Decarbonization of Maritime Engines with Alternative Fuels: Impact of Biofuels on Autonomy and Economicity

The maritime sector faces increasing pressure to decarbonize, following the International Maritime Organization’s (IMO) 2023 GHG Strategy, which mandates net-zero emissions from international shipping by 2050 and sets ambitious interim reduction targets. In alignment with these goals, this study investigates the technical, economic, and environmental feasibility of four alternative fuel routes for marine diesel engines, emphasizing blends of biofuels and low-carbon energy carriers. Route 1 explores ethanol–biodiesel (fatty acids methyl esters or FAME)–diesel ternary blends stabilized with an additive; Route 2 examines additized ethanol enhanced for use in compression ignition engines; Route 3 evaluates ammonia in a dual fuel approach; and Route 4 considers combinations of ethanol and FAME with Very Low Sulfur Fuel Oil (VLSFO). Each route is assessed in terms of blend cost, required fuel volume, and carbon intensity (CI), as well as the minimum premium necessary to match fossil fuel prices, based on lower heating value (LHV) and historical market data. Results indicate that Route 2 presents the lowest cost and highest economic viability, though technical barriers remain due to the low flashpoint and lubricity concerns. Route 3 offers the greatest potential for CI reduction, reaching up to 100% with green ammonia, but remains limited by inflated costs and low technical maturity. Routes 1 and 4 offer moderate environmental benefits but require targeted incentives to offset their price gaps. All routes suffer from reduced LHV compared to fossil fuels, necessitating higher fuel volumes to deliver equivalent energy. The findings underscore the critical role of policy intervention in supporting the scale-up of alternative marine fuels, including the adoption of carbon pricing Recommendations include investment in fuel infrastructure, regulatory updates, and support for R&D. These measures are essential to accelerate the maritime energy transition while ensuring environmental integrity and economic feasibility.