Sage Journals: Discover world-class research

Abstract

Marine fuels are the main sources of pollution from shipping industry. Hydrogen and ammonia have been suggested to be alternative fuels for shipping as these two fuels do not emit carbon dioxides in the combustion process. This study employed life cycle assessment method to compare the environmental performance of propulsion systems using hydrogen and ammonia as marine fuels to fossil fuels. 2-stroke and 4-stroke engines of tankers using fossil fuels were chosen as base case scenarios. Alternative scenarios using ‘green’ and ‘blue’ hydrogen and ammonia with the support of pilot fuel were then compared to the base case scenarios. While the performance of the coming combustion concepts for hydrogen and ammonia engines are still unknown, preliminary estimations were used in this study. The results showed that hydrogen and ammonia could substantially reduce the global warming potential, compared with the fossil fuel scenarios. Hydrogen and ammonia are also expected to be highly effective in cutting down the particulate matter and the emission of black carbon.

Keywords

LCA emissions environmental impacts hydrogen ammonia marine engine life cycle

Introduction

With the majority of cargo capacity transported by sea, marine transport plays an important role in international trade.¹ The pollution from shipping is gaining increasing attention, due to the huge amount of emissions exhausted from ship operation.^2–4 IMO regulated air pollution in Annexe VI of the MARPOL convention. For example, Chapter 3 regulations 13–15 limit NO_X, SO_X and VOCs from shipping.⁵ Chapter 4 regulations 19–28 address the greenhouse gas emissions from fuel use, with IMO Lifecycle GHG – carbon intensity guidelines currently under development, and expected to be agreed upon at MEPC 80 in 2023.

Shipping decarbonization is a critical part of meeting the Paris Agreement target: to meet global warming to 1.5°C and to build a zero-emissions planet.⁶ IMO’s ambitious GHG target is to reduce the CO₂ emissions per transportation work from the shipping industry by 40% by 2030 and 70% by 2050, in comparison to 2008. The vision and ambitions of IMO within this century is to achieve zero-emissions goal.⁷ The initial IMO strategy is divided into three periods: short-term 2018–2023, mid-term 2023–2030 and long-term 2030–2100. Considering that the life span of cargo vessels is 25–30 years, the present is the right time to find new emission reduction mechanisms for the shipping industry to achieve the ambitious target. Marine fuels are crucial actors and have important roles in IMO’s strategy.

Nowadays, the huge amount of fossil fuels, for example, HFO, MDO, LNG, etc. used in the shipping industry is the main contributor to greenhouse gas emissions to the atmosphere. Some new solutions are suggested to lighten the impacts from shipping on the environment. These include alternative fuels (H₂, NH₃, methanol, etc.), hybrid propulsion systems, carbon capture and storage techniques, renewable energy (from wind, solar or wave).^8–11 The benefits of these solutions need to be further discussed as each solution has both advantages as well as limitations. Among the alternative fuels in shipping, NH₃ and H₂ seem to be competitive candidates as the combustion of these fuels does not emit the carbon emissions.¹² However, from a life cycle perspective, the upstream process (production phase) of these fuels needs careful consideration.

H₂ is the most common chemical element and it is a promising option for green energy in the future.¹³ The main product from H₂ combustion is water, though depending on the process used, by-product of this process are NO_X and the release of unburned H₂. Currently, the majority of H₂ is also produced by using the steam-methane reforming method with/without CCS technology.¹⁴ H₂ is also produced by using the water separation technique (electrolysis) using electricity and water. Even though renewable energy such as solar and wind energy can be used, H₂ production still has impacts on the environment due to the need for land, material consumption in infrastructure, and the need for large investments. Another barrier of using H₂ as a marine fuel is the storage of H₂ on board. The space required for H₂ storage is larger than the other fuels such as LNG, NH₃ and MDO.¹⁵ If H₂ is stored in liquid form at very low temperature (−253°C) it either has a limited lifetime before the evaporation, or it requires additional energy for keeping in liquid form.¹⁶ H₂ can be stored in pressurized form, but has then a limited energy density (5.15 GJ/m³ at 800 bar), compared to 8.55 GJ/m³ in liquid form.¹⁷ Given the higher energy density, liquid hydrogen was assumed to be the most appropriate form of bunkering for long-distance shipping in this work.

