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This paper provides an in-depth analysis of alternative fuels, including liquefied natural gas (LNG), hydrogen, ammonia, and biofuels, assessing their feasibility based on operational requirements, availability, safety concerns, and the infrastructure needed for large-scale adoption. Moreover, it examines hybrid and fully electric propulsion systems, considering advancements in battery technology and the integration of renewable energy sources, such as wind and solar power, to further reduce SOV emissions. Key findings from this research indicate that LNG serves as a viable short- to medium-term solution for reducing GHG emissions in the SOV sector, due to its relatively lower carbon content compared to MDO and HFO. This paper finally insists that while LNG presents an immediate opportunity for emission reduction in the SOV sector, a combination of hydrogen, ammonia, and hybrid propulsion systems will be necessary to meet long-term decarbonisation goals. The findings underscore the importance of coordinated industry efforts, technological innovation, and supportive regulatory frameworks to overcome the technical, economic, and infrastructural challenges associated with decarbonising the maritime industry. [ABSTRACT FROM AUTHOR]

The paper aims to investigate the fuel and system options for a floating power plant (FPP) considering economic performance and the decarbonization goals of the International Maritime Organization. Various case studies have been assessed using a reference FPP, encompassing the instant and future retrofitting scenarios. The ready-to-use scenarios involve alternative fuel and organic Rankine cycle-based waste heat recovery system usage. Nuclear energy systems have been evaluated within the reference FPP since they are suitable candidates for achieving zero-carbon objectives and providing low-cost electricity. A simulation framework created in Python has calculated the fuel consumption regarding the power requirement and organized the approaches used in the study. An environmental model comparing the systems has been built to calculate upstream and operational emissions. The cost projection model for 2030 and 2050 has assessed the economic performance. Technique for Order of Preference by Similarity (TOPSIS) one of the multi-criteria decision-making approaches has ranked the systems considering the outcomes of economic and environmental models over the years. Findings demonstrate that the current fuel usage scenario of the FPP is not suitable both environmentally and economically. The other emissions can be near zero and greenhouse gases can be decreased by up to 15.95% using alternative fuels. Nuclear energy is a strong candidate to meet the 2050 targets, but its viability is largely based on economic performance. [ABSTRACT FROM AUTHOR]

This paper provides an in-depth analysis of alternative fuels, including liquefied natural gas (LNG), hydrogen, ammonia, and biofuels, assessing their feasibility based on operational requirements, availability, safety concerns, and the infrastructure needed for large-scale adoption. Moreover, it examines hybrid and fully electric propulsion systems, considering advancements in battery technology and the integration of renewable energy sources, such as wind and solar power, to further reduce SOV emissions. Key findings from this research indicate that LNG serves as a viable short- to medium-term solution for reducing GHG emissions in the SOV sector, due to its relatively lower carbon content compared to MDO and HFO. This paper finally insists that while LNG presents an immediate opportunity for emission reduction in the SOV sector, a combination of hydrogen, ammonia, and hybrid propulsion systems will be necessary to meet long-term decarbonisation goals. The findings underscore the importance of coordinated industry efforts, technological innovation, and supportive regulatory frameworks to overcome the technical, economic, and infrastructural challenges associated with decarbonising the maritime industry.

This study investigates the transition to a sustainable shipping industry within the framework of the IMO's 2050 carbon neutrality objective, focusing on sociotechnical systems analysis. This research delves into the sustainable paradigm shift towards alternative marine fuels, such as LNG, methanol, ammonia, and hydrogen, from a sociotechnical transition perspective, analyzing the multilevel perspective challenges and opportunities. Specifically, it scrutinizes the implications of adopting these alternative fuels for global shipping, identifying technical uncertainties, financial constraints, and infrastructure needs. Through a comprehensive review of the existing literature on ship emissions and alternative fuels, coupled with sociotechnical transition theory, this study addresses the multifaceted challenges and opportunities in meeting the IMO's environmental objectives. It emphasizes the necessity of collaborative governance, innovative niche strategies, and a holistic approach to leverage the current window of opportunity in facilitating the maritime industry's transition to sustainable fuel options. Finally, this research enhances our understanding of the intricate interplay between technological, social, industrial, and cultural dynamics in the greening of shipping, and offers insights into the strategic adoption of environmentally friendly marine fuels for a sustainable future. [ABSTRACT FROM AUTHOR]

