The Benefits of Using Biofuels in Marine Diesel Engines

Marine transportation underpins global trade, moving over 80 percent of the world’s goods by volume. Yet the sector also accounts for nearly three percent of global greenhouse gas (GHG) emissions, along with significant volumes of sulfur oxides, nitrogen oxides, and particulate matter. In response to tightening regulations from the International Maritime Organization (IMO) and growing pressure from charterers and consumers, shipowners and operators are exploring alternatives to conventional heavy fuel oil and marine gas oil. Biofuels have emerged as one of the most immediately viable drop‑in solutions for existing marine diesel engines. Derived from renewable biological sources such as vegetable oils, animal fats, used cooking oil, or algae, biofuels offer a pathway to reduce lifecycle GHG emissions without requiring extensive retrofits. This article explores the environmental, economic, and operational benefits of using biofuels in marine diesel engines, examines the challenges that remain, and outlines realistic pathways for broader adoption.

Environmental Benefits

Reduction of Lifecycle Greenhouse Gas Emissions

The most widely cited advantage of biofuels is their potential to lower net carbon dioxide (CO₂) emissions. Unlike fossil fuels, which release carbon that has been sequestered for millions of years, biofuels are produced from biomass that absorbs CO₂ during growth. When the fuel is burned, that carbon is re‑released, creating a closed carbon loop. Depending on the feedstock and production method, lifecycle GHG reductions of 50 to 90 percent compared to conventional marine gas oil (MGO) are achievable. For example, hydrotreated vegetable oil (HVO) produced from waste feedstocks can reduce well‑to‑wake emissions by up to 85 percent. Fatty acid methyl ester (FAME) biodiesel made from used cooking oil typically delivers a 60–80 percent reduction. These figures are validated by certification schemes such as ISCC EU and RSB, which are recognized under the IMO’s Data Collection System (DCS) and the EU’s FuelEU Maritime regulation.

Drastic Reduction in Sulfur Oxides and Particulate Matter

Conventional heavy fuel oil can contain up to 3.5 percent sulfur, and even low‑sulfur marine gas oil has a maximum limit of 0.1 percent in Emission Control Areas (ECAs). Biofuels, by contrast, are virtually sulfur‑free. HVO and FAME typically contain less than 10 ppm of sulfur, meaning they do not require scrubbers or expensive distillate fuels to comply with IMO’s global 0.5 percent sulfur cap. In addition, the absence of aromatic hydrocarbons and the high oxygen content of biodiesel lead to more complete combustion. This results in reductions of particulate matter (PM) emissions by 50–80 percent compared to MGO, along with lower smoke opacity. The cleaner exhaust contributes directly to improved air quality in ports and coastal communities, a growing concern as local governments impose stricter emission standards on shipping.

Lower NOx and CO₂ Trade‑Offs

One common concern with biodiesel is that its higher oxygen content can increase nitrogen oxide (NOx) formation under some engine conditions. However, engine tuning, injection timing, and the use of blend levels below 20 percent can mitigate this effect. Many modern marine engines equipped with common‑rail injection systems can run on B20 to B30 blends with no measurable NOx increase. Moreover, some HVO formulations actually reduce NOx by 5–10 percent due to better combustion characteristics. Early adopters report that optimization of the engine management system allows biofuels to achieve IMO Tier III NOx compliance when used in combination with exhaust gas recirculation (EGR), without needing selective catalytic reduction (SCR) in every operating mode.

Biodegradability and Spill Mitigation

Biofuels are significantly more biodegradable than petroleum‑based diesel. In the event of a spill, FAME biodiesel degrades about four times faster than conventional diesel and is far less toxic to marine organisms. This property is especially valuable for vessels operating near sensitive ecosystems, such as ferries in coastal waters, fishing fleets, and marine research ships. While HVO has somewhat lower biodegradability than FAME, it still outperforms mineral diesel. Operators concerned with environmental liability and compliance with MARPOL Annex I may find that the reduced clean‑up requirements and lower ecological damage profile of biofuels represent an underappreciated advantage.

