The Maritime Sector and Its Problematic Decarbonization: A Systematic Review of the Contribution of Alternative Fuels
Abstract
This Research was funded by the Science and Technology Foundation (FCT), Ministry of Science and Higher Education (MCTES), European Social Fund (FSE), and Europe Union (EU), under the grant number PD/BD/142848/2018.
Full text
Citation: dos Santos, V.A.; Pereira da Silva, P.; Serrano, L.M.V. The Maritime Sector and Its Problematic Decarbonization: A Systematic Review of the Contribution of Alternative Fuels. Energies 2022,15, 3571. https://doi.org/10.3390/ en15103571 Academic Editors: Eugenio Meloni, Alberto-Jesus Perea-Moreno, José Carlos Magalhães Pires, Juri Belikov, Iva Ridjan Skov, Giorgio Vilardi and Antonio Zuorro Received: 4 April 2022 Accepted: 5 May 2022 Published: 13 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Review The Maritime Sector and Its Problematic Decarbonization: A Systematic Review of the Contribution of Alternative Fuels Vinicius Andrade dos Santos 1,2 , Patrícia Pereira da Silva 1,3,4,5,* and Luís Manuel Ventura Serrano 6,7,* 1 MIT-Portugal Programme, Energy for Sustainability Initiative (EFS), Department of Mechanical Engineering, University of Coimbra, 3030-194 Coimbra, Portugal; [email protected] 2Chemical Process Engineering and Forest Products Research Centre (CIEPQPF), Chemical Engineering Department, University of Coimbra, 3030-790 Coimbra, Portugal 3Centre for Business and Economic Research (CeBER), University of Coimbra, Av Dias da Silva, 165, 3004-512 Coimbra, Portugal 4Faculty of Economics, University of Coimbra, Av Dias da Silva, 165, 3004-512 Coimbra, Portugal 5The Institute for Systems Engineering and Computers at Coimbra INESC, University of Coimbra, Pólo II, 3030-290 Coimbra, Portugal 6School of Technology and Management, Polytechnic of Leiria, 2411-901 Leiria, Portugal 7Association for Development of Industrial Aerodynamics (ADAI), University of Coimbra, 3030-788 Coimbra, Portugal *Correspondence: [email protected] (P.P.d.S.); [email protected] (L.M.V.S.) Abstract: The present study seeks to select the most important articles and reviews from the Web of Science database that approached alternative fuels towards the decarbonization of the maritime sector. Through a systematic review methodology, a combination of keywords and manual refining found a contribution of 103 works worldwide, the European continent accounting for 57% of all publications. Twenty-two types of fuels were cited by the authors, liquefied natural gas (LNG), hydrogen, and biodiesel contributing to 49% of the mentions. Greenhouse gases, sulfur oxide, nitrogen oxide, and particulate matter reductions are some of the main advantages of cleaner sources if used by the vessels. Nevertheless, there is a lack of practical research on new standards, engine performance, cost, and regulations from the academy to direct more stakeholders towards low carbon intensity in the shipping sector. Keywords: low carbon fuels; greenhouse gases; maritime transportation; systematic review 1. Introduction In past centuries the maritime sector has proved to be the most important means of transport of world goods, transporting more than 1 billion tons of products by sea worldwide, growing at an average rate of 3% per year since 1970 [ 1 ]. Although sea transportation is the best indicator of the world economic growth, the side effect has been the impact regarding the complexity of decarbonization measures. Nowadays, maritime fossil fuel consumption accounts for around 2.2 million barrels of oil equivalent (MBOE), which represents almost 1000 million tons of equivalent carbon dioxide (MtCO 2 eq), reflecting 3% of global emissions [ 2 ]. Moreover, the so-called bunker fuel has a very low quality, impacting high emissions of sulfur oxide (SOx), nitrogen oxide (NOx), and particulate matter (PM) [3,4]. The Sulfur Emission Control Areas (SECA) entered into force in 2015 to reduce the sulfur content from 4.5% to 0.1% in the Baltic Sea and American coast and 0.5% elsewhere in 2020. The NOx emission reduction regulations have also been in place since 2016 [5]. The demand for low emissions for such compounds triggered a trend toward cleaner fuels, as well as the concerns over the greenhouse gases (GHG) emission reductions, which have drawn the attention of governments worldwide. Energies 2022,15, 3571. https://doi.org/10.3390/en15103571 https://www.mdpi.com/journal/energies
Energies 2022,15, 3571 2 of 30 Since 2011, the International Maritime Organization (IMO) has implemented a regulatory measure of energy efficiency requirements for all ships globally to reduce gas emissions from the shipping sector, through programs such as the Energy Efficiency Design Index Standards (EEDI) and the Ship Energy Efficiency Management Plan (SEEMP) [ 6 – 9 ]. However, several measures are still needed to achieve the target of 50% lower emissions by 2050 [9]. The International Energy Agency scenario proposed a number of activities that must enter into force immediately to meet the expected targets, which includes the use of alternative fuels. There are currently several studies and research connecting the maritime sector to low emissions. Nevertheless, only LNG has been widely discussed while other alternatives are hardly mentioned. Therefore, the systematic review emerges as an important methodology to quantify the number of research, regions, and authors that are addressing low carbon options for the maritime sector. The systematic review methodology is frequently used in clinical research and social sciences. However, it has been constantly used in other research fields as well [ 10 – 12 ]. We looked up several papers and reviews in the Web of Science (WoS) database with specific selected keywords related to low carbon fuels in the maritime sector to understand the proposed research questions (RQ) in statistical terms: What is the number of alternative low carbon fuel publications? (RQ1); What are the largest country contributors? (RQ2) Who have been the most important authors? (RQ3); Which journal has contributed the most in number of publications? (RQ4); and What have been the most cited alternative fuels (RQ5). This study assesses the main publications (articles and reviews) in the currently available literature on the Web of Science (WoS) database to identify the most relevant cleaner alternative fuels as decarbonization sources in the maritime sector, highlighting their advantages and disadvantages as well as identifying the gaps to overcome in future research. Moreover, we will make a descriptive statistical analysis of the selected paper to identify the most influential and productive authors, regions, and journals that have contributed highly to this hot topic over time. The article is arranged as follows. Section 2 presents the general review of vessel types, current fuel grades used, and the emissions concerns of IMO. Section 3sets out the methodology to perform the review, delineating the keywords and refining procedure. Section 4presents the analysis executed, highlighting the production over time, main journals, regions, countries’ collaborations, most cited alternative fuels as low carbon options, and the barriers to be overcome. Section 5presents the conclusions, discussion, and suggestions for the future. 2. General Review of Vessel Types and Current Fuels 2.1. Cargo Ship Classification and Propulsion Nowadays, around 52,000 cargo ships transport goods across the world. They are bulk carriers, oil tankers, and container ships [ 12 ]. Marine diesel engines are fundamentally the same as that of road vehicles, yet they are commonly bigger and work with higher efficiency. About 75% of all marine diesel engines are four-stroke; notwithstanding, 75% of the introduced power is delivered by two-stroke engines [ 13 , 14 ]. All of these ships represent 500 GW of engine capacity [ 12 ], more than all installed renewable (428 GW) and fossil (365 GW) power in Europe [ 15 ]. In order to comprehend the dimension of the shipping sector which has an exclusive demand for fossil fuels, Figure 1compares the different sources of the European electricity capacity (renewable and nonrenewable) versus the world maritime engine capacity.
