Retrofitting Marine Internal Combustion (IC) Engines for Methanol Fuel Integration

Abstract

The maritime sector is undergoing a significant transformation as it seeks to meet increasingly stringent environmental regulations imposed by international bodies such as the International Maritime Organization (IMO). Among the various alternative fuels being explored, methanol has emerged as a strong candidate due to its low emissions, ease of storage, and potential for carbon neutrality when produced from renewable sources. This paper investigates the feasibility and methodology of retrofitting conventional marine internal combustion (IC) engines for methanol usage, providing a comprehensive analysis of both low-pressure and high-pressure methanol fuel supply systems. The study delves into the working principles, components, advantages, and disadvantages of these systems, focusing on performance, safety, cost, and environmental impact. Furthermore, it examines dual-fuel strategies involving methanol and pilot diesel, particularly in the context of single-point injection (SPI) and multi-point injection (MPI) systems. The retrofitting process is explored in detail, including engine design modifications, injector configurations, and combustion behaviour with methanol\'s distinct physical and chemical properties. Comparative evaluations are provided to highlight the trade-offs between simpler low-pressure systems and more efficient but complex high-pressure configurations. Emphasis is placed on emissions reduction, engine efficiency, and the practicality of implementation in existing vessels. The paper concludes that while technical challenges remain—such as methanol’s lower energy density and corrosiveness—appropriate retrofitting solutions can effectively bridge the transition toward cleaner and more sustainable marine propulsion systems.

Introduction

1. Background & Motivation

The maritime industry is shifting toward cleaner fuels due to rising environmental concerns and strict IMO (International Maritime Organization) decarbonization regulations. Traditionally reliant on heavy fuel oil and diesel, the sector is exploring alternatives like methanol, which offers:

• Lower emissions (SOx, NOx, particulate matter)

• Liquid form at ambient conditions (simpler storage/handling)

• Renewable production potential (e.g., from biomass or captured CO?)

2. Retrofitting Marine Diesel Engines

Existing marine engines can be modified to run on methanol, offering a cost-effective, near-term solution. Retrofitting includes changes to:

• Fuel injection systems

• Combustion chambers

• Engine control units

3. Methanol Fuel Systems

Methanol can be supplied through Low-Pressure (LP) or High-Pressure (HP) systems, each with distinct advantages and drawbacks.

A. Low-Pressure Methanol Engines (~10 bar)

Advantages:

• Cleaner emissions (compared to conventional fuels)

• Safer operations (lower pressure = reduced explosion risk)

• Compatibility with existing infrastructure

• Simplified design and lower maintenance

• Reduced operational costs

• Potential for renewable fuel sources

Disadvantages:

• Lower efficiency than HP systems

• Dependency on pilot fuel (e.g., diesel)

• Low energy density of methanol (more storage space needed)

• Corrosive nature of methanol (material degradation)

• Limited port refueling infrastructure

• Toxicity concerns

• High initial retrofit costs

B. High-Pressure Methanol Engines (up to 300 bar)

Advantages:

• Higher thermal efficiency

• Lower pilot fuel requirement

• Reduced fuel consumption

• Lower emissions from more complete combustion

• Greater power output

• Improved cold-start performance

Disadvantages:

• Complex and expensive equipment

• Higher maintenance needs

• Safety risks due to high pressure

• Energy-intensive fuel delivery

• Corrosive effects intensified at high pressure

• High capital investment

• Infrastructure limitations for bunkering HP methanol

C. Comparison Table: Low-Pressure vs High-Pressure

4. Retrofit Methods & Engine Configurations

Dual-Fuel Combustion (Diesel + Methanol):

• Reduces NOx and soot

• Comparable performance to diesel-only operation

Injection Types:

• Direct Injection: Methanol into the combustion chamber; higher substitution possible but needs specialized injectors

• Port Injection:

  • Single-Point Injection (SPI): One injector per intake manifold

  • Multi-Point Injection (MPI): One injector per cylinder near intake valves

  • Easier to retrofit on crossflow cylinder heads than reverse-flow types

5. Industrial Developments

Companies like Wärtsilä, MAN Energy Solutions, Rolls-Royce, Hyundai Heavy Industries, and others have developed commercial methanol engine technologies with varying pressure systems and are testing them on vessels like the MV Eemsborg.

Conclusion

As the global shipping industry grapples with tightening environmental regulations and the urgent call for decarbonization, methanol has gained significant traction as a clean, scalable, and future-ready marine fuel. Retrofitting existing marine diesel engines to operate on methanol is emerging as a practical bridge between today’s fossil-fueled operations and tomorrow’s sustainable maritime landscape. This approach allows for substantial emissions reductions without requiring a complete overhaul of ship propulsion systems—a major advantage in terms of cost and feasibility. Throughout this paper, the technical, economic, and environmental dimensions of methanol retrofitting have been explored in depth. Two main fuel system configurations—low-pressure and high-pressure—were compared, each offering distinct benefits. Low-pressure systems stand out for their simplicity, lower initial cost, and operational safety, while high-pressure systems deliver higher thermal efficiency, reduced fuel consumption, and significantly lower emissions, albeit at the cost of added complexity and higher maintenance requirements. Dual-fuel strategies, including Single-Point Injection (SPI) and Multi-Point Injection (MPI), provide further adaptability. SPI systems are easier to implement but may pose challenges like engine knock and increased emissions at higher loads. MPI, while more complex, offers greater combustion control, reduced soot formation, and improved overall engine efficiency. Several key observations emerged from this study that highlight both the potential and the limitations of methanol retrofitting: 1) Methanol significantly reduces harmful emissions, including SOx, NOx, and particulate matter, making it compliant with IMO standards. 2) Retrofitting is technically viable, with necessary modifications focused on injectors, fuel lines, and combustion strategies. 3) Low-pressure systems are simpler and safer, while high-pressure systems offer better performance and fuel efficiency. 4) Dual-fuel operation balances ignition reliability and emissions control, especially in cold climates. 5) SPI is cost-effective but may lead to knocking and higher NOx, while MPI provides more precision and cleaner combustion. 6) Cold start challenges remain, due to methanol\'s low vapor pressure and high ignition temperature, requiring additional systems for reliable ignition. 7) Material compatibility is critical, as methanol is corrosive and demands the use of resistant alloys and specialized components. 8) Fueling infrastructure is still developing, but progress is being made as methanol becomes more widely adopted in global ports. In conclusion, while retrofitting marine engines for methanol use is not without its challenges—such as corrosiveness, cold start issues, and infrastructure gaps—it represents a powerful and attainable step toward decarbonizing maritime transport. By embracing the right combination of injection systems, materials, and safety measures, the shipping industry can leverage methanol’s strengths to meet both regulatory demands and environmental responsibilities. As production of renewable methanol scales and bunkering capabilities expand, retrofitting will become not just a transitional solution—but a cornerstone in the sustainable evolution of marine propulsion.

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Copyright

Copyright © 2025 Ram Priye Kumar Sahu, Ravi Rasaniya. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.