H₂ and NH₃ are often categorized using a taxonomy of different colour codes. ‘Grey’ H₂ is produced from natural gas or coal by using steam-methane reforming or gasification processes. If carbon emissions from these processes are captured, the product will be ‘blue’ H₂. The carbon capture rate by when producing ‘blue’ H₂ is normally from 85 to 95%.¹⁸‘Green’ H₂ is produced by using electrolysis to separate H₂ and oxygen from water using electricity from renewable sources (e.g. wind, solar, wave energy, etc.). Nowadays, the usage of ‘green’ H₂ is still limited.¹⁹

NH₃ is produced by using a chemical synthesis technique, the Haber-Bosch process (Figure 1). The taxonomy of colour codes for NH₃ depends on the type of H₂ used in the synthesis process. Compared with H₂, NH₃ requires less space for on-board energy storage. Moreover, NH₃ is also considered as a balanced solution with high volumetric energy and more practical storage characteristics (Table 1).

Figure 1.

NH₃ and H₂ production processes.

Table 1.

Comparison of fuel properties.¹⁵

Fuel type	Energy content [MJ/kg]	Volumetric energy density [GJ/m3]	Storage pressure [bar]	Storage temperature [°C]
Marine Gas Oil	42.7	36.6	1	20
Liquid Methane	50.0	23.4	1	−162
Ethanol	26.7	21.1	1	20
Methanol	19.9	15.8	1	20
Liquid NH₃	18.6	12.7	1 or 10	−34 or 20
Liquid H₂	120.0	8.5	1	−253
Compressed H₂	120.0	7.5	700	20

The LCA is considered a comprehensive method to evaluate the environmental performance of a product or service.²⁰ This method has been applied in maritime industry recently. Bengtsson et al.²¹ compared the LCA of LNG and the fossil fuels and indicated the need of LCA when estimating the environmental impacts of marine fuels. The LCA of alternative fuels were studied in.^5,22,23 Recently, under the HyMethShip concept, the LCA method was also used to evaluate the environmental the performance of propulsion systems using onboard carbon capture technique.^24,25 The framework of LCA of marine engines was established^26,27 then were used to investigate the life cycle performance of a tugboat.²⁸ The reader should refer to a comprehensive review²⁹ for the application of LCA in maritime sector.

Some research papers also studied the environmental impacts of H₂ and NH₃. For instance, the comparison of blue H₂ and fossil fuel was presented by Howarth et al.,¹⁴ showing that the use of blue H₂ may lead to higher environmental impacts than fossil fuel. Perčić et al.³⁰ also indicated that the fuel cell system could reduce up to 84% of greenhouse gases when green NH₃ is used. Bicer et al.³¹ discussed the possibility of using H₂ in shipping transportation from a life cycle perspective. Hwang et al.³² compared the LCA of natural gas and marine gas oil for the ship operating in Korea.

By using LCA and life-cycle cost assessment, Perčić et al.^33,34 and Fan et al.³⁵ showed that a battery-powered vessel has lower environmental footprint and low cost than a diesel engine-powered vessel. For fishing trawlers, Koričan et al.³⁶ indicated that soybean–biodiesel–diesel blend and LNG could reduce greenhouse gases and have positive impact on the life cycle cost.

To clarify the benefit of H₂ and NH₃ in shipping industry, this study employed the LCA method to investigate the environmental impacts of marine engines using H₂ and NH₃ as marine fuels (comprising both ‘blue’ and ‘green’ H₂ and NH₃). The results were compared to the environmental impacts of marine engines using fossil fuels.

The study is structured as follows. After the introductory part, the LCA method applied in this study is presented in Sections 2 and 3. Results and discussion are presented in Section 4 with the conclusions of this work drawn in Section 5.

Life cycle assessment

This study is a comparative attributional LCA study and impact assessment, based on the IPCC and CML2001 impact assessment methods. Five environmental indicators such as GWP100, GWP20, AP, EP, POCP were calculated as these indicators are mostly concerned by maritime industry regulations.³⁷ Calculations and results were obtained from LCA for Experts (GaBi) software application and database. Procedure to obtain the results from are following.

(1) Finding the necessary processes/flows for the life cycle of the marine from the database (ecoinvent, Sphera).

(2) Connecting processes to establish life cycle model.

(3) Running model. GaBi has tools and many useful functions (including sensitivity analysis) which helps LCA practitioners to get results easily.

Goal definition

As presented above, the reason for carrying out this study is to compare the environmental impacts of H₂ and NH₃ with the usage of fossil fuels. The applications are to provide information to the research community and assist decision-making process in selecting the alternative fuels for decarbonization purpose. Maritime stakeholders, naval architects, ship-owners, policy makers, and the public are the intended audience of the study.

Figure 2 illustrates the diagram of system boundary and life cycle phases of marine engines. The life cycle of marine engine consists of the phases of material and fuel production, the operation and maintenance phase, production phase and end-of-life phase. In this study, the maintenance activities and human factor are ignored in order to simplify. The inputs and outputs of the life cycle are energy, materials, and emissions flows.

