Comparative analysis among different alternative fuels for ship propulsion in a well-to-wake perspective

The shipping sector is required to give a significant contribution to the reduction of Green House Gas (GHG) emissions, according to the ambitious goals fixed by the International Maritime Organization (IMO). To achieve these targets, new technologies and measures are required, related to logistics, digitalization, hydrodynamics, machinery, energy, and aftertreatment. A large potential to reduce GHG emissions is offered by alternative fuels. In this perspective a Well-to-Wake (WtW) approach is due for a comprehensive analysis. The paper is focused on the evaluation of WtW CO2 equivalent emission factors for LNG, methanol, and ammonia. The extensive bibliographic research on this topic outlines the large differences occurring when considering grey or green fuel production pathways. A case study based on a cruise ship allows to compare alternative fuels produced from fossil or renewable sources, considering two typical cruise profiles. Results in terms of Carbon Intensity Indicator confirms that the WtW approach points out the great potential of alternative green fuels for GHG emissions reduction. •Alternative fuels (LNG, ammonia, methanol) for ship propulsion are compared.•A Well-to-Wake approach is applied to evaluate green-house gas emission factors.•Grey and green options for the alternative fuels are considered.•A cruise ship is selected as a case study, with two different cruise profiles.•A simulated Carbon Intensity Indicator (CII) is calculated, to assess GHG emissions reduction on an operational base.