Carbon-free fuel under development for two-stroke engines; key challenges are toxicity, NOx, and ammonia slip.
In practice
Ammonia adoption is in pilot phase 2026-2028. Toxicity is the dominant hazard; vessel-specific risk assessment under IGF Code interim guidelines is required.
Regulatory detail & full definition
Carbon-free fuel under development for two-stroke and four-stroke marine engines. Ammonia (NH3) burns without producing CO2 but generates NOx and unburned ammonia (slip), both of which require post-treatment. IMO MSC.1/Circ.1654 publishes interim guidelines for safety of ships using ammonia as fuel, addressing toxicity, leak detection, ventilation, and personal-protective requirements. First commercial-scale ammonia-fuelled vessels are entering service in 2026–2027, principally in deep-sea bulker, tanker, and PCTC trades. Production from renewable hydrogen is the climate-neutral pathway; current ammonia is principally produced from natural gas.