Figure 2.

Life cycle phases of a marine engine.

Functional unit definition

The investigated product in this study is a main engine of ship, of which, the main function is to create energy in combustion process to propulsive the ship. The functional unit chosen is 1 kW hour (1 kWh) delivered to the propeller shaft. The results will be presented per one kWh, for example, kilogram of CO₂ eq./kWh.

Eight scenarios

In this study, eight scenarios with different marine fuels and engines were investigated (Table 2). 2S_fossil and 4S_fossil scenarios were chosen as the base case scenarios with 100% of fossil fuels used on ship. The scenarios and the fuel consumption of the ships were based on the real ship operation using chemical tankers (Stolt Tankers B.V.). Some difference exists in the size and age of the vessels and engines, given practical limitations of data and variations in vessel and engine size in the fleet. The 4-stroke powered ship consisted of a 37,059 DWT Chemical & Oil Carrier built in 2001 using a 9-cylinder 4-stroke engine with 320 mm bore and 350 mm stroke. It had a maximum continuous power rating of 10,944 kW. In the H₂ scenarios, H₂ (only in 4-stroke engines) were used as main fuel with 1.5% MDO necessary (percentage fraction given by energy content) as pilot injection along the balance of H₂ main fuel (98.5%). NH₃ scenarios used 88% NH₃ as main fuel. The two-stroke engine ship consisted of a 33,723 DWT Chemical & Oil Carrier, built in 2017 using a 5-cylinder engine with 500 mm bore, 2500 mm stroke, and a maximum continuous power rating of 5850 kW. The fraction of pilot fuel injection was assumed to be 5% MDO with 95% NH₃ as main fuel.

Table 2.

Scenarios in this study.

Scenarios	Items	Unit	HFO/MDO	NH₃	H₂
2S_fossil	Energy contribution	-	100%	0%	0%
	Energy	kWh	1	0	0
	Mass	g	180.2	0	0
2S_GNH₃ 2S_BNH₃	Energy contribution	-	5%	95%	0%
	Energy	kWh	0.05	0.95	0
	Mass	g	9.01	392.08	0
4S_fossil	Energy contribution	-	100%	0%	0%
	Energy	kWh	1	0	0
	Mass	g	219.3	0	0
4S_GH₂ 4S_BH₂	Energy contribution	-	1.5%	0%	98.5%
	Energy	kWh	0.015	0	0.985
	Mass	g	3.3	0	76.7
4S_GNH₃ 4S_BNH₃	Energy contribution	-	12%	88%	0%
	Energy	kWh	0.12	0.88	0
	Mass	g	26.3	44.2	0

The fossil fuel and NH₃ scenarios were updated with the inclusion of SCR technologies in order to meet the requirements in the NO_X emission limits of Regulation 13 of MARPOL Annexe VI. The estimation will be 15 g of urea per 1 kWh could reduce 90% NO_X.³⁸ The application of SCR affected the results of NO_X emissions as well as the GWP in the LCA of marine engines. Since the interest towards NH₃ and H₂ as competitive candidates to reduce carbon emissions from shipping only gain larger attention in recent years, there are not yet consistent emission data available. Within the coming years new insight to the emission levels from NH₃ and H₂ with different engine technologies will very likely be published.

Assumptions and limitations

Assumptions and limitations are inevitable in LCA studies due to the numerous datasets and information in the product’s life cycle. In this study, assumptions and limitations are listed as below:

Only steel was considered as the material used to produce the vessels’ main engines, the secondary materials such as copper, aluminium, etc. were ignored.

The transportation mode used for transporting fuel from fuel production site (Porsgrunn, Norway) to the port (Port of Amsterdam, the Netherlands) was ocean-going vessels with the distance of 800 km.

The vessels and main engines will be retired and dismantled after 25 years operating at sea. In this study, end-of-life of the engine is considered.

Waste management and generation during the engine’s life cycle were not considered.

Primary emissions

Most emissions from the shipping industry are released as exhaust gases and these emissions have impacts on the environment, leading to effects on the climate, human health and the marine environment among other. Since emissions to air are the most important emissions the foreground system is limited to the emissions to air. The list of primary emissions includes CO₂, PM, CH₄, NO_X and N₂O. Most of these emissions were investigated in the GHG report of the IMO.³⁹

Sensitivity analysis description

In order to validate the robustness of the results, sensitivity analyses were preformed (Table 3). First, the rate of MDO used for pilot injection process was analysed for the H₂ and NH₃ scenarios. Second, the percentage of H₂ boil-off, which depends on the length of vessel’s voyages and the boil-off H₂ rate (from 0.1% to 1% per day), was considered.⁴⁰ In the initial stage, 0.5% boil-off H₂ per day was used. The H₂ boil-off can lead to the extra fuel consumption due to the increase of energy used for re-liquefaction. Third, CO₂ capture rate in CCS technology (from 85% to 95%) and the energy demand for H₂ liquefaction (from 6 to 10 kWh/kgH₂)⁴¹ were also taken into account in the sensitivity analysis. Moreover, the N₂O emission factor in engine combustion were considered in this part.