Diverse forms of environmental pollution arise with the introduction of materials or energy that exert adverse effects on human health, climate patterns, ecosystems, and beyond. Rigorous emission regulations for gases resulting from fuel combustion are being enforced by the European Union and the International Maritime Organization (IMO), directed at maritime sectors to mitigate emissions of SOx, NOx, and CO2. The IMO envisions the realisation of its 2050 targets through a suite of strategies encompassing deliberate reductions in vessel speed, enhanced ship operations, improved propulsion systems, and a transition towards low and zero-emission fuels such as LNG, methanol, hydrogen, and ammonia. While the majority of vessels currently depend on heavy fuel or low-sulphur fuel oil, novel designs integrating alternative fuels are gaining prominence. Technologies like exhaust gas purification systems, LNG, and methanol are being embraced to achieve minimised emissions. This study introduces the concept of a high-power combined ship system, composed of a primary main engine, a diesel engine, and a steam turbine system, harnessing the energy contained within the flue gases of the main combustion engine. Assumptions, constraints for calculations, and a thermodynamic evaluation of the combined cycle are outlined. Additionally, the study scrutinises the utilisation of alternative fuels for ship propulsion and their potential to curtail exhaust emissions, with a specific focus on reducing CO2 output.

Diverse forms of environmental pollution arise with the introduction of materials or energy that exert adverse effects on human health, climate patterns, ecosystems, and beyond. Rigorous emission regulations for gases resulting from fuel combustion are being enforced by the European Union and the International Maritime Organization (IMO), directed at maritime sectors to mitigate emissions of SOx, NOx, and CO2. The IMO envisions the realisation of its 2050 targets through a suite of strategies encompassing deliberate reductions in vessel speed, enhanced ship operations, improved propulsion systems, and a transition towards low and zero-emission fuels such as LNG, methanol, hydrogen, and ammonia. While the majority of vessels currently depend on heavy fuel or low-sulphur fuel oil, novel designs integrating alternative fuels are gaining prominence. Technologies like exhaust gas purification systems, LNG, and methanol are being embraced to achieve minimised emissions. This study introduces the concept of a high-power combined ship system, composed of a primary main engine, a diesel engine, and a steam turbine system, harnessing the energy contained within the flue gases of the main combustion engine. Assumptions, constraints for calculations, and a thermodynamic evaluation of the combined cycle are outlined. Additionally, the study scrutinises the utilisation of alternative fuels for ship propulsion and their potential to curtail exhaust emissions, with a specific focus on reducing CO2 output. [ABSTRACT FROM AUTHOR]

Although there are some studies on the impact of Sulphur 2020 on shipping in the literature, large-scale economic analyses are scarce. For this reason, in compliance with sulphur abatement, this study aims to determine the most economical alternatives for shipping companies. First, real data are collected from the maritime industry and scenarios are created regarding different ship types, engine powers, sailing times and fuel prices. In conclusion, using very low sulphur fuel oil alternative for dry cargo ships, hybrid scrubber alternative for crude oil tankers, open-loop scrubber alternative for container ships and hybrid scrubber for Ro-Ro ships are found as economically beneficial in most cases. Last of all, the break-even time from low sulphur fuels to scrubber types is presented to guide shipowners in finding the best alternative with respect to ship ages. [ABSTRACT FROM AUTHOR]

Marine emission policies are becoming more demanding; thus, ship propulsion and power generation technologies need to be adapted to current scenarios. LNG is already considered to be a transition fuel, and new alternative marine fuels are emerging. The aim of this study was to develop an innovative methodology to optimize and adapt the combustion system of an LNG internal combustion marine engine to burn alternative marine fuels. The present study was based on LBG, but the methodology could be replicated with other fuels. A total of six tests were carried out, with three prechamber designs and three spark plug designs. Each test was carried out in a single-cylinder engine with two types of high-methane-number fuel. The influence on thermal efficiency parameters such as the prechamber volume, the orientation of the flame holes, and the existence of a central hole was studied. In the case of the spark plug, the influence of the amount of precious metal in the electrode, its shape and its insertion into the prechamber were analysed. Experiments showed that by modifying both the prechamber and the spark plug, maximum improvements in thermal efficiency of 1.9% can be achieved. Those improvements allowed the LBG engine to suffer only a 4.3% thermal efficiency reduction, as opposed to its LNG counterpart. By applying the proposed methodology, the thermal efficiency of commercially available internal combustion gas engines could be improved. [ABSTRACT FROM AUTHOR]

