According to the latest Alternative Fuels Insight report from DNV, not a single ammonia-powered vessel has been ordered to date — although it expects the first orders soon.

The technology, however, is not quite there yet, with the first ammonia engines still being developed.

For instance, MAN Energy Solutions aims to have a commercially available two-stroke dual-fuel ammonia engine for large ocean-going vessels in 2024, while Finnish supplier Wärtsilä plans to retrofit its first two-stroke ammonia engine into a vessel by 2025 — after securing €10m in funding from the European Commission.

Japanese shipping company Mitsui OSK Lines signed a memorandum of understanding with MAN in 2021 to purchase ammonia engines from the German company, but there was no deadline on the arrangement.

“Ammonia has generated a lot of interest, especially from the deep-sea ship segments, and it has a lot of potential — but developing an engine that is powered by ammonia has been a challenge,” Peter Kirkeby, principal specialist on dual-fuel engines at MAN, was quoted as saying in a DNV report published in February.

“One of the biggest hurdles is how to burn ammonia efficiently to extract the maximum amount of power while making sure the engine is still a compact design.”

By nature, NH3 burns much more slowly than diesel oil, and needs a higher temperature to start “autoignition”. This means that sustaining combustion is harder than with other fuels.

“And, of course, you also need to ensure that the engine allows for the usual performance peaks that come with acceleration, etc,” added Kirkeby. “We are planning for a final fuel mix that would contain around 95% ammonia and 5% of a pilot fuel such as marine gas oil. In the future this could even be biofuel.”

In the short term at least, ammonia seems to be losing out in the alternative-fuels shipping market.

DNV says that 54 methanol-powered ships are currently in service or have been ordered, compared to eight hydrogen vessels and zero ammonia ones.

Methanol (CH3OH) has an even higher volumetric density than ammonia — 4.33kWh per litre, compared to 3.5 — and it is also far easier to handle, being a liquid at room temperature under atmospheric pressure. However, methanol does contain carbon, and to be “carbon-neutral” would require a biogenic source of CO2 for carbon capture, green hydrogen as its base chemical, as well as renewable energy to power the energy-intensive manufacturing process.

According to Recharge’s sister newspaper, TradeWinds, three big-name shipowners — Denmark’s Maersk, Germany’s MPCC and France’s CMA CGM — have already ordered 26 methanol dual-fuel vessels between them. And three more major operators — Cosco, Eastern Pacific and Pacific International Lines — are eyeing methanol propulsion for their next round of new container ships.

Dual-fuel engines that can run on both methanol and traditional fossil fuel are the favoured option at present because methanol is not yet available as a shipping fuel at any kind of scale.

“Owners are waking up to the fact that the next alternative — ammonia — is not that easy,” one ship broker told TradeWinds, pointing to ammonia’s toxicity and the need to remove nitrous oxide — a potent greenhouse gas produced when burning ammonia — from the exhaust stream.

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