Table 3.

Sensitivity analysis description.

Scenarios	Sensitivity analysis (SA)
	Emission factors of N₂O in engine combustion		MDO for pilot injection (%)		Rate of H₂ boil-off (%)		Energy for H₂ liquefaction (kWh/kgH₂)
	Upper limit	Lower limit	Upper limit	Lower limit	Upper limit	Lower limit	Upper limit	Lower limit
2S_fossil	-	-	-	-	-	-	-	-
2S_GNH₃ 2S_BNH₃	10 times higher	50% of base case	10.0%	2.5%	-	-	-	-
4S_fossil	-	-	-	-	-	-	-	-
4S_GH₂ 4S_BH₂	-	-	3%	0%	1%	0.10%	10	6
4S_GNH₃ 4S_BNH₃	10 times higher	50% of base case	18%	6%	-	-	-	-

Life cycle inventory

The life cycle inventory consists of the mass, energy and emission information for all inputs and outputs of life cycle system for the fossil fuels, H₂ and NH₃ engines. The data for this part were provided by GaBi software and data providers. Data were also collected and gathered from literature such as publications, technical reports, etc.

Fuel production and transportation

Fuel production database is available in GaBi software and database. After production phase, fossil fuels was transported by ocean-going vessels with the distance of 800 km to the refuelling station. H₂ and NH₃ were assumed to be produced in Porsgrunn, Norway. These two types of fuels were assumed to be transported by sea going vessel with the same distance with fossil fuels to the refuelling station.

In this work, the production of ‘green’ H₂ used the electricity from wind energy in Norway. In order to produce 1 kg of gaseous H₂ by electrolysis method, 192 MJ of electricity are consumed. After that, 36 MJ of electricity were assumed to be used for H₂ liquefaction process (1 kg H₂).⁴²

Steam reforming methane (or natural gas) is used to produce blue H₂. The carbon capture and storage in this process consumes 42.1 MJ/1 kg of H₂.⁴³ In this study, we assumed that 90% of carbon dioxide are captured in the H₂ production.

‘Blue’ H₂ was assumed to be used to produce ‘blue’ NH₃ by applying Haber-Bosch process. 0.824 kg of nitrogen from air separation, 0.176 kg of H₂ and 1.17 MJ of electricity⁴⁴ are consumed in order to produce 1 kg of NH₃.⁴⁵ The liquefaction process of NH₃ consumes less electricity than H₂, only 3.01 MJ/kg NH₃ (estimated by the authors).

The final production step in the production of ‘green’ NH₃ is similar to that of ‘blue’ NH₃. The ‘green’ H₂ and energy are used with the same assumption as ‘blue’ NH₃ production for the Haber-Bosch synthesis step.

Fuel combustion and ship operation

The fuel consumption was obtained from operational data for the year 2021 (Table 4). The average fuel consumption over 1 year was 180.2 g/kWh for the two-stroke engine case, and 219 g/kWh for the 4-stroke engine case, based on the vessel data.

Table 4.

Fuel consumption of vessels in 2021 from noon report.

Engines	2-stroke engine vessel	4-stroke engine vessel
Average speed	14.5 knot	16.2 knot
Main engine power	5850 kW	10,944 kW
Auxiliary engines power	940 kW × 3	2430 kW × 2
Total fuel consumption	5054.5 ton HFO 758.8 ton MDO	5981.9 ton HFO 1648 ton MDO

Emission factors in ship operation are gathered from IMO’s GHG report³⁹ and estimated from some publications (Table 5). As H₂ and NH₃ are carbon-free fuels, using H₂ and NH₃ in this phase does not emit CO₂, CH₄, black carbon, and CO. In addition, using H₂ and NH₃ can eliminate PM₁₀, PM_2.5, SO_X and NMVOC emissions. However, a small amount of N₂O and NO_X is still generated due to the combustion of NH₃ and nitrogen. There are also some un-burned H₂ and NH₃ emitted to the air in this phase. However, the data for tank-to-wake for H₂ and NH₃ are very limited and it can be different. This will be considered in the sensitivity analysis of this study.

