The shipping industry, responsible for nearly 3% of annual carbon dioxide emissions, is seeking sustainable fuel options to reduce its environmental impact. The International Maritime Organization (IMO) has set an ambitious target of cutting emissions by 50% from 2008 levels by 2050. Among the alternatives being explored, ammonia has emerged as a potential game-changer. However, experts caution that its widespread adoption may introduce new environmental and technical challenges.
The Appeal of Ammonia as a Marine Fuel
Ammonia is abundant and can be produced using renewable energy sources like wind and solar power. As a globally manufactured and traded commodity—primarily for fertilizers—it offers scalability. Its carbon-free combustion and low cost make it an attractive option for the maritime sector.
Earlier this year, Singapore witnessed the world’s first use of ammonia in a dual-fueled vessel, marking a milestone in sustainable shipping. Major companies such as Yara and Maersk have already invested billions of dollars in developing its fueled ships, signaling growing confidence in its potential.
Environmental and Technical Challenges
Despite its promise, ammonia is not without flaws. “Although ammonia is carbon-free, its combustion in engines is not free from greenhouse gas emissions,” explains Selma Brynolf, a researcher at Chalmers University of Technology. Engine tests have revealed emissions of nitrous oxide, a potent greenhouse gas with over 200 times the global warming potential of carbon dioxide.
Other environmental impacts include ammonia’s toxicity to humans, significant resource demands for its production (minerals, metals, and water), and safety concerns related to storage and handling.
According to Claus W. Graugaard, CTO at the Maersk Mc-Kinney Møller Centre for Zero Carbon Shipping, “To unlock the potential of sustainable ammonia as an alternative marine fuel, we must carefully address onboard safety and ensure a safe working environment for seafarers and port workers.”
Efficiency and Design Limitations
Ammonia has a lower energy density and volumetric efficiency than diesel. Ships powered by ammonia engines require larger storage tanks, which add weight and reduce operating range. These factors make ammonia more suitable for deep-sea cargo vessels, where storage capacity is less of a constraint, than for short-sea, passenger, or inland waterway ships.
Moreover, the complexity of handling ammonia’s toxicity adds another layer of challenge to ship design and operation. Compared to conventional or other low-flashpoint fuels, ammonia-powered vessels may require more advanced safety systems, potentially limiting their application.
“Even though green ammonia is a fossil-free and relatively clean fuel, it is probably not green enough for the environment as a whole. More risk assessments on the emissions of ammonia, and the related nitrogen compounds, need to be done before adopting this fuel for shipping,” says Fayas Malik Kanchiralla, PhD student at the Department of Mechanics and Maritime Sciences at Chalmers.
