Alternative Maritime Fuels for Net-Zero Shipping: A Comprehensive Operational, Techno-Economic and Regulatory Review

The maritime shipping industry faces the challenge of decarbonising its operations while maintaining economic viability. We present a comprehensive techno-economic review of four alternative energy carriers, liquid hydrogen (LH2), ammonia (NH3), liquefied natural gas (LNG), and methanol, evaluating their suitability for maritime applications within the context of global decarbonisation policy. Through the comparative assessment of physicochemical properties, hazard profiles, storage requirements, and regulatory compliance mechanisms, this review demonstrates that fuel selection is highly route-dependent, with methanol emerging as the most practical near-term solution for short-sea corridors, ammonia emerging as the primary pathway for long-term deep-sea decarbonisation, leveraging existing production infrastructure to achieve up to 90% lifecycle GHG reduction when produced from renewable hydrogen, and hydrogen serving as an alternative option pending cryogenic infrastructure maturation. The integration of digital twin technologies and port call optimisation provides a realistic pathway to achieving International Maritime Organisation (IMO) decarbonisation targets by 2030 and beyond. The findings are contextualised within current and emerging regulatory frameworks, including MARPOL Annex VI and FuelEU Maritime, to support evidence-based fuel selection and infrastructure investment decisions.