Table 5.

Emission factors in fuel combustion process (kg emission/kg fuel).

Emissions	MDO³⁹	HFO³⁴	H₂	NH₃
CO₂	3.20600	3.114	0.00000	0.00000
CH₄	0.00001	0.00005	0.00000	0.00000
N₂O	0.00018	0.0759	0.00000	0.00033⁴⁶
NO_X	0.05671	0.00018	0.02333⁴⁷	0.02033⁴⁸
CO	0.00259	0.00288	0.00000	0.00000
NMVOC	0.00240	0.0032	0.00000	0.00000
SO_X	0.00137	9.7752E-06	0.00000	0.00000
PM10	0.00090	0.00755	0.00000	0.00000
PM2.5	0.00083	0.00694	0.00000	0.00000
Black carbon (soot)	0.00038	0.00026	0.00000	0.00000
H₂ (unburned)	0.00000	0.00000	0.00800⁴⁹ *	0.00000
NH₃ (unburned)	0.00000	0.00000	0.00000	0.00950⁴⁸

Assumed 0.2% unburned fuel.

Material used in engine production

The cradle-to-grave life cycle of material was considered in this study. It included mainly the raw material extraction and production. After 25 years of operation, the engine will be scrapped and used for recycling.

As the chosen functional unit is one kWh delivered to the propeller shaft, the amount of material considered per each functional unit is defined by dividing the mass of engine by the total energy produced in the engine’s life cycle (kg of steel per kWh). The secondary material such as aluminium, copper, etc. were excluded due to the small amount, compared to the mass of steel.

Results and discussion

Life cycle emissions

Figure 3 presents the contribution of life cycle phases to the total mass of CO₂ in the life cycle of marine engine per unit of energy of shaft power delivered. Generally, CO₂ emissions could be effectively reduced by using H₂ and NH₃ solutions, compared to fossil fuels scenario. However, for ‘blue’ H₂ and ‘blue’ NH₃, CO₂ emissions from production phase (WTT) are much higher than for the WTT phase of fossil fuels.

Figure 3.

Life-cycle CO₂ emissions.

The CH₄ emissions are emitted mostly from the production phase (Figure 4). It should be noted that, due to the use of grid-electricity in the production phase, the amount of these emissions for ‘blue’ solutions are much higher than the ‘green’ ones, even higher than the amount of CH₄ in fossil fuel production phase.

Figure 4.

Life-cycle CH₄ emissions.

Figure 5 illustrates PM emissions from marine engine’s life cycle. The use phase of fossil fuels emit the higher amount of PM than H₂ and NH₃ scenarios. Meanwhile, the H₂ and NH₃ scenarios could reduce effectively these emissions. Regarding black carbon, fossil fuel scenario also generated much more amount of these emissions.

Figure 5.

Life cycle PM emissions.

The application of NH₃ in ship operation could increase the amount of N₂O emissions (Figure 6). NH₃ can only reduce a small amount of NO_X (Figure 7) and SCR needs to be used in the scenarios of fossil fuels and NH₃.

Figure 6.

Life-cycle N₂O emissions.

Figure 7.

Life cycle NO_X emissions.

Environmental indicators

Figure 8 illustrates the GWP of eight investigated scenarios in this study. It is clear that fossil fuel scenarios have higher GWP value than H₂ and NH₃ solutions. More than 50% of GWP could be reduced by using green H₂ or NH₃ as marine fuels (Table 6). When using fossil fuels, most of GHG emissions are emitted from the tank-to-wake phase, meanwhile, the GHG emissions of H₂ and NH₃ depend on the production phases. For 4S_GNH3 and 4S_BNH3, the use of fossil fuels considerably increase the amount GWP.

Figure 8.

GWP results.

Table 6.

GWP comparison between eight scenarios (unit: kg CO₂ eq./kWh).

Scenarios	GWP100	Comparisons (%)	GWP20	Comparisons (%)
2S_fossil	0.647	100.00	0.684	100.00
2S_GNH3	0.112	17.31	0.119	17.40
2S_BNH3	0.403	62.29	0.495	72.37
4S_fossil	0.786	100.00	0.832	100.00
4S_GNH3	0.182	23.16	0.194	23.32
4S_BNH3	0.511	65.01	0.617	74.16
4S_GH2	0.055	7.00	0.059	7.09
4S_BH2	0.407	51.78	0.512	61.54

Table 7 summarizes the environmental indicators results. Although the use of NH₃ as marine fuel could reduce the impact on climate change, it still has higher AP and EP values than fossil fuel scenarios.

Table 7.

