Introduction

The maritime industry is undergoing a historic transformation driven by regulatory pressure, stakeholder demands, and environmental urgency. With the International Maritime Organization (IMO) targeting a net-zero GHG emission target by 2050, traditional fossil-based bunker fuels are rapidly losing favor. Among the myriad of alternative marine fuels, ammonia and methanol have emerged as promising candidates due to their scalability, lower emissions profiles, and potential for renewable production.

This article presents a techno-economic analysis of ammonia and methanol as future bunker fuels, comparing their chemical properties, energy efficiency, infrastructure requirements, cost implications, engine compatibility, and lifecycle emissions.

1. Chemical and Physical Properties

Understanding the fundamental properties of ammonia (NH₃) and methanol (CH₃OH) is key to assessing their suitability as marine fuels.

Property	Ammonia	Methanol
Molecular Formula	NH₃	CH₃OH
Energy Density (LHV)	~18.6 MJ/kg	~20 MJ/kg
Density	682 kg/m³	792 kg/m³
Toxicity	High (toxic & corrosive)	Moderate
Flash Point	~132°C (non-flammable)	~11°C (flammable)
Carbon Content	Zero	Contains Carbon

• Ammonia has the advantage of being carbon-free, emitting no CO₂ during combustion, although it requires a high ignition temperature and presents toxicity and safety concerns.
• Methanol, though carbon-based, can be produced renewably and emits lower NOx and SOx compared to conventional marine fuels.

2. Engine Compatibility and Retrofits

Ammonia:

Ammonia is not yet widely used in marine engines, but several prototypes are under development:

• Dual-fuel ammonia engines are being designed by manufacturers such as MAN Energy Solutions and WinGD.
• Ammonia requires a pilot fuel or co-firing with hydrogen or diesel to ensure stable combustion.
• The fuel’s corrosive nature requires the use of special materials in engine components and fuel systems.

Methanol:

Methanol has seen earlier adoption in shipping:

• Retrofits are relatively straightforward, especially for four-stroke engines.
• Major companies like Maersk have committed to methanol-capable vessels.
• Scandlines and Stena Line are already operating methanol-fueled ships.

Verdict: Methanol currently has the upper hand in terms of commercial viability and operational maturity, though ammonia offers stronger long-term decarbonization potential.

3. Energy Efficiency and Storage Requirements

Both fuels have lower volumetric energy densities than traditional heavy fuel oil (HFO) or marine gas oil (MGO), which implies increased fuel storage needs.

Fuel Type	Volumetric Energy Density (MJ/L)	Relative Volume Needed (vs HFO)
HFO	~40	1.0
Methanol	~15.6	~2.5x
Ammonia	~12.7	~3x

• Ships using ammonia or methanol will require larger or additional fuel tanks, potentially reducing cargo space.
• Ammonia is stored either as a pressurized liquid (~10 bar) or a cryogenic liquid (~ -33°C), adding to complexity.
• Methanol is liquid at ambient conditions, making it easier to store and handle.

4. Fuel Production Pathways and Scalability

Methanol:

Methanol can be produced via:

• Fossil feedstocks (coal, natural gas)
• Biomass gasification
• Power-to-liquid (green methanol) using CO₂ and green hydrogen

Scalability: Green methanol production is growing, and several industrial-scale projects are under development. However, carbon sourcing for synthetic methanol poses a challenge.

Ammonia:

Ammonia production methods include:

• Grey ammonia: From fossil fuels (high emissions)
• Blue ammonia: Fossil-based with carbon capture
• Green ammonia: From water electrolysis and nitrogen fixation

Scalability: Green ammonia requires substantial renewable electricity, electrolyzers, and Haber-Bosch plant optimization. The challenge is achieving production at competitive costs.

5. Emissions Profile and Environmental Impact

Fuel	CO₂ Emissions	NOx Emissions	SOx & PM	GHG Reduction Potential
Ammonia	0	High*	None	Up to 100% (green)
Methanol	Low (or zero if green)	Low	Low	~80–100%

• Ammonia may generate nitrous oxide (N₂O), a potent GHG, during incomplete combustion—requiring advanced after-treatment systems.
• Methanol combustion is relatively clean and easier to manage using existing emissions control systems.

6. Safety and Regulatory Considerations

Both fuels pose unique safety and regulatory challenges:

Ammonia:

• Highly toxic via inhalation and corrosive to human tissue.
• Requires robust ventilation, leak detection, and crew training.
• IMO is currently working on safety guidelines through the IGF Code revisions.

Methanol:

• Flammable but less toxic.
• Already recognized under IMO’s IGF Code, with operational ships as reference cases.

7. Infrastructure and Bunkering Requirements

Methanol:

• Can be handled with existing liquid fuel infrastructure with minimal modifications.
• Terminals in Rotterdam, Singapore, and Scandinavia are expanding methanol bunkering capabilities.

Ammonia:

• Requires dedicated handling systems due to toxicity and storage temperature/pressure needs.
• Most global ports lack ammonia bunkering capability, though pilot projects are underway in Japan, Korea, and Australia.

8. Techno-Economic Viability

Parameter	Ammonia	Methanol
Fuel Cost (est. 2025)	$900–$1,200/ton (green)	$500–$800/ton (green)
Engine Retrofit Cost	High	Moderate
Infrastructure Investment	Very High	Low to Moderate
OPEX	High (due to safety)	Moderate

Methanol has a clear cost advantage in the near term, while ammonia may become more viable as production costs decrease through electrolyzer scale-up and green hydrogen supply chains.

9. Industry Adoption and Investment Trends

• Maersk has ordered over 20 methanol-fueled vessels and is investing in green methanol production partnerships.
• Yara International, MAN Energy Solutions, and others are heavily involved in ammonia fuel consortiums.
• Classification societies like DNV and Lloyd’s Register are developing technical guidelines for both fuels.

The trajectory indicates that methanol will dominate the 2020s, while ammonia could become mainstream post-2035, especially for long-haul deep-sea shipping.

Conclusion

The path to decarbonizing the maritime industry is complex and fuel choice plays a pivotal role. This techno-economic analysis reveals that:

• Methanol is a near-term, practical solution with mature infrastructure and lower retrofit costs.
• Ammonia, while challenging in terms of safety and technology readiness, offers a true zero-carbon pathway and greater long-term sustainability.

Ultimately, the decision between ammonia and methanol will depend on vessel type, route profile, investment horizon, and fuel availability. A multi-fuel future is likely, where shipowners strategically choose fuels based on operational needs and evolving regulations.