Energies 2022,15, 3571 3 of 30 Energies2022,15,xFORPEERREVIEW3of31 Figure1.WorldmaritimeenginepowercomparedtoEuropeaninstalledpower(Thefigurewas constructedbasedondatacapturedfromBalcombeet.al(2019)[12]andStatista(2020)[15]. Thereareessentiallythreecategoriesofmarineengines:slowspeed,mediumspeed, andhigh‐speed,normallyclassifiedinknots(15–25knots)[12,16].Thecategorychoice dependsonthesize,enginespeed,andpurpose.Moderatespeedenginesregularly functionunder350revolutionsperminute(rpm)andhaveexceptionallylowfuel utilization.Asfarassizeisconcerned,slow‐speedenginesarethelargestenginesonthe planetthatuseheavyfueloil(HFO)forignition[13,17]. 2.2.MarineBunkerClassification Marinefuelcanbeclassifiedasdistillate,intermediate,andresidual(Table1).The distillateclassesarenamedmarinegasoil(MGO)ormarinedistillateoil(MDO)which havedifferentgrades(DMA,DMB,DMX,DMZ).Theletters“A”,“B”…“Z”,refertothe particularpropertiesundertheproductspecification,ISO8217:2017[18,19]. Theintermediatefueloil(IFO)isdividedintogrades180and380,thesenumbers correspondtothemaximumkinematicviscosityoftheresidualfuel,insquaremillimeters persecond(mm2/s)at50°C[19]. Residualfuels,alsocalledresidualmarinefuels(RMA,RMB,RMD,RME,RMG, RMK)orheavyfueloil(HFO),inparticular,areofverylowquality,lowercost,andare themostused,andindifferentgrades[19].Asthedistillateclass,theletterreferstotheir propertiesunderInternationalOrganizationforStandardization(ISO)8217:2017[19]. 0 100 200 300 400 500 600 WorldMaritimeEngineCapacity Wind PV Gas Coal Nuclear Oil Hydro Biomass Other GW Figure 1. World maritime engine power compared to European installed power (The figure was constructed based on data captured from Balcombe et.al (2019) [12] and Statista (2020) [15]. There are essentially three categories of marine engines: slow speed, medium speed, and high-speed, normally classified in knots (15–25 knots) [ 12 , 16 ]. The category choice depends on the size, engine speed, and purpose. Moderate speed engines regularly function under 350 revolutions per minute (rpm) and have exceptionally low fuel utilization. As far as size is concerned, slow-speed engines are the largest engines on the planet that use heavy fuel oil (HFO) for ignition [13,17]. 2.2. Marine Bunker Classification Marine fuel can be classified as distillate, intermediate, and residual (Table 1). The distillate classes are named marine gas oil (MGO) or marine distillate oil (MDO) which have different grades (DMA, DMB, DMX, DMZ). The letters “A”, “B” . . . “Z”, refer to the particular properties under the product specification, ISO 8217:2017 [18,19]. Table 1. Classification of marine fuels (the table was constructed based on data available in studies of Mohd Noor et al. (2018) [13] and Vermiere (2021) [19]). Marine Fuel Fuel Type Fuel Grade Common Industrial Name Definition MGO Distillate DMX, DMA, DMB, DMZ Gas oil or marine gas oil, marine diesel oil Identical to automotive diesel MDO It contains a mixture of heavy fuel oil and a higher proportion of marine gas oil. IFO Intermediate IFO 180, 380 Intermediate fuel oil such as marine diesel oil, a mixture of a higher proportion of HFO with MGO. HFO Residual RMA, RMB, RMD, RME, RMG, RMK Fuel oil or residual fuel oil The lowest grade of marine fuel. It is a residual oil, high-viscosity, and requires preheating before use.
Energies 2022,15, 3571 4 of 30 The intermediate fuel oil (IFO) is divided into grades 180 and 380, these numbers correspond to the maximum kinematic viscosity of the residual fuel, in square millimeters per second (mm2/s) at 50 ◦C [19]. Residual fuels, also called residual marine fuels (RMA, RMB, RMD, RME, RMG, RMK) or heavy fuel oil (HFO), in particular, are of very low quality, lower cost, and are the most used, and in different grades [ 19 ]. As the distillate class, the letter refers to their properties under International Organization for Standardization (ISO) 8217:2017 [19]. 2.3. International Shipping Emissions: Current and Forecast Scenarios Most CO 2 emissions from international shipping are produced by bulk carriers, container ships, and oil tankers (15%, 18%, and 11% of the total shipping emissions, respectively). The high emissions of these vessels are directly connected with the long journeys for delivering their cargo across seas and continents [12,20]. The share of consumption by fuel type is 72% of HFO, 26% of marine gas oil, and 2% of LNG [ 12 , 21 ]. The main concern of HFO consumed by the shipping sector is the sulfur content estimated at 13% of the world’s sulfur emissions [ 12 , 22 ]. SOx emissions contribute to several environmental problems, such as acidification of the water and soil, and human health issues [12,23]. The new regulations already in force imposed by Annex VI of the IMO have limited the sulfur content in Emission Control Areas (ECA) (0.1%) (0.1% m/m) and non-ECA areas (0.5% m/m), replacing the HFO with MGO or LNG [ 12 ]. The ECA areas are comprised of the Baltic Sea, North Sea, East and West coasts of the United States, and the Caribbean Sea within a distance of 200 nautical miles [ 24 ], while non-ECA areas represent the rest of the world. Concerning NOx emissions, Tier I came into force in 2000 with standards ranging from approximately 10 to 17 g/kWh, according to speed engines, Tier 2 (in 2011) fostered 20% NOx reduction below Tier 1, and Tier 3 standards applied to the NOx Emission Control Area (NECA) (The same regions of ECA areas as sulfur control) for engines installed after 1 January 201 6, with 80% NOx reduction below Tier 1 [ 25 ]. Regulation 13 of Marpol Annex VI stipulates that the emission control for all ship engines is designed for powers above 130 kilowatts (kW) [26] . Although regulations regarding SOx and NOx are stricter, the CO 2 emission reduction measures are still weak and insufficient. The International Renewable Energy Agency (IRENA) [ 27 ] recently published a report projecting the fuel demand in the shipping sector in 7.9–12.4 EJ by 2050, listing the most relevant contributing factors: global economic growth, economic growth in emerging markets, shift toward cleaner cooking fuels, strong growth in the petrochemical sector, regional trade agreements, and cleaner energy transition. 2.4. Maritime Sector and CO2Emissions CO 2 emissions in the maritime sector are forecast to reach values two-fold higher than current levels by 2050. This scenario raised IMO concerns to plan effective measures against the uncontrolled emissions of the sector. The 72nd Marine Environment Protection Committee (MEPC) resolution of the IMO set the goal of reducing emissions by half in the next three decades [24]. The scenarios in Figure 2predict the GHG emissions by 2050, those data were constructed by the IMO in the Third Greenhouse Gases Study of IMO [ 20 ], following the assumptions below: • Combinations of the Representative Concentration Pathways (RCP) (the RCPs (RCP2.6, RCP4.5, RCP6, and RCP8.5) are projections adopted by the Intergovernmental Panel of Climate Change (IPCC) which represents the range of radiative forcing caused by the GHG emissions in the year 2100 (2.6, 4.5, 6, and 8.5 W/m 2 , respectively) [ 20 ]), and the Shared Socioeconomic Pathway (SSP) (the SSPs are projections until the year 2100 utilized by the IPCC which forecasts social-economic global changes and draws the GHG emissions in five scenarios with different climate policies: SSP1 (sustainability),