Environmental indicators.

Units: GWP100 (kg CO₂ eq./kWh), GWP20 (kg CO₂ eq./kWh), AP (kg SOX eq./kWh), EP (kg phosphate eq./kWh), ODP (kg R11 eq./kWh), POCP (kg ethene eq./kWh).

Sensitivity analysis and black carbon

Figure 9 shows the sensitivity analysis of the GWP results. It can be seen that the most influential factor on the GWP results is N₂O emission factor for NH₃ scenarios. The upper N₂O emission factor can lead to 70.1% increase in GWP100 in 4S_BNH3 scenario, which is higher than GWP100 of 4S_fossil scenario. Therefore, blue NH₃ should be carefully considered when using as maritime fuel and the N₂O emission factor is needed to be investigated to support the decision-making process. The results for NH₃ scenarios are also greatly affected by the rate of pilot fuel, for example, 10% increase in rate of MDO leads to 23.1% increase in GWP20 value for 4S_GNH3 scenario. The green H₂ and NH₃ still show the lower value of GWP than fossil fuel scenarios.

Figure 9.

Sensitivity analysis of GWP results.

In case the characterization factors of black carbon for GWP100 and GWP20 are 1647.5 and 4470⁵⁰ respectively, the contribution of black carbon to the GWP results can be seen in Figure 10. The use of fossil fuels clearly bring the considerable impact of black carbon to GWP, especially to GWP20. Therefore, fossil fuel should be cut down in order to achieve the IMO’s decarbonization goals in 2030 and 2050. The rate and type of pilot fuel should be also considered and it depends on engine technologies in the future.

Figure 10.

Black carbon effect.

The advantage of using H₂ fuel is the lower GWP value, compared with NH₃. H₂ fuel also cuts down the amount of black carbon due to the small percentage of fossil fuels used in engines as pilot fuel. However, H₂ fuel is now limited used in 4-stroke engine. The use of H₂ on the ships that have long voyage should be carefully considered because of the boil-off rate of H₂. These ships require considerable amount of energy to keep H₂ on board and it could lead to the increase of GWP value of marine engines in the life cycle perspective.

Conclusions

The LCA methodology has been applied in this work in order to investigate the environmental performance of marine engines associated with eight scenarios using fossil fuels, ‘blue’ and ‘green’ H₂ and NH₃. In the LCA, the production of engine, fuel (well-to-tank), the usage phase (tank-to-wake) and the engine’s end-of-life were examined.

The initial results show that NH₃ and H₂ solutions could reduce the environmental impacts, in comparison with fossil fuels. The ‘green’ fuels are more environmentally friendly than the ‘blue’ ones. However, it should be noted that, the production of NH₃ and H₂ phases dominate the life cycle results. Different fuel production regions will bring different results in environmental performance of marine engines.

Due to the boil-off of H₂ in the storage H₂ on-board, penalty energy is required for the re-liquefaction process. Therefore, it seems that H₂ fuel does not show its advantages for the longer voyage. The space used for H₂ storage is also higher than NH₃ case. Generally, H₂ solution has less impact on the environment than the NH₃ solution in the system boundary of our work.

The limitation of this study is that it does not consider economic and social aspects of hydrogen/ammonia engines. The results of this study represent the current state-of-the-art technology, and future technologies might bring further improvements in not only environmental aspects but also societal and economic performance.

To meet IMO’s ambitious GHG targets, it is clear that green NH₃ and H₂ are potential candidates for cutting down the emissions from the shipping industry. However, some significant issues that are required attention such as fuel infrastructure, marine fuel logistics, cost benefits, safety aspects, etc. This ensures the advantages of alternative marine fuel application towards the sustainable shipping industry in the future.

Footnotes

Appendix

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work has received funding from the CAHEMA (Concepts of Ammonia and Hydrogen Engines for Marine Applications) project (application ID: 106982) funded by the Swedish Transport Administration (Trafikverket), Business Finland and The Research Council of Norway, as part of the Nordic Maritime Transport and Energy Research Programme.

ORCID iDs

Duc Tuan Dong

Alessandro Schönborn

Anastasia Christodoulou

References

Sirimanne

Hoffman

Juan

, et al. Review of maritime transport 2019. In: United Nations conference on trade and development, Geneva, Switzerland, 2019.

Smith

o’Keeffe

Aldous

, et al. Third IMO greenhouse gas study 2014. London: The International Maritime Organization, 2015.

Cullinane

. Atmospheric emissions from shipping: the need for regulation and approaches to compliance. Transp Rev 2013; 33: 377–401.

Corbett

Winebrake

Green

, et al. Mortality from ship emissions: a global assessment. Environ Sci Technol 2007; 41: 8512–8518.

