takeaways from the original AmmoniaMot, the advantages of ammonia as a marine fuel, its inherent toxicity challenges, and additional work to decarbonize the maritime industry.

TURBO: How will the successful design and testing of a two-stroke ammonia model assist the development of a four-stroke engine? What were the takeaways from the initial AmmoniaMot project?

Kunkel: An advantage for AmmoniaMot 2 is to have the two-stroke engine development in parallel to the project. Of course, we are using synergies between two-stroke and four-stroke in both directions with a deep technological exchange. As far as ammonia is concerned, we can copy and adapt some of the technical concepts and ideas from two-stroke engine development, mainly in the fields of safety concepts, compatibility of materials, and lube oil.

In the first AmmoniaMot project, we focused on fundamental investigations regarding the combustion of ammonia in an internal combustion engine. The main takeaways from the AmmoniaMot project [that apply to developing four-stroke engines] were:

• ammonia seems to be a suitable fuel to operate four-stroke medium-speed engines
• a greenhouse gas (GHG) reduction potential of up to 90%
• usual exhaust-gas after-treatment systems can be used to fulfill the IMO Tier 3 emission limits

Four-stroke marine engine; image credit: MAN Energy Solutions

TURBO: What are the challenges of integrating ammonia into internal combustion engines for marine applications?

Kunkel: The challenges lie primarily in the area of safety. Ammonia is a toxic substance and leaks must be avoided, which makes developing elaborated safety concepts challenging. In this area, we are profiting from the knowledge and experience of our two-stroke colleagues that already progressed in developing and successfully testing such safety concepts.

Additionally, suitable injection systems must be developed and validated. At first sight, ammonia’s combustion properties were not ideal, but after testing ammonia combustion in different engine types, we are comfortable handling ammonia as an engine fuel. From what we know now, laughing gas emissions may not be the challenge. Thus, advanced selective catalytic reduction systems are sufficient—only minor adaptions are necessary.

TURBO: Besides reduced GHG emissions, what are the advantages of using ammonia as an alternative fuel in the maritime industry? What are the drawbacks or risks?

Kunkel: Ammonia has numerous advantages. To name a few: the production process of ammonia (Haber-Bosch process) is well-known and technically mastered on a large industrial scale. Instead of CO₂, as for other carbon-based e-fuels, N₂ (~80% in the air) is used in the production process. As ammonia is one of the most widely produced chemicals, transportation and handling are also proven and its handling costs are comparably cheap, especially when compared to hydrogen. For example, to keep hydrogen in its liquid form, you need to cool it down to -253° C; however, ammonia only requires -33° C, which makes it easier to store.

Furthermore, ammonia can be produced both as green ammonia (feedstock hydrogen produced by green power and electrolysis) and blue ammonia (feedstock hydrogen based on natural gas and carbon capture and storage). In the long run, only green ammonia makes sense and needs to be achieved, but blue ammonia could bridge the gap until enough green electricity and green hydrogen are available for green ammonia production. This means that ammonia production can already be quickly ramped up.

TURBO: What makes ammonia more suited for vessels without passengers while methanol is better suited for ferries and cruise liners?

Kunkel: Due to its toxicity, safety concepts for ammonia are more challenging than methanol. For example, methanol dilutes very quickly in water and no severe damage is done to nature and the environment. The on-board safety measures with methanol are significantly easier to fulfill compared to ammonia. This makes methanol especially suitable for cruise ships and ferries, which are basically floating cities.

Ammonia is specifically suitable for new-build ships in applications with limited crew sizes where the focus is on fuel price and compromises concerning tank geometry and installation are easier to fulfill.

TURBO: How else is MAN Energy Solutions working to decarbonize marine propulsion?

Kunkel: We’re engaged in many activities to decarbonize marine propulsion. For example, we also offer components and products for the production of climate-neutral fuels that are required for decarbonization. We have compressors needed for transportation via pipeline, and we develop and produce electrolyzers (via our subsidiary Quest One, formerly H-TEC SYSTEMS) to produce green hydrogen. We also offer full-scale methanation plants for the production of carbon-neutral synthetic methane. All our dual-fuel and gas engines can run on synthetic methane, and we have developed technologies to reduce methane slip in these engines.