Energies 2022,15, 3571 5 of 30 SSP2 (intermediate challenge), SSP3 (regional rivalry), SSP4 (inequality), and SSP5 (fossil-fueled development) [20]) in all scenarios. • Scenarios 1–4 were simulated by combining the RCP and SSP with high penetration of liquefied natural gas (LNG) and high improvement in energy efficiency (60%) over the 2012 fleet average by 2050. • Scenarios 5–8 were simulated by combining the RCP and SSP with high penetration of LNG and lower improvement in energy efficiency (40%) over the 2012 fleet average by 2050. • Scenarios 9–12 were simulated by combining the RCP and SSP with low penetration of LNG and high improvement in energy efficiency (60%) over the 2012 fleet average by 2050. • Scenarios 13–16 are the business as usual scenario (BAU) which were simulated by combining the RCP and SSP with low penetration of LNG and lower improvement in energy efficiency (40%) over the 2012 fleet average by 2050. •The dotted line is the ambitious target of 438 MtCO2eq by 2050 proposed by IMO. Energies2022,15,xFORPEERREVIEW5of31 ThescenariosinFigure2predicttheGHGemissionsby2050,thosedatawere constructedbytheIMOintheThirdGreenhouseGasesStudyofIMO[20],followingthe assumptionsbelow: CombinationsoftheRepresentativeConcentrationPathways(RCP)(theRCPs (RCP2.6,RCP4.5,RCP6,andRCP8.5)areprojectionsadoptedbythe IntergovernmentalPanelofClimateChange(IPCC)whichrepresentstherangeof radiativeforcingcausedbytheGHGemissionsintheyear2100(2.6,4.5,6,and8.5 W/m2,respectively)[20]),andtheSharedSocioeconomicPathway(SSP)(theSSPsare projectionsuntiltheyear2100utilizedbytheIPCCwhichforecastssocial‐economic globalchangesanddrawstheGHGemissionsinfivescenarioswithdifferentclimate policies:SSP1(sustainability),SSP2(intermediatechallenge),SSP3(regionalrivalry), SSP4(inequality),andSSP5(fossil‐fueleddevelopment)[20])inallscenarios. Scenarios1–4weresimulatedbycombiningtheRCPandSSPwithhighpenetration ofliquefiednaturalgas(LNG)andhighimprovementinenergyefficiency(60%)over the2012fleetaverageby2050. Scenarios5–8weresimulatedbycombiningtheRCPandSSPwithhighpenetration ofLNGandlowerimprovementinenergyefficiency(40%)overthe2012fleet averageby2050. Scenarios9–12weresimulatedbycombiningtheRCPandSSPwithlowpenetration ofLNGandhighimprovementinenergyefficiency(60%)overthe2012fleetaverage by2050. Scenarios13–16arethebusinessasusualscenario(BAU)whichweresimulatedby combiningtheRCPandSSPwithlowpenetrationofLNGandlowerimprovement inenergyefficiency(40%)overthe2012fleetaverageby2050. Thedottedlineistheambitioustargetof438MtCO2eqby2050proposedbyIMO Figure2.GHGlong‐termscenario(ThefigurewasadjustedondataavailableinThirdGreenhouse GasStudy2014)[20]. 2800 438 0 500 1000 1500 2000 2500 3000 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 Scenario1RCP8.5/SSP5 Scenario2RCP6.0/SSP1 Scenario3RCP4.5/SSP3 Scenario4RCP2.6/SSP4 Scenario5RCP8.5/SSP5 Scenario6RCP6.0/SSP1 Scenario7RCP4.5/SSP3 Scenario8RCP2.6/SSP4 Scenario9RCP8.5/SSP5 Scenario10RCP6.0/SSP1 Scenario11RCP4.5/SSP3 Scenario12RCP2.6/SSP4 Scenario(BAU)13RCP8.5/SSP5 Scenario14(BAU)RCP6.0/SSP1 Scenario15(BAU)RCP4.5/SSP3 Scenario16(BAU)RCP2.6/SSP4 IMO MtCO 2 eq Figure 2. GHG long-term scenario (The figure was adjusted on data available in Third Greenhouse Gas Study 2014) [20]. Recently the IMO assumed that the measures to reduce emissions must be implemented as early as possible for this century, setting ambition levels and guiding principles [24]. GHG reductions are still only based on the Energy Efficiency Design Index (EEDI) and the Ship Energy Efficiency Management Plan (SEEMP), which are in line with the technical and operational categories [ 28 , 29 ]. Technical measures focus on design and improvement in energy efficiency, propulsion, power system, and low carbon fuels. Some actions can be implemented through retrofitting of existing ships, while others only in
Energies 2022,15, 3571 6 of 30 new ships [ 28 ]. Even so, alternatives are required and the sector has turned its attention to alternative options. Next, we outline the methods of the approach and the most recent studies that cite alternative sources as one of the decarbonizing measures to be applied in the mari time sect or. 3. Material and Methods At the moment there are several studies regarding low carbon alternative fuels, nevertheless few of them apply to the maritime sector. To highlight important articles and reviews, a systematic analysis was made of the Web of Knowledge online database service by Thomson Reuters Inc. Studies were adapted [ 30 ] from the similar study already available in the literature [ 31 ]. Based on a combination of words to find papers which mention cleaner fuels as an alternative to decarbonize the maritime sector. Refining The refining method will be elaborated on in 3 steps. The 1st step is taken in the advanced search by applying the field tag displayed in Table 2below. Table 2. Keywords refining. 1st Step of Refining Keyword Research TS = (renewable energy or biofuels or advanced biofuel or alternative fuels or low carbon fuel or biomethanol or bioethanol or biodiesel or methyl ester or biogas or bio LNG or bio liquefied natural gas or Hydrotreated Vegetable oil or renewable fuel or pyrolysis oil or Fischer Tropsch or hydrogen or hydrothermal liquefaction or batteries or state of the art technologies) and TS = (decarb onization or low carbon emissions or decarbonize or greenhouse gases reductions or GHG reductions or greenhouse gases emissions or GHG emissions) and TS = (Mariti me sector or shipping sector or international shipping sector or maritime transportation or decarbonize international maritime or alternative fuel for marine applications or marine diesel engines) TS represents the topic and the binary variables OR, AND relate the keywords with the intention of finding papers on the Web of Science database. The 2nd step is to relate only papers and reviews, in the English, during the period from January 2000 to January 2022. The 3rd step is conducted manually, the papers which approach alternative fuels as cleaner sources for the maritime decarbonization. 4. Result and Discussion 4.1. Selected Papers and Descriptive Statistics Figure 3displays the three steps suggested, as well as their research criteria. The first selected studies reached an overall combination of 328 articles, reviews, proceedings papers, and book chapters, with papers and reviews accounting for 91% of the total. Nevertheless, it was necessary to carry our manual refining for the decarbonization of the maritime sector and alternative and low carbon fuels. After manual refining, the RQ1 can be answered, where 91 papers and 12 reviews (Figure 3) were selected as a baseline for part of the state of the art. The growth in publications in 2018 (Figure 4) was evident, from only 3 (2.91% of total) in 2017 to 29 (28.16% of total) in 2021. The years from 2020 to 2022 correspond to 65% of the papers concerned, driven by the IMO’s recent mandatory requirements for greenhouse gas emissions which gained prominence due to real intentions of reduction recently.