The Turkish Straits are critical waterways connecting the Mediterranean and the Black Sea. About 38,552 and 43,343 ships pass through the Strait of Istanbul and Strait of Canakkale annually, respectively, and their emissions into the air pose a threat to the regional and global environment, as well as to the people of the region. Herein, the effects of the declaration of the Sea of Marmara as an emission control area and the use of alternative fuels by ships on emission formation were examined. For this purpose, the data of the ships passing through the Turkish Straits were obtained, the engine powers were calculated based on the gross registered tonnage values of these ships, and the emission values were reached. Declaring the Sea of Marmara as an emission control area provides an 80% and 76% reduction in sulfur and nitrogen oxides, respectively. Carbon emissions remained the same. The use of liquefied natural gas dramatically reduces carbon emissions. Alternative fuels, especially liquefied natural gas, effectively reduce sulfur oxide emissions. Despite these positive effects, there seem to be many years ahead of the widespread use of alternative fuels due to the lack of technical and economic infrastructure. Thus, the declaration of the Sea of Marmara as an emission control area will positively affect both the population in the region and the region's environment.

The ambitious targets set by the International Maritime Organization for reducing greenhouse gas emissions from shipping require radical actions by all relevant stakeholders. In this context, the interest in high efficiency and low emissions (even zero in the case of hydrogen) fuel cell technology for maritime applications has been rising during the last decade, pushing the research developed by academia and industries. This paper aims to present a comparative review of the fuel cell systems suitable for the maritime field, focusing on PEMFC and SOFC technologies. This choice is due to the spread of these fuel cell types concerning the other ones in the maritime field. The following issues are analyzed in detail: (i) the main characteristics of fuel cell systems; (ii) the available technology suppliers; (iii) international policies for fuel cells onboard ships; (iv) past and ongoing projects at the international level that aim to assess fuel cell applications in the maritime industry; (v) the possibility to apply fuel cell systems on different ship types. This review aims to be a reference and a guide to state both the limitations and the developing potential of fuel cell systems for different maritime applications. [ABSTRACT FROM AUTHOR]

The main subject of research involves the characteristics and assessment of the already ongoing process of maritime shipping radical decarbonization. There were identified and analyzed international legal and administrative regulatory measures as well as a package of technical, technological, operational and economic solutions, including the possibility of choosing alternative low-emission fuels that are necessary to achieve the already set targets by 2050. This research aimed to indicate and assess the most promising types of measure which are to be applied to achieve the required reduction of CO2 emissions in global shipping as well as developing a potential roadmap leading to their implementation. In the conducted research work, mainly qualitative analyses were applied, i.e., factor analysis (FA), comparative analysis (CA), and a series of consultations with representatives of the maritime industry were carried out, following the procedure typical for the Delphi technique. The main result of the research work is the development of a scenario for potential supply and distribution of fuels to the maritime shipping market by 2050. The basic conclusion is that shortages in manufacturing, commercialization, and supply of low and zero-emission fuels to the shipping market may be the main obstacle hampering the reaching of the targets of shipping industry decarbonization. Such a scenario could significantly slow down the stepping up process of greening the global supply chains. [ABSTRACT FROM AUTHOR]

Alternative marine fuels are considered an important solution for reducing ship emissions from fossil fuels. These fuels have similar energy content with fossil fuels, but they create much less environmental burden during their use due to the elements they contain (or not), the ratio of elements to each other and different combustion characteristics. On the other hand, for these fuels to replace fossil fuels, they must meet a number of important criteria and conditions. These are divided under four main titles: Economic, technical, environmental, social and other. In addition, examining the environmental impacts of alternative fuels from a life-cycle perspective is also important for determining the holistic and cumulative impacts. In this study, the criteria determined for alternative marine fuels were evaluated from the life cycle perspective and it was investigated which criterion is the most important in terms of life cycle. Thus, it is aimed to summarize the assessments of the criteria for acceptance of the alternative fuels. [ABSTRACT FROM AUTHOR]