Hua

Chen

. Alternative fuel for sustainable shipping across the Taiwan Strait. Transp Res D Transp Environ 2017; 52: 254–276.

UNFCCC. A Climate-Smart, Sustainable and Resilient Maritime Sector, https://climatechampions.unfccc.int/wp-content/uploads/2022/11/Joint-Statement-FINAL.pdf (2020, accessed 30 August 2022).

IMO. Initial IMO GHG Strategy, https://www.imo.org/en/MediaCentre/HotTopics/Pages/Reducing-greenhouse-gas-emissions-from-ships.aspx (2018, accessed 30 August 2022).

Wang

Wright

. A comparative review of alternative fuels for the maritime sector: economic, technology, and policy challenges for clean energy implementation. World 2021; 2: 456–481.

Zincir

Deniz

, et al. Methanol as a fuel for marine diesel engines. In: Shukla PC, Belgiorno G and Di Blasio G (eds) Alcohol as an alternative fuel for internal combustion engines. Singapore: Springer, 2021, pp.45–85.

10.

Shukla

Belgiorno

Di Blasio

, et al. Alcohol as an alternative fuel for internal combustion engines. Singapore: Springer, 2021.

11.

Wang

Zhou

Liu

. Theoretical investigation of the combustion performance of ammonia/hydrogen mixtures on a marine diesel engine. Int J Hydrogen Energy 2021; 46: 14805–14812.

12.

Lindstad

Lagemann

Rialland

, et al. Reduction of maritime GHG emissions and the potential role of E-fuels. Transp Res D Transp Environ 2021; 101: 1–15. DOI: 10.1016/j.trd.2021.103075

13.

Nikolaidis

Poullikkas

. A comparative overview of hydrogen production processes. Renew Sustain Energ Rev 2017; 67: 597–611.

14.

Howarth

Jacobson

. How green is blue hydrogen? Energy Sci Eng 2021; 9: 1676–1687.

15.

Vries

. Safe and effective application of ammonia as a marine fuel, 2020.

16.

Aziz

. Liquid hydrogen: A review on liquefaction, storage, transportation, and safety. Energies 2021; 14: 5917.

17.

IEA. The Future of Hydrogen - Seizing today’s opportunities, 2019.

18.

IRENA. Green Hydrogen: A guide to policy making, 2020.

19.

Al-Enazi

Okonkwo

Bicer

, et al. A review of cleaner alternative fuels for maritime transportation. Energy Rep 2021; 7: 1962–1985.

20.

Finkbeiner

. The international standards as the constitution of life cycle assessment: the ISO 14040 series and its offspring. In: Background and future prospects in life cycle assessment. Springer, 2014, pp.85–106.

21.

Bengtsson

Andersson

Fridell

. A comparative life cycle assessment of marine fuels. Proc IMechE, Part M: J Engineering for the Maritime Environment 2011; 225: 97–110.

22.

Perčić

Vladimir

Fan

. Techno-economic assessment of alternative marine fuels for inland shipping in Croatia. Renew Sustain Energ Rev 2021; 148: 111363.

23.

Bilgili

. Comparative assessment of alternative marine fuels in life cycle perspective. Renew Sustain Energ Rev 2021; 144: 110985.

24.

Malmgren

Brynolf

Fridell

, et al. The environmental performance of a fossil-free ship propulsion system with onboard carbon capture – a life cycle assessment of the HyMethShip concept. Sustain Energy Fuels 2021; 5: 2753–2770.

25.

Kanchiralla

Brynolf

Malmgren

, et al. Life-cycle assessment and costing of fuels and propulsion systems in future fossil-free shipping. Environ Sci Technol 2022; 56: 12517–12531.

26.

Ling-Chin

Heidrich

Roskilly

. Life cycle assessment (LCA) – from analysing methodology development to introducing an LCA framework for marine photovoltaic (PV) systems. Renew Sustain Energ Rev 2016; 59: 352–378.

27.

Ling-Chin

Roskilly

. Investigating the implications of a new-build hybrid power system for Roll-on/Roll-off cargo ships from a sustainability perspective – A life cycle assessment case study. Appl Energy 2016; 181: 416–434.

28.

Wang

Zhou

Liang

, et al. Optimization of tugboat propulsion system configurations: A holistic life cycle assessment case study. J Clean Prod 2020; 259: 120903.

29.

Mio

Fermeglia

Favi

. A critical review and normalization of the life cycle assessment outcomes in the naval sector. Articles description. J Clean Prod 2022; 370: 1–22. DOI: 10.1016/j.jclepro.2022.133476

30.