Energies 2022,15, 3571 7 of 30 Energies2022,15,xFORPEERREVIEW7of31 Nevertheless,itwasnecessarytocarryourmanualrefiningforthedecarbonizationofthe maritimesectorandalternativeandlowcarbonfuels. Aftermanualrefining,theRQ1canbeanswered,where91papersand12reviews (Figure3)wereselectedasabaselineforpartofthestateoftheart.Thegrowthin publicationsin2018(Figure4)wasevident,fromonly3(2.91%oftotal)in2017to29 (28.16%oftotal)in2021.Theyearsfrom2020to2022correspondto65%ofthepapers concerned,drivenbytheIMO’srecentmandatoryrequirementsforgreenhousegas emissionswhichgainedprominenceduetorealintentionsofreductionrecently. Figure3.Relateddocumentsonrefinedsteps. Figure4.Publicationsovertheyears. WefindtheanswertoRQ2intheselectedworks,whichhighlightthehigh contributionoftheEuropeancountries(57%)(Table3),probablydrivenbythestrictrules inplacesince2015intheBaltic,theNorthSea,andNorthAmericancoastregardingSOx andNOx.Moreover,Europehasahighenergydependence,thusthereisacommitment toreducenotonlytheemissionsassociatedwithfossilsourcesusedinthemaritimesector 1stStep‐328documents ● Researchcriteria: Combinationofkeywords WebofScienceDataBase ● Period:Januaryof2000 toJanuaryof2022 2ndStep‐297documents ● Researchcriteria: ● Types:Articles,Reviews ● Language:English 3rdStep‐103documents ● ExclusionCriteria: ● DonotaddressMaritime Transportation Decarbonizationand alternativefueluse(194 paperselminatedafter abstract,titleandkey wordsread) 0.00 5.00 10.00 15.00 20.00 25.00 30.00 0 5 10 15 20 25 30 35 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Numberofpublications % Figure 3. Related documents on refined steps. Energies2022,15,xFORPEERREVIEW7of31 Nevertheless,itwasnecessarytocarryourmanualrefiningforthedecarbonizationofthe maritimesectorandalternativeandlowcarbonfuels. Aftermanualrefining,theRQ1canbeanswered,where91papersand12reviews (Figure3)wereselectedasabaselineforpartofthestateoftheart.Thegrowthin publicationsin2018(Figure4)wasevident,fromonly3(2.91%oftotal)in2017to29 (28.16%oftotal)in2021.Theyearsfrom2020to2022correspondto65%ofthepapers concerned,drivenbytheIMO’srecentmandatoryrequirementsforgreenhousegas emissionswhichgainedprominenceduetorealintentionsofreductionrecently. Figure3.Relateddocumentsonrefinedsteps. Figure4.Publicationsovertheyears. WefindtheanswertoRQ2intheselectedworks,whichhighlightthehigh contributionoftheEuropeancountries(57%)(Table3),probablydrivenbythestrictrules inplacesince2015intheBaltic,theNorthSea,andNorthAmericancoastregardingSOx andNOx.Moreover,Europehasahighenergydependence,thusthereisacommitment toreducenotonlytheemissionsassociatedwithfossilsourcesusedinthemaritimesector 1stStep‐328documents ● Researchcriteria: Combinationofkeywords WebofScienceDataBase ● Period:Januaryof2000 toJanuaryof2022 2ndStep‐297documents ● Researchcriteria: ● Types:Articles,Reviews ● Language:English 3rdStep‐103documents ● ExclusionCriteria: ● DonotaddressMaritime Transportation Decarbonizationand alternativefueluse(194 paperselminatedafter abstract,titleandkey wordsread) 0.00 5.00 10.00 15.00 20.00 25.00 30.00 0 5 10 15 20 25 30 35 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Numberofpublications % Figure 4. Publications over the years. We find the answer to RQ2 in the selected works, which highlight the high contribution of the European countries (57%) (Table 3), probably driven by the strict rules in place since 2015 in the Baltic, the North Sea, and North American coast regarding SOx and NOx. Moreover, Europe has a high energy dependence, thus there is a commitment to reduce not only the emissions associated with fossil sources used in the maritime sector but also to reduce the dependence on external energy. Regarding the ranking by country, 41 countries showed contributions, the first 5 countries accounting for 49% of the total. England and the USA accounted for the highest proportion (18%), followed by China and Norway (14%),
Energies 2022,15, 3571 8 of 30 Germany and Sweden (12%), and the Netherlands (5%). The remaining countries accounted for 4% or less. Table 3. Number of studies per country. Rank Countries % Countries % Position Region % 1st England 9 Greece 1 1st Europe 57 USA 9 Northern Ireland 1 2nd Asia 21 2nd China 7 Poland 1 3rd North America 12 Norway 7 Japan 1 4th South America 4 3rd Germany 6 Austria 1 5th Oceania 3 Sweden 6 Bosnia 1 6th Africa 2 4rd Netherlands 5 Cyprus 1 7th Middle East 1 5th Singapore 4 Denmark 1 Spain 4 Iceland 1 Brazil 4 Lithuania 1 6th Turkey 3 Malta 1 Italy 3 Montenegro 1 Canada 3 Scotland 1 7th South Korea 2 Serbia 1 Taiwan 2 Saudi Arabia 1 Croatia 2 United Arab Emirates 1 Finland 2 Fiji 1 Ireland 2 South Africa 1 Australia 2 Nigeria 1 8th India 1 Egypt 1 Malaysia 1 Total 100% Concerning authors (RQ3), a total of 446 authors wrote 103 articles (Appendix A). Four percent of the articles were written by individual authors, while 19.42% were written by two authors, 16.50% by three authors, and 60.19% involved a team of four or more authors (Table 4). Furthermore, Table 5shows the list of the most productive authors. Linstad, E. and Xing, H. wrote 3 articles each. At the same time, the other authors published either two papers or one paper each. Therefore, Bouman, EA. and Balcombe, P. have the most cited papers—7% and 14% respectively—out of a total of 1600 cited papers. Table 4. Number of authors per paper. Number of Authors per Paper Number of Papers % 13 1 1 12 1 1 11 1 1 10 3 3 9 1 1 8 1 1 7 9 9 6 9 9 5 11 11 4 25 24 3 17 16 2 20 19 1 4 4 Total 103 100
Energies 2022,15, 3571 9 of 30 Table 5. Most productive and cited authors. Authors Number of Papers %Times Cited %Citations per Paper Authors Number of Papers %Times Cited %Citations per Paper Lindstad, E 3 3% 26 2% 9 Law, L 1 1% 0 0% 0 Xing, H 3 3% 37 2% 12 Liu, J 1 1% 0 0% 0 Ampah, JD 2 2% 6 0% 3 Mallouppas, G 1 1% 5 0% 5 Bach, H 2 2% 19 1% 10 Mukherjee, A 1 1% 2 0% 2 Balcombe, P 2 2% 109 7% 55 Mwangi, JK 1 1% 29 2% 29 Carvalho, F 2 2% 1 0% 1 Nabi, MN 1 1% 8 1% 8 Gabina, G 2 2% 35 2% 18 Nair, A 1 1% 2 0% 2 Lin, CY 2 2% 39 2% 20 Nikolic, D 1 1% 2 0% 2 Muller-Casseres, E 2 2% 5 0% 3 Nine, RD 1 1% 3 0% 3 Percic, M 2 2% 26 2% 13 Nuchturee, C 1 1% 26 2% 26 Sari, A 2 2% 1 0% 1 Ogunkunle, O 1 1% 16 1% 16 Shannina, M 2 2% 28 2% 14 Ortiz-Imedio, R 1 1% 3 0% 3 Armstrong, VN 1 1% 45 3% 45 Pan, HS 1 1% 32 2% 32 Atilhan, S 1 1% 22 1% 22 Peng, WH 1 1% 8 1% 8 Awoyomi, A 1 1% 4 0% 4 Petzold, A 1 1% 53 3% 53 Ayvali, T 1 1% 0 0% 0 Pfeifer, A 1 1% 13 1% 13 ben Brahim 1 1% 14 1% 14 Popp, L 1 1% 0 0% 0 Bicer, Y 1 1% 30 2% 30 Prasad, RD 1 1% 2 0% 2 Bouman, EA 1 1% 226 14% 226 Prussi, M 1 1% 14 1% 14 Cassar, MP 1 1% 0 0% 0 Righi, M 1 1% 38 2% 38 Chen, ZS 1 1% 0 0% 0 Rizzo, AM 1 1% 0 0% 0 Chiong, MC 1 1% 1 0% 1 Rodriguez, CG 1 1% 0 0% 0 Choi, W 1 1% 16 1% 16 Schonsteiner, K 1 1% 10 1% 10 Christodoulou, A 1 1% 1 0% 1 Serra, P 1 1% 15 1% 15 Corbin, JC 1 1% 14 1% 14 Spoof-Tuomi, K 1 1% 11 1% 11 Cortez, L 1 1% 0 0% 0 Styhre, L 1 1% 68 4% 68 Czermanski, E 1 1% 4 0% 4 Taccani, R 1 1% 4 0% 4 Elkafas, AG 1 1% 3 0% 3 Tan, ECD 1 1% 1 0% 1 Gallo, M 1 1% 5 0% 5 Tanzer, SE 1 1% 20 1% 20 Garcia, B 1 1% 0 0% 0 Torres-Garcia, M 1 1% 11 1% 11 Ghenai, C 1 1% 43 3% 43 Trivyza, NL 1 1% 0 0% 0 Gilbert, P 1 1% 71 4% 71 Tvedten, IO 1 1% 0 0% 0 Gonzalez-Arias, J 1 1% 0 0% 0 Tzannatos, E 1 1% 5 0% 5 Gysel, NR 1 1% 11 1% 11 Ushakov, S 1 1% 7 0% 7 Hagos, DA 1 1% 29 2% 29 van der Kroft 1 1% 0 0% 0 Hansson, J 1 1% 29 2% 29 Wahl, J 1 1% 0 0% 0 Helgason, R1 1 1% 11 1% 11 Wang, H 1 1% 4 0% 4 Herdzik, J 1 1% 0 0% 0 Wang, ZC 1 1% 2 0% 2 Hirdaris, SE 1 1% 47 3% 47 Winebrake, JJ 1 1% 5 0% 5 Horvath, S 1 1% 33 2% 33 Winnes, H 1 1% 86 5% 86 Hwang, SS 1 1% 6 0% 6 Wu, P 1 1% 17 1% 17 Inal, OB 1 1% 26 2% 26 Yildirim Peksen, D 1 1% 0 0% 0 Kesieme, U 1 1% 27 2% 27 Yusuf, AA 1 1% 0 0% 0 Khan, MY 1 1% 23 1% 23 Zahraee, SM 1 1% 0 0% 0 Kistner, L 1 1% 1 0% 1 Total 103 100% 1600 100% Table 6highlights the frequency of the papers published in the journals (RQ4). The Journal of Cleaner Production,Sustainability, and Transportation Research Part D stand out, with twenty-one percent of all published papers (21%), followed by Energies and Energy (12%), the International Journal of Hydrogen Energy, and Renewable & Sustainable Energy Reviews (10%). The remaining journals published only four papers or less. The first ten papers (10% of the total) listed in Table 7corresponded to 768 citations (48% of the total) which is almost half of the selected documents, probably for the reason they are one of the first references for alternative fuel use as an option to reduce GHG emissions and other pollutant gases. The major findings from those studies are summarized in sequence (Table 7).