The Turkish Straits are critical waterways connecting the Mediterranean and the Black Sea. About 38,552 and 43,343 ships pass through the Strait of Istanbul and Strait of Canakkale annually, respectively, and their emissions into the air pose a threat to the regional and global environment, as well as to the people of the region. Herein, the effects of the declaration of the Sea of Marmara as an emission control area and the use of alternative fuels by ships on emission formation were examined. For this purpose, the data of the ships passing through the Turkish Straits were obtained, the engine powers were calculated based on the gross registered tonnage values of these ships, and the emission values were reached. Declaring the Sea of Marmara as an emission control area provides an 80% and 76% reduction in sulfur and nitrogen oxides, respectively. Carbon emissions remained the same. The use of liquefied natural gas dramatically reduces carbon emissions. Alternative fuels, especially liquefied natural gas, effectively reduce sulfur oxide emissions. Despite these positive effects, there seem to be many years ahead of the widespread use of alternative fuels due to the lack of technical and economic infrastructure. Thus, the declaration of the Sea of Marmara as an emission control area will positively affect both the population in the region and the region's environment. [ABSTRACT FROM AUTHOR]

The study investigates marine engineering education on alternative fuels and hybrid propulsion regarding decarbonisation of shipping. A new course is proposed for maritime education and training subject to the IGF Code amendments to the STCW which lasts 14 weeks and 3 h per week. Competences at the STCW amendments for the persons who work on alternative-fuelled ships are taken into account while preparing the course topics. Each topic is paired with basic and advanced training competencies of the STCW amendments, compliance with the STCW is provided, the course topics and sub-topics are explained, and the duration of the course is determined. The need for updating the curriculum and the training of future seafarers is crucial to satisfying their ability to operate future ships. This study highlights the need for novel approaches and courses regarding the new future technologies for the traditional marine engineering curriculum. [ABSTRACT FROM AUTHOR]

The International Maritime Organization (IMO) established new strategies that could lead to a significant reduction in the carbon footprint of the shipping sector to address global warming. A major factor in achieving this goal is transitioning to renewable fuels. This implies a challenge, as not only ship-innovative solutions but also a complete low-carbon fuel supply chain must be implemented. This work provides a method enabling the exploration of the potential of low-carbon fuel technologies for specific shipping routes up to larger sea regions. Several aspects including vessel sizes, impact of weather and shipping routes, emissions savings and costs are considered. The local energy use is determined with proven bottom-up prediction methods based on ship positioning data from the Automatic Identification System (AIS) in combination with weather and ship technical data. This methodology was extended by an approach to the generation of a basic low-carbon fuel system topology that enables the consideration of local demand profiles. The applicability of the proposed approach is discussed at hand via a case study on Roll-on/Roll-off passenger and cargo (RoPax) ferries transitioning from conventional fuels to a compressed hydrogen fuel system. The results indicate a potential reduction in emissions by up to 95% and possible system sizes and costs. [ABSTRACT FROM AUTHOR]

The continuous increase in global maritime freight transport has led to an increase in emissions. The port of Heraklion was selected as a case study to investigate the environmental impact of shipping in wider areas. Two different maritime fuels were examined: the conventional maritime fuel, marine diesel oil (MDO), and an alternative maritime fuel, liquified natural gas (LNG). To carry out this study, real data from the port of Heraklion, the Lloyd's Register Fairplay (LRF) Sea-Web database, and literature reviews were used. The bottom-up method was adopted for data processing. The results of this study demonstrate that alternative maritime fuels, such as LNG, could drastically reduce SO2, NOx, PM, and CO2 emissions. [ABSTRACT FROM AUTHOR]

