HiMSEN's new low-pressure ammonia four-stroke engine marks testing milestone

A new low-pressure, four-stroke ammonia dual-fuel marine engine based on the Otto cycle developed by HD Hyundai Heavy Industries Engine & Machinery (HHI-EMD) has completed the Type Approval Test (TAT) process, marking an important step towards commercialisation.

Seven major class societies supported the successful completion of the TAT for HHI-EMD’s HiMSEN H22CDF-GA low-pressure gas ammonia dual-fuel engine. The tests were conducted by HD Hyundai Heavy Industries Engine & Machinery (HHI-EMD) from October 27 to 29 at the Korean Register Green Ship Equipment Test & Certification Center (KR TCC) in Gunsan, South Korea. Classification societies Korean Register, ABS, Bureau Veritas, DNV, ClassNK, Lloyd’s Register, and RINA witnessed the testing. Type approval is essential for marine equipment, ensuring that its design complies with class requirements for safety and international regulatory compliance.

An excellent hydrogen carrier that emits no carbon when combusted, ammonia is seen by some shipowners as a promising alternative fuel to decarbonise shipping. Several ammonia dual-fuelled gas carriers and bulk carriers equipped with two-stroke engine technology have entered service in 2026.

The newly type-approved H22CDF-GA is part of HHI-EMD’s expanding portfolio of four-stroke ammonia dual-fuel engines based on the Diesel and Otto cycles. The company completed TATs for the H22CDF-LA in 2024 and the H32CDF-LA in 2025, both with a high-pressure liquid ammonia fuel supply system based on the Diesel-cycle concept.
By contrast, the H22CDF-GA has a low-pressure gaseous ammonia fuel supply system, simplifying the fuel supply system while lowering capex for shipowners.
The testing also marks the first time a HiMSEN engine TAT was conducted at KR TCC, Korean Register’s specialised test and certification facility, through technical cooperation between HHI-EMD and KR. The two parties plan to further strengthen their technical cooperation in the development of alternative-fuelled engines.