Energies 2022,15, 3571 16 of 30 Table 8. GHG emissions of different fuels (the table was constructed based on data available in Balcombe et.al (2019) studies [12]. Fuel Types gCO2eq/kWh LNG 580–870 Hydrogen 113–997 Biodiesel 90–430 Methanol 50–290 Pyrolysis Oil 250–340 FT-diesel 50 HVO 210–400 Ethanol 140–250 SVO 290 Advanced biofuels, such as advanced bio-methanol, bio-methane, FT-diesel, and pyrolysis oil can impact the CO 2 eq carbon footprint further (Table 8) due to the fact that they do not compete with food and feed production since the feedstock comes mainly from waste [12]. The studies by Bouman et al. (2017) [ 28 ] presented biofuels as displaying the biggest potential for reducing GHG emissions in the maritime sector. Furthermore, their biodegradability is an advantage regarding accidental spills [ 12 , 68 ]. Serra and Fancello (2020) [ 69 ] cited the advantages of biofuels in connection with their biodegradability. However, the authors highlighted the attention of constraints on the emissions associated with direct and indirect land use. In studies by Law et al. [ 70 ] the importance of the life cycle assessment (well-to-wake) over the alternative fuel use is mentioned. The entire supply chain must ensure that all the impacts some fuels can cause and a well-to-wake energy assessment of marine fuels still lacking consideration in literature be accounted for. From several biofuel types and routes, biodiesel and bio-methanol were cited as good options in terms of costs, availability, and level of technology. However, the main problems concern NOx, SOx, and PM. The author also concluded that hydrogen and ammonia are the worst options due to the overall energy consumed and high costs of production. Prussi et al. [ 71 ] also mentioned that zero-emission in alternative fuels only occurs from a tank-to-wake perspective, since many emissions and impacts may occur before their production and other GHG methodologies must be used (well-to-tank). The author also commented that if alternative options do not come from a renewable basis, the carbon footprint can be higher than the conventional fossil sources already used. The supply chain of alternative fuels assessment is a determinant to verify how clean some fuels can be, and the full life cycle assessment is the most important tool cited by some authors to quantify the many impacts caused by different energy source options. 4.1.11. Maritime Biofuel Use and Barriers The new mandatory rules concerning maritime transport can increase the cost considerably for the sector by around USD 60 billion per annum. The fuel expenditure represents almost half of the operating cost, and it can reflect an increase of 10% of the equivalent of the twenty-foot unit (TEU) cost transported [69,72]. Only a few alternative options are currently available and LNG appears to be the best transitory option. However, the paradigm is in bunker suppliers, who do not want to make investments until sufficient demand is guaranteed, and the ship-owners do not make investments if there are no refueling points [ 69 , 73 ]. This observation can also apply to the alternative fuel options. The search for new and mandatory measures has awakened the concerns about the rebound effect they can produce [ 69 , 74 ]. For example, some studies suggest that, if the new ECA regulations are applied in the Mediterranean Sea, they can increase the cost
Energies 2022,15, 3571 17 of 30 of maritime transport by about 6.95 EUR/GJ [ 69 , 75 , 76 ] and foster a modal shift to land transport, contributing to increasing CO2emissions [64,69]. Another real problem is the split of incentives between shipowners and charterers. The cost of investments in cleaner alternatives is only feasible if the former directly operate their ships or make better agreements with charterers, splitting the economic advantages and disadvantages of greener decisions. As agreed between ship-owners and the port operators, GHG emission reduction is subject to three main kinds of risks: business, technical, and external [ 69 , 77 ]. The first concerns the payback period, the second is attributed to the lack of reliability of the rules applied, and the third refers to the cost of fuel, policy, and regulations. An important observation has been made by Machado (2019) in Brazil [ 78 ]. The implementation of the new rules concerning 0.5% less sulfur emissions can impact the cost of the diesel used in road transport. Due to this fact, distilled marine fuel is similar to the diesel used in road transportation. The high demand can impact the lack of fuel and consequently increase the price. It can have the same impact on first-generation biofuel, which is already being used in blends for road transport in many parts of the world. This concern mentioned before opens up the way for advanced biofuels and alternative fuel exploration. However, the low development of this source makes it highly expensive and discourages its use. 5. Conclusions and Suggestions for the Future The study selected high-standard papers in the Web of Science database to identify the contribution of academia in the literature to the use of alternative fuels in the shipping sector as a low carbon option. Several assessments was done to analyze factors as number of papers, the most authors, the main regions and how cited those articles and reviews have been employed to contribute to reduce the GHG emissions in maritime sector. The research was important for understanding which resources have contributed most to the scenario, how they have developed, what is expected for the future, and why they are important. Based on keyword combination, 103 articles were found that mention biofuels or low carbon alternatives used in the maritime sector. The LNG is undoubtedly the main low carbon alternative with many ships already operating with this source in the world. Eighty-eight percent of the papers referred to LNG as an important source in the maritime sector for GHG reduction. Moreover, it can significantly reduce other emissions, such as SO x , NO x , and PM. Nevertheless, the methane slip (methane that escapes into the atmosphere) is one of the drawbacks due to its high GHG potential. Bio-LNG could be a potential option, but production is still too low to meet the high demand in the shipping sector. Hydrogen is one of the most cited options (16.2%). In a tank-to-wheel assessment, H 2 from fossil sources has nil GHG emissions, which can also be highly carbon-intensive when analyzed from a well-to-wheel perspective. Renewable hydrogen or green hydrogen has been widely discussed for the mediumand long-term, but the current stage of development and use in the shipping sector is still low. Biodiesel is a renewable and low carbon source, which represented 14.5% of total mentions. This option, together with HVO (3.8%) and SVO (3.4%) are sources that can be blended into the current marine engines without further modification. Nevertheless, the main feedstock comes from food/feed sources and from deforested areas, which can raise other issues. Methanol accounted for 23.8% of mentions in the assessed studies. The largest barrier is its production, which is consolidated only through fossil resources, and a modest number of vessels are already running on this alternative fuel. A new recent resource widely discussed in academia is ammonia. This fuel (fossil or renewable) is capable to be employed in ICE or full cells. The resource received 9.8%
Energies 2022,15, 3571 18 of 30 of mentions in the assessed papers. However, it still appears as a promising hope for the future since it is still limited to the research field. The advanced route of alternative fuel production had an expressionless contribution. Pyrolysis oil and Fischer–Tropsch diesel accounted for 5.1 and 4.3% of citations, respectively, in the selected papers. Although they have an expressive contribution to GHG emission reductions, the drawback is the low development level of those technologies, lack of standards, and high cost of production. In all cases mentioned before, the cleaner fuels are still not sufficiently representativity in the maritime sector. Probably due to the lack of incentives from the production and consumer demand. Moreover, there is a lot of resistance from the shipping industry. The study concluded that several barriers, such as low technology development, cost and accessibility, shipping industry, charterer acceptance, and lack of homogeneous regulations over international waters, hamper the development of new fuel sources. Some alternatives can be used as a blend in current fuels, such as LNG, biodiesel, and methanol. Moreover, lignocellulosic residues can increase their availability without constraining food and feed production, nor the competition with biofuels already used in the road sector [63]. In terms of trends, Ampah et al. [ 31 ] concluded, that LNG has been the most investigated alternative source, mainly driven by the fact that it is an abundant cleaner fuel; furthermore, their production, transportation, storage, and final use hold consolidated technologies with cost-competitiveness. However, the author also concluded that there is a new research tendency over methanol, ammonia, and hydrogen. Top experts believe that implementation may be difficult due to the associated high cost. Nevertheless, high cost compared to what? It is clear that fossil fuel still accounts for expressive subsidies in the world, and the maritime sector uses the cheapest fuel compared to other transport modes. Consequently, the question one must ask is what price will we pay in the future? This study has been important to show the lack of in-depth studies on cleaner fuel options in the maritime sector. The private sector and governments must start acting now to stimulate research and development, which, consequently, will soon spread to the shipping industry. The study review herein has not included practical studies on the alternative production and tests, where all of them are limited only in theory. Practical studies are essential to gain the reliability and confidence of the shipping industry. Other studies, i.e., on the break-even level of oil price, could be carried out to assay at which price level of oil would the cleaner sources be comparable to the current fossil fuels. The development of the carbon market will also be an important measure for stimulating maritime sector decarbonization. Author Contributions: V.A.d.S.: conceptualization, methodology, investigation, writing—original draft, writing—review and editing; P.P.d.S.: resources, conceptualization, validation, supervision, writing—reviewand editing; L.M.V.S.: resources, conceptualization, validation, supervision, writing— review and editing. All authors have read and agreed to the published version of the manuscript. Funding: This Research was funded by the Science and Technology Foundation (FCT), Ministry of Science and Higher Education (MCTES), European Social Fund (FSE), and Europe Union (EU), under the grant number PD/BD/142848/2018. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable.