Marine emission policies are becoming more demanding; thus, ship propulsion and power generation technologies need to be adapted to current scenarios. LNG is already considered to be a transition fuel, and new alternative marine fuels are emerging. The aim of this study was to develop an innovative methodology to optimize and adapt the combustion system of an LNG internal combustion marine engine to burn alternative marine fuels. The present study was based on LBG, but the methodology could be replicated with other fuels. A total of six tests were carried out, with three prechamber designs and three spark plug designs. Each test was carried out in a single-cylinder engine with two types of high-methane-number fuel. The influence on thermal efficiency parameters such as the prechamber volume, the orientation of the flame holes, and the existence of a central hole was studied. In the case of the spark plug, the influence of the amount of precious metal in the electrode, its shape and its insertion into the prechamber were analysed. Experiments showed that by modifying both the prechamber and the spark plug, maximum improvements in thermal efficiency of 1.9% can be achieved. Those improvements allowed the LBG engine to suffer only a 4.3% thermal efficiency reduction, as opposed to its LNG counterpart. By applying the proposed methodology, the thermal efficiency of commercially available internal combustion gas engines could be improved.

The discussion around shipping decarbonization has accelerated rapidly in 2020 and 2021. The growing studies on alternative marine fuels based on different criteria are indicative of both the complexities involved in marine fuels evaluation and absence of a consistent framework for assessment of alternative marine fuels from a holistic perspective. There is a recent call for an integrated evaluation model for alternative marine fuels with respect to economic, environmental, and social criteria. In this study, we develop and present a comprehensive and integrated set of sustainability criteria that are relevant for evaluating alternative marine fuels. First, we provide an overview of different alternative marine fuel pathways and assess the current challenges associated with adopting alternative marine fuels. Second, we develop 18 sustainability criteria, identified through the academic and trade literature and validated through a multi-stakeholder participatory approach (based on the input from 70 maritime experts), for a systematic and consistent evaluation of marine fuels. Third, based on an in-depth survey, we evaluate maritime stakeholder perspectives on the importance of sustainability criteria. And finally, we provide a discussion of key policy implications and areas for future studies. Our analysis reveals the current degree of agreement amongst maritime stakeholders in the debate about the importance of multiple, and often conflicting, criteria for evaluating marine fuels; the top five most important criteria are regulatory compliance, life cycle GHG, fuel cost, air pollution, and occupational health and safety. The analysis also looks at the importance ranking of each criterion from the perspective of individual maritime stakeholder groups. These findings provide decision-makers with a platform to understand priorities and interests of maritime stakeholder groups for the choice of marine fuels.

Various endeavors are undertaken by the maritime industry, academia, and policy-makers to reduce greenhouse gas emissions. These include the search for feasible technologies that could be used onboard merchant vessels and are propelled by international legal and social initiatives. To this end, this study aimed to critically analyze the research trends pertaining to the active methods of reducing the negative environmental impact of shipping. The research is focused on alternative fuels and renewable energy systems with respect to the related policy-making and existing legal framework. Therefore, a bibliometric approach was applied to a sample of 234 scientific papers indexed in the SCI-EXPANDED in Clarivate Analytics Web of Science Core Collection. The results indicate that the scientific efforts were made more on alternative fuels, while renewable energy sources only recently became a popular research subject. Moreover, the environmental benefits of prospective technologies are more investigated than their financial aspects. The research effort on alternative maritime fuels was made in parallel with the legal one, both aiming to combat global climate change and magnifying each other. [ABSTRACT FROM AUTHOR]

• Newly implemented IMO regulations require a significant reduction of ship emissions. • Ship emission studies related to switching to low-sulphur fuels are thoroughly reviewed. • Refinery processes to produce low-sulphur fuels require extra energy consumption. • Scope for new regulations to be added to reduce particle number and methane slip. • Future marine fuel mix needs to be involved to meet fuel regulations and emission reduction. This study presents an overview of the context and global impacts of recent International Maritime Organization (IMO) regulations on the marine fuel oil refining industry, future marine fuel mix and ship emissions. IMO limited marine fuel sulphur content in both Sulphur Emission Control Areas (SECAs) and Nitrogen Oxide Emission Control Areas (NECAs) to 0.1% (wt. %) by 2015, and to 0.5% globally by 2020. It is anticipated that the newly implemented IMO regulations will help to mitigate negative impact of ship emissions on public health and environment. IMO regulations require significant changes to refineries to increase the production of low sulphur fuels through a shift to distillates, use of novel deep desulphurization techniques, or fuel blending. Changes to the refinery processes can bring forth increases in greenhouse gas emissions and high capital investments. Alternative fuels will need to meet the required reduction of air pollutants and greenhouse gas emissions in coastal areas. Alternative marine fuels consisting of liquefied nature gas (LNG) and biofuel may be suitable fuels to meet both targets. These two fuels are predicted to account for 50% of shipping energy demand by 2050, while the remainder will still be supplied by conventional heavy fuel oil (HFO)/marine gas oil (MGO). Switching to low sulphur fuels as a results of the new IMO regulations has led to measureable reductions in ship emissions generally. This fuel switching also resulted in changes in engine emission characteristics, especially on particulate matter chemical composition. [ABSTRACT FROM AUTHOR]