Perčić

Vladimir

Jovanović

, et al. Application of fuel cells with zero-carbon fuels in short-sea shipping. Appl Energy 2022; 309: 1–19. DOI: 10.1016/j.apenergy.2021.118463

31.

Bicer

Dincer

. Clean fuel options with hydrogen for sea transportation: a life cycle approach. Int J Hydrogen Energy 2018; 43: 1179–1193.

32.

Hwang

Gil

Lee

, et al. Life cycle assessment of alternative ship fuels for coastal ferry operating in Republic of Korea. J Mar Sci Eng 2020; 8: 660.

33.

Perčić

Ančić

Vladimir

. Life-cycle cost assessments of different power system configurations to reduce the carbon footprint in the Croatian short-sea shipping sector. Renew Sustain Energ Rev 2020; 131: 1–12. DOI: 10.1016/j.rser.2020.110028

34.

Perčić

Vladimir

Fan

. Life-cycle cost assessment of alternative marine fuels to reduce the carbon footprint in short-sea shipping: A case study of Croatia. Appl Energy 2020; 279: 115848.

35.

Fan

Wang

, et al. Decarbonising inland ship power system: Alternative solution and assessment method. Energy 2021; 226: 1–16. DOI: 10.1016/j.energy.2021.120266

36.

Koričan

Perčić

Vladimir

, et al. Alternative power options for improvement of the environmental friendliness of fishing trawlers. J Mar Sci Eng 2022; 10: 1882.

37.

Jeong

Jang

Lee

, et al. Is electric battery propulsion for ships truly the lifecycle energy solution for marine environmental protection as a whole? J Clean Prod 2022; 355: 1–21. DOI: 10.1016/j.jclepro.2022.131756

38.

Andersson

Winnes

. Environmental trade-offs in nitrogen oxide removal from ship engine exhausts. Proc IMechE, Part M: J Engineering for the Maritime Environment 2011; 225: 33–42.

39.

IMO. Fourth IMO GHG Study 2020, 2020.

40.

Wijayanta

Oda

Purnomo

, et al. Liquid hydrogen, methylcyclohexane, and ammonia as potential hydrogen storage: Comparison review. Int J Hydrogen Energy 2019; 44: 15026–15044.

41.

Andersson

Grönkvist

. Large-scale storage of hydrogen. Int J Hydrogen Energy 2019; 44: 11901–11919.

42.

Chatterjee

Parsapur

Huang

K-W

. Limitations of ammonia as a hydrogen energy carrier for the transportation sector. ACS Energy Lett 2021; 6: 4390–4394.

43.

Preuster

Alekseev

Wasserscheid

. Hydrogen storage technologies for future energy systems. Annu Rev Chem Biomol Eng 2017; 8: 445–471.

44.

Liu

Elgowainy

Wang

. Life cycle energy use and greenhouse gas emissions of ammonia production from renewable resources and industrial by-products. Green Chem 2020; 22: 5751–5761.

45.

Ghavam

Vahdati

Wilson

IAG

, et al. Sustainable ammonia production processes. Front Energy Res 2021; 9: 1–19. DOI: 10.3389/fenrg.2021.580808

46.

Westlye

Ivarsson

Schramm

. Experimental investigation of nitrogen based emissions from an ammonia fueled SI-engine. Fuel 2013; 111: 239–247.

47.

Tsujimura

Suzuki

. Development of a large-sized direct injection hydrogen engine for a stationary power generator. Int J Hydrogen Energy 2019; 44: 11355–11369.

48.

Theotokatos

Zhang

, et al. Numerical investigation of the high pressure selective catalytic reduction system impact on marine two-stroke diesel engines. Int J Nav Archit Ocean Eng 2021; 13: 659–673.

49.

Park

Nguyen

, et al. Investigation on the operable range and idle condition of hydrogen-fueled spark ignition engine for unmanned aerial vehicle (UAV). Energy 2021; 237: 1–9. DOI: 10.1016/j.energy.2021.121645

50.

EPA. Report to congress on black carbon, 2010.

Life cycle assessment of ammonia/hydrogen-driven marine propulsion

Abstract

Keywords

Introduction

Life cycle assessment

Goal definition

Functional unit definition

Eight scenarios

Assumptions and limitations

Primary emissions

Sensitivity analysis description

Life cycle inventory

Fuel production and transportation

Fuel combustion and ship operation

Material used in engine production

Results and discussion

Life cycle emissions

Environmental indicators

Sensitivity analysis and black carbon

Conclusions

Footnotes

Appendix

Declaration of conflicting interests

Funding

ORCID iDs

References