Energies 2022,15, 3571 19 of 30 Acknowledgments: The author would like to acknowledge the financial support received from the Science and Technology Foundation (FCT), Ministry of Science and Higher Education (MCTES), European Social Fund (FSE), and Europe Union (EU), under the grant number PD/BD/142848/2018. Patrícia P. Silva acknowledges that this work has been partially supported by the European Regional Development Fund in the framework of COMPETE 2020 Programme and the FCT though project T4ENERTEC (POCI-01-0145-FEDER-029820), by the FCT under projects UID/MULTI/00308/2020 and UIDB/05037/2020 and by the Energy for Sustainability Initiative of the University of Coimbra. Conflicts of Interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Abbreviations €Euros BAU Business-as-usual Bio-LNG Bio liquefied natural gas Bio-SNG Bio synthetic natural gas CO2Carbon dioxide CH4Methane DMA Destilate marine oil A DMB Destilate marine oil B DMX Distillate marine oil X DMZ Distillate marine oil Z EEDI Energy Efficiency Design Index FT-diesel Fischer–Tropsch diesel gCO2eq Gram of equivalent carbon dioxide GHG Greenhouse gases GHG Greenhouse gases GJ Gigajoule GW Gigawatt HFO Heavy fuel oil HVO Hydrotreated vegetable oil ICE Internal combustion engine IEA International Energy Agency IFO Intermediate fuel oil IGC International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk IRENA International Renewable Energy Agency IMF Intermediate marine fuel IMO International Maritime Organization ISO International Organization for Standardization kWh Kilowatt-hour LNG Liquified natural gas Marpol International Convention for the Prevention of Pollution from Ships MBOE Million barrel of oil equivalent MCDA Multi-criteria decision analysis MDO Marine distillate oil LNG Liquified natural gas MBOE Million Barrel of Oil Equivalent MCDA multi-criteria decision analysis MDO Marine distillate oil MtCO2eq Million tons of equivalent carbon dioxide N2O Nitrous oxide RMA Residue marine oil A RMB Residual marine oil B RMD Residual marine oil D RME Residual marine oil E
Energies 2022,15, 3571 20 of 30 RMF Residue marine Fuel RMG Residual marine oil G RMK Residual marine oil K RPM Revolution per minute RQ Research question s Second SECA Sulfur Emissions Control Area SEEMP Ship Energy Efficiency Management Plan SOx Sulfur oxide SVO Straight vegetable oil SSP Shared socio-economic pathway t Tonne TEU Twenty equivalent units USA United States of America USD US Dollar WoS Web of Science Appendix A Table A1. Selected articles. Number Article Title Authors 1Retrofitting towards a greener marine shipping future: Reassembling ship fuels and liquefied natural gas in Norway [79] 2 Study on characteristics of marine heavy fuel oil and low carbon alcohol blended fuels at different temperatures [80] 3Life cycle assessment of diesel and hydrogen power systems in tugboats [81] 4Carbon abatement cost of hydrogen-based synthetic fuels-A general framework exemplarily applied to the maritime sector [82] 5Decision support methods for sustainable ship energy systems: A state-of-the-art review [83] 6Biogas upgrading to biomethane as a local source of renewable energy to power light marine transport: Profitability analysis for the county of Cornwall [84] 7Blending of Hydrothermal Liquefaction Biocrude with Residual Marine Fuel: An Experimental Assessment [85] 8Possibilities of Ammonia as Both Fuel and NOx Reductant in Marine Engines: A Numerical Study [86] 9Influence of waste oil-biodiesel on toxic pollutants from marine engine coupled with emission reduction measures at various loads [87] 10 Global futures of trade impacting the challenge to decarbonize the international shipping sector [88] 11 Prospects for carbon-neutral maritime fuel production in Brazil [89] 12 A Comparison of Alternative Fuels for Shipping in Terms of Lifecycle Energy and Cost [70] 13 Reduction of maritime GHG emissions and the potential role of E-fuels [90] 14 Particle-Gaseous pollutant emissions and cost of global biomass supply chain via maritime transportation: Full-scale synergy model [91] 15 Reviewing two decades of cleaner alternative marine fuels: Towards IMO’s decarbonization of the maritime transport sector [31] 16 Challenges and opportunities of marine propulsion with alternative fuels [92] 17 Techno-economic and Environmental Comparison of Internal Combustion Engines and Solid Oxide Fuel Cells for Ship Applications [93]
Energies 2022,15, 3571 21 of 30 Table A1. Cont. Number Article Title Authors 18 A Study into the Availability, Costs and GHG Reduction in Drop-In Biofuels for Shipping under Different Regimes between 2020 and 2050 [94] 19 Environmental impact assessment of hydrogen-based auxiliary power system onboard [95] 20 Biofuels for Maritime Transportation: A Spatial, Techno-Economic, and Logistic Analysis in Brazil, Europe, South Africa, and the USA [96] 21 Perspective Use of Fast Pyrolysis Bio-Oil (FPBO) in Maritime Transport: The Case of Brazil [97] 22 Power-to-Ships: Future electricity and hydrogen demands for shipping on the Atlantic coast of Europe in 2050 [98] 23 How can LNG-fuelled ships meet decarbonisation targets? An environmental and economic analysis [46] 24 Technical reliability of shipboard technologies for the application of alternative fuels [99] 25 Decarbonization of Marine Fuels-The Future of Shipping [100] 26 Biofuel Options for Marine Applications: Technoeconomic and Life-Cycle Analyses [101] 27 Alternative fuel options for low carbon maritime transportation: Pathways to 2050 [102] 28 The Position of Ammonia in Decarbonising Maritime Industry: An Overview and Perspectives: Part I Technological advantages and the momentum towards ammonia-propelled shipping [103] 29 Blending new and old in sustainability transitions: Technological alignment between fossil fuels and biofuels in Norwegian coastal shipping [104] 30 Liquefied Natural Gas as Ship Fuel: A Maltese Regulatory Gap Analysis [105] 31 Can Market-based Measures Stimulate Investments in Green Technologies for the Abatement of GHG Emissions from Shipping? A Review of Proposed Market-based Measures [106] 32 Decarbonization in Shipping Industry: A Review of Research, Technology Development, and Innovation Proposals [107] 33 Potential and limiting factors in the use of alternative fuels in the European maritime sector [71] 34 Production of alternative marine fuels in Brazil: An integrated assessment perspective [43] 35 Green hydrogen as an alternative fuel for the shipping industry [108] 36 Net Zero for the International Shipping Sector? An Analysis of the Implementation and Regulatory Challenges of the IMO Strategy on Reduction of GHG Emissions [109] 37 Analysis and Modeling the Energy System of a Chemical Tanker by LEAP [110] 38 Fuel Cell Power Systems for Maritime Applications: Progress and Perspectives [111] 39 Energy efficiency of integrated electric propulsion for ships—A review [112] 40 Life-cycle cost assessment of alternative marine fuels to reduce the carbon footprint in short-sea shipping: A case study of Croatia [113] 41 A comprehensive review on countermeasures for CO2emissions from ships [114] 42 Numerical analysis of economic and environmental benefits of marine fuel conversion from diesel oil to natural gas for container ships [115] 43 A Perspective on Biofuels Use and CCS for GHG Mitigation in the Marine Sector [116] 44 Decarbonizing Maritime Transport: The Importance of Engine Technology and Regulations for LNG to Serve as a Transition Fuel [117] 45 Renewable Ammonia as an Energy Fuel for Ocean Exploration and Transportation [118]
Energies 2022,15, 3571 22 of 30 Table A1. Cont. Number Article Title Authors 46 Exhaust emissions and engine performance analysis of a marine diesel engine fuelled with Parinari polyandra biodiesel-diesel blends [119] 47 Comprehensive analysis of the air quality impacts of switching a marine vessel from diesel fuel to natural gas [120] 48 Decarbonising the critical sectors of aviation, shipping, road freight and industry to limit warming to 1.5–2 ◦C[121] 49 Implementing maritime battery-electric and hydrogen solutions: A technological innovation systems analysis [122] 50 Life-cycle cost assessments of different power system configurations to reduce the carbon footprint in the Croatian short-sea shipping sector [123] 51 Investigation to meet China II emission legislation for marine diesel engine with diesel methanol compound combustion technology [124] 52 Life Cycle Assessment of Alternative Ship Fuels for Coastal Ferry Operating in Republic of Korea [125] 53 Characterization of Biomethanol-Biodiesel-Diesel Blends as Alternative Fuel for Marine Applications [126] 54 Assessment of fuel cell types for ships: Based on multi-criteria decision analysis [127] 55 An evaluation of the cost-competitiveness of maritime fuels—a comparison of heavy fuel oil and methanol (renewable and natural gas) in Iceland [128] 56 Vegetable oils as renewable fuels for power plants based on low and medium