The environmental effects of conventional fossil fuels used in maritime sector is a well-studied subject and various methods, i.e. hull optimization, engine modifications, alternative propulsion systems, and alternative energy sources, have been suggested and implemented for years to reduce these effects. Although the utilization of alternative fuels is accepted as the most effective method, these fuels have their disadvantages as well as advantages they provide. This study mainly aims to evaluate the alternatives (ammonia, biofuels, dimethyl ether, ethanol, hydrogen, liquefied natural gas, liquefied petroleum gas, and methanol) through a comprehensive literature review. For this purpose, the publications obtained from Web of Science were searched using the keyword alternative marine fuels and the studies accessed were evaluated. In this context, the study is one of the most comprehensive reviews on alternative marine fuels and aims to discuss the future of alternative fuels through the evaluation of existing studies. The properties of these fuels have been examined in detail, taking care not to miss any point. Driving forces and obstacles for alternative fuels to be called conventional fuels have been evaluated in line with the United Nations' Sustainable Development Goals. In light of the gathered information, it has been concluded that the global-scale use of alternative fuels is still at an early stage due to several major concerns, i.e. technical and environmental incompatibilities, cost issues, and insufficient training level of seafarers, and that future studies should be carried out, especially within the life cycle perspective. • A comprehensive review on comparing alternative fuels. • Assessment of calling alternatives as conventional in accordance with LCA and SDGs. • No alternative fuel is yet able to provide sufficient and necessary conditions. • Future assessments should be conducted with a focus on LCA. [ABSTRACT FROM AUTHOR]

Increasing amount of shipboard emissions, and emission regulations entered into force encourage emission reduction technologies to be developed, and new methods to be used. Alternative fuel use as a fuel on marine diesel engines is one of the new methods to reduce shipboard emissions. Methanol and ethanol can be used as a liquid fuel or liquefied natural gas and hydrogen can be used as a gaseous fuel on ships. Aim of this study is to make scientific comparison of alternative fuels which can be used at ships. The environmental and economical performance of methanol, ethanol, liquefied natural gas, and hydrogen were compared. Comparison was made by eleven comparison criterions from different aspects. The most suitable alternative fuel which can be used on ships is determined by defining evaluation scale points for each comparison criterions. Analytic hierarchy process was used to find the weighing of comparison criterions according to given points by five experts to each criterions. Final comparison table is formed including all comparison criterions with given evaluation scale points of each alternative fuels, and weighing for each criterion depend on their importance at maritime sector. Methanol and ethanol, liquefied natural gas, and hydrogen get comparison points of 2.129, 4.092 and 3.796 respectively from the total point of 5.005. Comparison shows that methanol and ethanol do not seem to be preferable to use onboard due to their inadequacy which are investigated in the study. Liquefied natural gas gets the highest total evaluation point in the study, and the most suitable alternative fuel. Hydrogen gets the highest point at safety, bunker capability, durability, adaptability to existing ships, and commercial effects criterions. This study shows that hydrogen can be the alternative to liquefied natural gas used as a fuel at ships, but it requires more studies and improvement on the comply with emission regulations and effect on engine components issues. [ABSTRACT FROM AUTHOR]

