The 190 metre ships are equipped with HHI’s high-pressure ammonia direct injection engine – known as the HiMSEN Ammonia Dual Fuel Engine – which secured class approvals in 2024.

The two ships, named Antwerpen and Arlon, are the first in a production run of four commissioned for Exmar LPG France in 2023 and 2024. They are set to be delivered to the shipowner in May and July, respectively.

HHI’s propulsion system compresses air in its combustion chamber, then burns it by injecting ammonia at high pressures. The combustion is ignited using conventional marine fuel.

Under dual fuel operation, marine engines target up to 90-95% of the energy coming from ammonia. The HiMSEN also has a fallback capacity for running entirely on standard marine fuels.

HHI says it has been contracted for a total of eight ammonia-powered vessels.

Globally, maritime players face pressure to offer clean fuel solutions for decarbonisation in line with the International Maritime Organization net-zero framework and regional mandates like the FuelEU Maritime regulation.

Ammonia, which is considered key for progressing the sector, offers zero carbon emissions at use, easier storage than hydrogen, and compatibility with existing global infrastructure and emerging marine engine technologies.

However, while it removes carbon emissions, it is criticised for challenges around its combustion efficiency, toxicity, and production of nitrogen oxides. While also a widely traded commodity, the vast majority of ammonia is produced using unabated fossil fuels.