speed diesel engines [129] 57 Process and Economic Evaluation of an Onboard Capture System for LNG-Fueled CO2Carriers [130] 58 Sustainability in Maritime Sector: Waste Management Alternatives Evaluated in a Circular Carbon Economy Perspective [131] 59 The Potential Role of Ammonia as Marine Fuel-Based on Energy Systems Modeling and Multi-Criteria Decision Analysis [66] 60 Towards the IMO’s GHG Goals: A Critical Overview of the Perspectives and Challenges of the Main Options for Decarbonizing International Shipping [69] 61 LNG and Cruise Ships, an Easy Way to Fulfil Regulations-Versus the Need for Reducing GHG Emissions [132] 62 Environmental and Economic Evaluation of Fuel Choices for Short Sea Shipping [133] 63 Decarbonization of Maritime Transport: Analysis of External Costs [56] 64 Challenges and opportunities of zero emission shipping in smart islands: A study of zero emission ferry lines [134] 65 Hybrid fuel cell and battery propulsion system modelling and multi-objective optimisation for a coastal ferry [135] 66 Characterization of particulate matter emitted by a marine engine operated with liquefied natural gas and diesel fuels [136] 67 High energy density storage of gaseous marine fuels: An innovative concept and its application to a hydrogen powered ferry [137] 68 Pathways to climate-neutral shipping: A Danish case study [65] 69 Lignocellulosic marine biofuel: Technoeconomic and environmental assessment for production in Brazil and Sweden [53] 70 Hybrid solar PV/PEM fuel Cell/Diesel Generator power system for cruise ship: A case study in Stockholm, Sweden [36]
Energies 2022,15, 3571 23 of 30 Table A1. Cont. Number Article Title Authors 71 Pollution Tradeoffs for Conventional and Natural Gas-Based Marine Fuels [138] 72 Biofuel as an alternative shipping fuel: technological, environmental and economic assessment [4] 73 Fuel demand and emissions for maritime sector in Fiji: Current status and low-carbon strategies [139] 74 How to decarbonise international shipping: Options for fuels, technologies and policies [12] 75 Performance of marine diesel engine in propulsion mode with a waste oil-based alternative fuel [140] 76 Well-to-wheel assessment of natural gas vehicles and their fuel supply infrastructures—Perspectives on gas in transport in Denmark [141] 77 Well-to-wheel greenhouse gas emissions of battery electric vehicles in countries dependent on the import of fuels through maritime transportation: A South Korean case study [142] 78 Alternative fuels for shipping : Optimising fleet composition under environmental and economic constraints [143] 79 Techno-economic analysis of a decarbonized shipping sector: Technology suggestions for a fleet in 2030 and 2040 [52] 80 Environmental impact categories of hydrogen and ammonia driven transoceanic maritime vehicles: A comparative evaluation [42] 81 Assessment of full life-cycle air emissions of alternative shipping fuels [33] 82 Application of Alternative Maritime Power (AMP) Supply to Cruise Port [144] 83 Global energy scenarios and their implications for future shipped trade [145] 84 Greenhouse gas emissions from ships in ports—Case studies in four continents [34] 85 State-of-the-art technologies, measures, and potential for reducing GHG emissions from shipping—A review [28] 86 Waste oil-based alternative fuels for marine diesel engines [146] 87 Evaluation of pollutant emissions from two-stroke marine diesel engine fueled with biodiesel produced from various waste oils and diesel blends [147] 88 Sustainable transport by use of alternative marine and aviation fuels-A well-to-tank analysis to assess interactions with Singapore’s energy system [148] 89 Reducing GHG emissions from ships in port areas [32] 90 Emission Reductions of Nitrogen Oxides, Particulate Matter and Polycyclic Aromatic Hydrocarbons by Using Microalgae Biodiesel, Butanol and Water in Diesel Engine [149] 91 Effect of hydrogen addition on criteria and greenhouse gas emissions for a marine diesel engine [150] 92 Impact of Sugarcane Renewable Fuel on In-Use Gaseous and Particulate Matter Emissions from a Marine Vessel [151] 93 Considerations on the potential use of Nuclear Small Modular Reactor (SMR) technology for merchant marine propulsion [37] 94 Vessel optimisation for low carbon shipping [35] 95 Effects of Biodiesel Blend on Marine Fuel Characteristics for Marine Vessels [44] 96 Strategies for promoting biodiesel use in marine vessels [45] 97 Natural gas as a fuel alternative for sustainable domestic passenger shipping in Greece [152] 98 Emission characteristics of GTL fuel as an alternative to conventional marine gas oil [153]
Energies 2022,15, 3571 24 of 30 Table A1. Cont. Number Article Title Authors 99 Impact of Algae Biofuel on In-Use Gaseous and Particulate Emissions from a Marine Vessel [154] 100 Investigation of engine performance and emissions of a diesel engine with a blend of marine gas oil and synthetic diesel fuel [155] 101 Operation of Marine Diesel Engines on Biogenic Fuels: Modification of Emissions and Resulting Climate Effects [38] 102 Climate Impact of Biofuels in Shipping: Global Model Studies of the Aerosol Indirect Effect [39] 103 Use of soy-derived fuel for environmental impact reduction in marine engine applications [156] References 1. Sirimanne, S.N.; Hoffman, J.; Juan, W.; Asariotis, R.; Assaf, M.; Ayala, G.; Benamara, H.; Chantrel, D.; Hoffmann, J.; Premti, A. Review of Maritime Transport 2019; UNCTAD: New York, NY, USA, 2019; ISBN 978-92-112858-8. 2. IEA. Commentary: International Maritime Organization Agrees to First Long-Term Plan to Curb Emissions. 2018. Available online: https://www.iea.org/newsroom/news/2018/april/commentary-imo-agrees-to-first-long-term-plan-to-curb-shippingemissions.html (accessed on 10 March 2019). 3. Bengtsson, S.K.; Fridell, E.; Andersson, K.E. Fuels for short sea shipping: A comparative assessment with focus on environmental impact. J. Eng. Marit. Environ. 2015,228, 44–54. [CrossRef] 4. Kesieme, U.; Pazouki, K.; Murphy, A.; Chrysanthou, A. Biofuel as an alternative shipping fuel: Technological, environmental and economic assessment. Sustain. Energy Fuels 2019,3, 899–909. [CrossRef] 5. Kesieme, U.; Pazouki, K.; Murphy, A.; Chrysanthou, A. Attributional life cycle assessment of biofuels for shipping: Addressing alternative geographical locations and cultivation systems. J. Environ. Manag. 2019,235, 96–104. [CrossRef] [PubMed] 6. Acomi, N.; Acomi, O.C. Improving the Voyage Energy Efficiency by Using EEOI. Procedia-Soc. Behav. Sci. 2014 ,138, 531–536. [CrossRef] 7. Anˇci´c, I.; Šestan, A. Influence of the required EEDI reduction factor on the CO 2 emission from bulk carriers. Energy Policy 2015 , 84, 107–116. [CrossRef] 8. Johnson, H.; Johansson, M.; Andersson, K.; Södahl, B. Will the ship energy efficiency management plan reduce CO 2 emissions? A comparison with ISO 50001 and the ISM code. Marit. Policy Manag. 2013,40, 177–190. [CrossRef] 9. IMO. Resolution Mepc. 2011. Available online: https://www.imo.org/en/KnowledgeCentre/IndexofIMOResolutions/Pages/ MEPC-2010-11.aspx (accessed on 5 January 2022). 10. Gilbody, S.; Wilson, P.; Watt, I. Benefits and harms of direct to consumer advertising: A systematic review. Qual. Saf. Health Care 2005,14, 246–250. [CrossRef] 11. Periˇci´c, T.P.; Tanveer, S. Why Systematic Reviews Matter—A Brief History, Overview and Practical Guide for Authors. 2019. Available online: https://www.elsevier.com/connect/authors-update/why-systematic-reviews-matter (accessed on 12 December 2021). 12. Balcombe, P.; Brierley, J.; Lewis, C.; Skatvedt, L.; Speirs, J.; Hawkes, A.; Staffell, I. How to decarbonise international shipping: Options for fuels, technologies and policies. Energy Convers. Manag. 2019,182, 72–88. [CrossRef] 13. Noor, C.W.M.; Noor, M.M.; Mamat, R. Biodiesel as alternative fuel for marine diesel engine applications: A review. Renew. Sustain. Energy Rev. 2018,94, 127–142. [CrossRef] 14. Palocz-Andresen, M. Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation; Springer: Cham, Switzerland, 2012; ISBN 978-3-642-11976-7. 15. Statista. Installed Power Capacity in the European Union (EU-28) in 2005 and 2017, by Generation Type. 2020. Available online: https://www.statista.com/statistics/807675/installed-power-capacity-european-union-eu-28/ (accessed on 19 December 2021). 16. Maloni, M.; Paul, J.A.; Gligor, D.M. Slow steaming impacts on ocean carriers and shippers. Marit. Econ. Logist. 2013 ,15, 151–171. [CrossRef] 17. Zamiatina, N. Comparative Overview of Marine Fuel Quality on Diesel Engine Operation. Procedia Eng. 2016 ,134, 157–164. [CrossRef] 18. Bijleveld, T. From Lignin to Marine Biofuel; Universiteit Utrecht/GoodFuels: Utrecht, The Netherlands, 2016. 19. Vermiere, M.B. Everything You Need to Know About Marine Fuels. Ghent, Belgium. 2021. Available online: https://www. chevronmarineproducts.com/content/dam/chevron-marine/Brochures/Chevron_EverythingYouNeedToKnowAboutFuels_ v3_1a_DESKTOP.pdf (accessed on 2 March 2022).