Due to the growing concerns of emissions from the shipping industry, the International Maritime Organization (IMO) has set strategies to reduce the CO 2 intensity by 40% in 2030 and cut total GHGs emissions by at least 50% by 2050, with 2008 as a baseline. Clean alternative marine fuels are widely recognized and used as a viable solution for reducing ship-related air pollution. Several studies including traditional reviews have been conducted to examine the literature on cleaner alternative marine fuels and their role in decarbonizing the shipping sector. However, these studies fail to unpack the main research actors, evolutionary nuances, and emerging research hotspots in this field. To quantitatively and qualitatively explore this research field, the current study adopts a bibliometric analysis. 583 eligible documents published from 2000 to 2020 were retrieved and merged from the Web of Science Core Collection and Scopus databases, and analyzed with the R-studio bibliometrix package (Biblioshiny). Results revealed that the field is growing significantly at a growth rate of 15.8%, with key contributions to the field originating from the USA. Liquified Natural Gas has been identified as the most researched alternative shipping fuel. However, recent trends show researchers turning their attention towards methanol, ammonia, and hydrogen fuels. By analyzing the frequently used keywords and relevant articles, it became clear that the research community has focused mainly on the potential of different alternative fuels as a replacement to conventional marine fuels to limit the emissions from the shipping sector from an environmental, technical, and economic perspective. The current study offers a basis for future research into the decarbonization of the shipping industry. [Display omitted] • Bibliometric study on clean marine fuels based on Web of Science and Scopus databases. • A growing research field with an annual growth rate of 15.8%. • Key authors, institutions and countries in the field have been identified. • LNG emerged as the most researched alternative shipping fuel. • Research hotspots and trends on clean marine fuels discussed. [ABSTRACT FROM AUTHOR]

Within the context of achieving low carbon shipping by 2050, high hopes are placed on alternative marine fuels in addition to a large number of technological and operational measures. A technological review has been carried out in this paper to determine the most promising alternative marine fuels considering the simultaneous reduction of sulphur oxides, nitrogen oxides and carbon dioxide emissions as well as sustainability. Firstly, potential alternative marine fuel options have been summarized based on a review of published literature. Then, key physicochemical properties, feedstocks, production processes, transportation and storage factors, and end uses of zero carbon or carbon-neutral fuels have been analyzed. Finally, a qualitative ranking of the potential of different marine fuel options is presented based on a multi-dimensional decision-making framework. It was found that zero carbon synthetic fuels including hydrogen and ammonia accompanied by clean production could play a vital role in domestic and short sea shipping, though current costs and infrastructure are not commercially feasible. Methanol (fossil/renewable) appears likely to be the most promising alternative fuel for global shipping instead of other carbon-neutral biofuels such as renewable natural gas, bioethanol, biogenic dimethyl ether and biodiesels, which may be feasible for domestic and short sea shipping depending on local practices. It should be highlighted that marine fuel substitution is a prolonged process. Accordingly, consensus-building and action-adopting in the maritime community as early as possible is important to anchor expectations and achieve the goals of clean maritime transportation. • Renewable methanol appears to be the most promising fuel option for global shipping. • Potential of hydrogen and ammonia is mainly in domestic and short sea shipping. • Prospects of alternative marine fuels significantly depend on the world energy mix. [ABSTRACT FROM AUTHOR]

Fuel cells as clean power sources are very attractive for the maritime sector, which is committed to sustainability and reducing greenhouse gas and atmospheric pollutant emissions from ships. This paper presents a technological review on fuel cell power systems for maritime applications from the past two decades. The available fuels including hydrogen, ammonia, renewable methane and methanol for fuel cells under the context of sustainable maritime transportation and their pre-processing technologies are analyzed. Proton exchange membrane, molten carbonate and solid oxide fuel cells are found to be the most promising options for maritime applications, once energy efficiency, power capacity and sensitivity to fuel impurities are considered. The types, layouts and characteristics of fuel cell modules are summarized based on the existing applications in particular industrial or residential sectors. The various research and demonstration projects of fuel cell power systems in the maritime industry are reviewed and the challenges with regard to power capacity, safety, reliability, durability, operability and costs are analyzed. Currently, power capacity, costs and lifetime of the fuel cell stack are the primary barriers. Coupling with batteries, modularization, mass production and optimized operating and control strategies are all important pathways to improve the performance of fuel cell power systems. [ABSTRACT FROM AUTHOR]