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.

Methanol as marine fuel represents one of the most cost-effective and practical solutions towards low-carbon shipping. Methanol fueled internal combustion engines have a high level of technological readiness and are already available on the market; however, technical data in terms of fuel consumption and emissions are not yet easily accessible. For this reason, the present study deals with the simulation of a virtual spark-ignition methanol engine, carried out in a Matlab-Simulink^© R2023a environment to assess the CO₂ emissions in several working conditions of a possible ship power system. The thermodynamic model of the methanol fueled engine is derived from a marine gas engine simulator, already validated by the authors in a previous work. This article presents the relevant modifications necessary to adapt the engine to the methanol fuel mode with regard to the different fuel characteristics. The simulation analysis compares the results of the virtual methanol engine with available data from a similar, existing gas engine, highlighting the differences in efficiency and carbon dioxide emissions.

The interest in analyzing alternative fuels and new propulsion technologies for shipping decarbonization is growing rapidly. This paper aims to evaluate the performance of high-temperature polymeric exchange membrane fuel cells (HT-PEMFCs) fed by reformed methanol and their potential application as a propulsion system for vessels. The proposed system is intended to be installed on board a 10 m long ship, designed for commercial use in the marine area of Capri Island. Numerical and experimental analyses were performed to estimate the system’s performance, and a feasibility assessment was carried out to verify its real applicability on board the reference case study. From the numerical perspective, a CFD model of the ship hull, as well as a thermochemical model of the propulsion system, was developed. From the experimental point of view, the system behavior was tested by means of a dedicated test bench. The results of the numerical models allowed for the sizing of the propulsion system and the calculation of the fuel consumption. In particular, to satisfy the ship’s power demand, two 5 kW HT-PEMFCs were needed, with a total fuel consumption of 12.7 kg over a typical daily cruise, with a methanol consumption of 1.88 kg/h during cruising at 7 knots. The feasibility analysis highlighted that the propulsion system fits the vessel’s requirements, both in terms of volume and weight.

The study presents a comprehensive comparison among traditional marine fossil fuels and seven alternative unconventional solutions: fossil-based fuels (natural gas (NG) and methanol), biological (HVO, bio-NG, and bio-methanol), and synthetic fuels (NG and methanol). The comparison evaluates technical, economic, and environmental aspects. The case study focuses on the mechanical propulsion system performance of a small luxury passenger ship, simulated by using a mathematical model developed in a Matlab-Simulink environment. In the simulation, the ship's original engines have been replaced with alternative engines of comparable power and RPM, which are compatible with the fuels under consideration. In addition to GHG evaluation, the study uses International Maritime Organization parameters such as the EEXI and the CII to assess the environmental impact of fuels. From an economic perspective, the vessel’s propulsion system has been evaluated based on CAPEX and OPEX indices, providing a holistic view of the feasibility and sustainability of each fuel option.

High-Temperature Proton Exchange Membrane (HT-PEM) fuel cells are promising systems for sustainable maritime transportation and offer significant environmental and operational benefits by utilizing methanol as a clean fuel. While during steady-state operations HT-PEMs produce negligible amounts of pollutants, during transient operational phases, and in particular during start-up, these systems can lead to the formation of additional pollutants. This work reports preliminary results on the development of an Exhaust Gas Cleaning System (EGCS) specifically designed for integration with HT-PEM systems. The EGCS utilizes a fixed-bed adsorption process, chosen for its adaptability to variable pollutant loads and effectiveness on low pollutant concentrations and is based on a literature study and a model. The unit is capable of operating on demand, with a backpressure below 2 mbar and a negligible fuel penalty. The study demonstrates the effectiveness of an integrated approach to emission mitigation and supports the broader transition towards sustainable and environmentally responsible maritime propulsion technologies.