A review of alternative liquid fuels in marine engines

• Maritime sustainability demands a shift to alternative fuels like LNG, ammonia, and hydrogen. • A SWOT analysis reveals major trade-offs in emissions, cost, and operational feasibility. • Dual-fuel technology is a crucial pathway but faces spray combustion optimisation challenges. • Since 2017, research output has surged, mirroring intensified decarbonisation efforts. • A holistic approach is essential to overcome technological, economic, and safety barriers. Given the maritime sector’s vital role in global trade and its substantial environmental impact, the transition to sustainable liquid fuels is a critical imperative. This review provides a holistic analysis, specifically examining the interplay between environmental regulations and the unique operational requirements of marine engines. A range of alternative fuels, including LNG, biofuels, methanol, hydrogen, and ammonia, is evaluated in this study. Each fuel’s viability is critically assessed through a detailed strengths, weaknesses, opportunities, and threats analysis, alongside an in-depth discussion of the significant technical and safety challenges hindering their adoption, such as ammonia’s toxicity, hydrogen storage requirements, and LNG’s methane slip. The review also explores the complex spray combustion dynamics essential for integrating these fuels into marine internal combustion engines, highlighting how fundamental phenomena directly impact the design and performance in this specific context. By uniquely combining technical, safety, and strategic insights, this paper offers a focused and highly relevant resource for stakeholders navigating the sustainable maritime future.