Energies 2022,15, 3571 25 of 30 20. IMO. Third IMO Greenhouse Gas Study 2014. London—International Maritime Organization. 2014. Available online: https://www.imo.org/en/OurWork/Environment/Pages/Greenhouse-Gas-Studies-2014.aspx#:~{}:text=The%20Third%20 IMO%20GHG%20Study%202014%20used%20qualitative%20information%20from,evaluate%20global%20domestic%20fuel% 20consumption (accessed on 25 January 2022). 21. Olmer, N.; Comer, B.; Roy, B.; Mao, X.; Rutherford, D. Greenhouse Gas Emissions From Global Shipping, 2013–2015. The International Council on Clean Transportation—ICCT—Whashington—USA. 2017. Available online: https://www.theicct.org/ sites/default/files/publications/Global-shipping-GHG-emissions-2013-2015_ICCT-Report_17102017_vF.pdf (accessed on 29 January 2022). 22. Deniz, C.; Zincir, B. Environmental and economical assessment of alternative marine fuels. J. Clean. Prod. 2016 ,113, 438–449. [CrossRef] 23. Jiang, L.; Kronbak, J.; Pil, L. The costs and benefits of sulphur reduction measures: Sulphur scrubbers versus marine gas oil. ransp. Res. Part D Transp. Environ. 2014,28, 19–27. [CrossRef] 24. IMO. Adoption of the Initial IMO Strategy on Reduction of GHG Emissions from Ships and Existing IMO Activity Related to Reducing GHG Emissions in the Shipping Sector. London—International Maritime Organization, p. 27. 2018. Available online: https://unfccc.int/sites/default/files/resource/250_IMO%20submission_Talanoa%20Dialogue_April%202018.pdf (accessed on 11 February 2022). 25. Karl, M.; Bieser, J.; Geyer, B.; Matthias, V.; Jalkanen, J.-P.; Johansson, L.; Fridell, E. Impact of a nitrogen emission control area (NECA) on the future air quality and nitrogen deposition to seawater in the Baltic Sea region. Atmos. Chem. Phys. 2019 ,19, 1721–1752. [CrossRef] 26. Van, T.C.; Ramirez, J.; Rainey, T.; Ristovski, Z.; Brown, R.J. Global impacts of recent IMO regulations on marine fuel oil refining processes and ship emissions. Transp. Res. Part D Transp. Environ. 2019,70, 123–134. [CrossRef] 27. IRENA. A Pathway to Decarbonize the Shipping Sector. Abu Dhabi—United Arab Emirates. 2021. Available online: www.irena. org (accessed on 20 April 2022). 28. Bouman, E.A.; Lindstad, E.; Rialland, A.I.; Strømman, A.H. State-of-the-art technologies, measures, and potential for reducing GHG emissions from shipping—A review. Transp. Res. Part D Transp. Environ. 2017,52, 408–421. [CrossRef] 29. Psaraftis, H.N.; Kontovas, C.A. Balancing the economic and environmental performance of maritime transportation. Transp. Res. Part D Transp. Environ. 2010,15, 458–462. [CrossRef] 30. Web of Science. Web of Science. 2022. Available online: http://login.webofknowledge.com/error/Error?Error=IPError& PathInfo=%2F&RouterURL=http%3A%2F%2Fwww.webofknowledge.com%2F&Domain=.webofknowledge.com&Src=IP& Alias=WOK5 (accessed on 20 September 2020). 31. Ampah, J.D.; Yusuf, A.A.; Afrane, S.; Jin, C.; Liu, H. Reviewing two decades of cleaner alternative marine fuels: Towards IMO’s decarbonization of the maritime transport sector. J. Clean. Prod. 2021,320, 128871. [CrossRef] 32. Winnes, H.; Styhre, L.; Fridell, E. Reducing GHG emissions from ships in port areas. Res. Transp. Bus. Manag. 2015 ,17, 73–82. [CrossRef] 33. Gilbert, P.; Walsh, C.; Traut, M.; Kesieme, U.; Pazouki, K.; Murphy, A. Assessment of full life-cycle air emissions of alternative shipping fuels. J. Clean. Prod. 2020,172, 855–866. [CrossRef] 34. Styhre, L.; Winnes, H.; Black, J.; Lee, J.; Le-Griffin, H. Greenhouse gas emissions from ships in ports—Case studies in four continents. Transp. Res. Part D Transp. Environ. 2017,54, 212–224. [CrossRef] 35. Armstrong, V.N. Vessel optimisation for low carbon shipping. Ocean Eng. 2013,73, 195–207. [CrossRef] 36. Ghenai, C.; Bettayeb, M.; Brdjanin, B.; Hamid, A.K. Hybrid solar PV/PEM fuel Cell/Diesel Generator power system for cruise ship: A case study in Stockholm, Sweden. Case Stud. Therm. Eng. 2019,14, 100497. [CrossRef] 37. Hirdaris, S.; Cheng, Y.; Shallcross, P.; Bonafoux, J.; Carlson, D.; Prince, B.; Sarris, G. Considerations on the potential use of Nuclear Small Modular Reactor (SMR) technology for merchant marine propulsion. Ocean Eng. 2014,79, 101–130. [CrossRef] 38. Petzold, A.; Lauer, P.; Fritsche, U.; Hasselbach, J.; Lichtenstern, M.; Schlager, H.; Fleischer, F. Operation of marine diesel engines on biogenic fuels: Modification of emissions and resulting climate effects. Environ. Sci. Technol. 2011 ,45, 10394–10400. [CrossRef] 39. Righi, M.; Klinger, C.; Eyring, V.; Hendricks, J.; Lauer, A.; Petzold, A. Climate impact of biofuels in shipping: Global model studies of the aerosol indirect effect. Environ. Sci. Technol. 2011,45, 3519–3525. [CrossRef] 40. Bengtsson, S.; Andersson, K.; Fridell, E. A comparative life cycle assessment of marine fuels: Liquefied natural gas and three other fossil fuels. Proc. Inst. Mech. Eng. Part M J. Eng. Marit. Environ. 2011,225, 97–110. [CrossRef] 41. Elgohary, M.M.; Seddiek, I.S.; Salem, A.M. Overview of alternative fuels with emphasis on the potential of liquefied natural gas as future marine fuel. Proc. Inst. Mech. Eng. Part M J. Eng. Marit. Environ. 2015,229, 365–375. [CrossRef] 42. Bicer, Y.; Dincer, I. Environmental impact categories of hydrogen and ammonia driven transoceanic maritime vehicles: A comparative evaluation. Int. J. Hydrogen Energy 2018,43, 4583–4596. [CrossRef] 43. Müller-Casseres, E.; Carvalho, F.; Nogueira, T.; Fonte, C.; Império, M.; Poggio, M.; Wei, H.K.; Portugal-Pereira, J.; Rochedo, P.R.; Szklo, A.; et al. Production of alternative marine fuels in Brazil: An integrated assessment perspective. Energy 2021 ,219, 119444. [CrossRef] 44. Lin, C.Y. Effects of biodiesel blend on marine fuel characteristics for marine vessels. Energies 2013,6, 4945–4955. [CrossRef]