Economic and Operational Benefits

Drop‑In Compatibility and Minimal Retrofits

One of the most compelling reasons for adopting biofuels is their ability to function as a drop‑in replacement in existing marine diesel engines without major modifications. Both FAME and HVO can be used in blends with conventional marine diesel oil (MDO) or MGO up to certain limits. Many engine manufacturers—including Wärtsilä, MAN Energy Solutions, and Caterpillar—have issued statements confirming compatibility with up to 30 percent FAME (B30) in standard engines, while HVO is approved at even higher blend ratios. For newer engines designed to handle higher viscosity and lower lubricity of some biofuels, B100 or HVO100 operation is feasible with only minor adjustments to seals and filters. This drop‑in nature dramatically reduces the capital investment required compared to switching to LNG, methanol, or ammonia, which require completely new engines or extensive retrofit packages.

Enhanced Lubricity and Engine Wear Reduction

Biodiesel has inherently better lubricity than low‑sulfur diesel, which has been stripped of natural lubricants during hydrodesulfurization. The fatty acid chains in biodiesel form a thin boundary layer that protects fuel injection components—pumps, injectors, and nozzles—from wear. In a laboratory test at the US National Renewable Energy Laboratory (NREL), B20 blends showed as much as 40 percent less wear on pump components compared to low‑sulfur diesel. For older marine engines that rely on fuel for lubricating the injection pump, this can extend overhaul intervals and reduce maintenance costs. Fleet operators running blends above B10 routinely report longer injector life and fewer clogged nozzle failures, translating into tangible savings in parts and labor.

Energy Security and Price Stability

Biofuels can be produced locally from a wide variety of feedstocks—rapeseed in Europe, soy in the Americas, palm oil in Southeast Asia (though controversial due to deforestation), and waste feedstocks globally. For nations reliant on importing crude oil, developing a domestic biofuel supply chain enhances energy security and reduces exposure to volatile crude prices. While the spot price of biodiesel has historically been higher than that of marine gas oil—often by 30–80 percent—government incentives such as the EU’s Renewable Energy Directive (RED III) and the US Renewable Fuel Standard (RFS) provide compliance credits that can offset the premium. In addition, the price gap has been narrowing as production scales and oil prices rise. During 2022–2023, when crude oil spiked above $100 per barrel, B100 from used cooking oil in the ARA region (Amsterdam‑Rotterdam‑Antwerp) was at times price‑competitive with conventional MGO on an energy‑adjusted basis.

Availability of Incentives and Compliance Credits

The IMO’s Carbon Intensity Indicator (CII) and the upcoming FuelEU Maritime regulation (effective 2025) assign GHG intensity scores to fuels. Biofuels that meet strict sustainability criteria—typically a 50–65 percent reduction in well‑to‑wake emissions relative to a fossil reference—receive a low carbon intensity rating. Ships using such biofuels can improve their CII rating and avoid penalties. In the EU, operators that blend biofuels into their marine distillates can claim compliance credits against the FuelEU Maritime GHG intensity target, effectively transferring the carbon abatement value to their compliance obligations. Several European ports, including Rotterdam, Hamburg, and Antwerp, offer discounts on port dues for vessels using alternative fuels, with biofuels explicitly included. Moreover, under the IMO’s planned mid‑term measures (2025–2030), a fuel‑based pricing mechanism or levy is expected to create further economic incentives for low‑carbon fuels.

Operational Case Studies

Maersk’s biofuel trial: In 2021, Maersk successfully operated a container vessel on a blend of 20 percent waste‑based FAME and 80 percent MGO for over 12 months. The trial concluded that the blend performed flawlessly in the main engine and auxiliary engines, with no fuel‑related downtime or maintenance issues. Maersk subsequently expanded the use of sustainable biofuels to a fleet of more than 60 vessels.

The Stena Line example: The Swedish ferry operator has been using HVO in several of its ro‑pax vessels since 2019. The switch reduced annual CO₂ emissions by approximately 10,000 tonnes per ship. Stena Line reported that fuel consumption remained virtually unchanged, and that HVO required no modifications to the ferry’s four‑stroke auxiliary engines. The HVO was sourced from certified waste feedstocks and delivered via existing bunkering infrastructure.

Ocean Infinity’s robotic vessels: The offshore survey company Ocean Infinity operates a fleet of autonomous and crewed ships, including the 78‑meter “Normand Frontier,” which runs on B100 from used cooking oil. The vessel has logged more than 15,000 engine hours on B100 since 2020, with no fuel system failures. The company found that the higher cetane number of biodiesel improved cold‑start performance, and that engine oil change intervals could be extended by up to 20 percent after analysis of used oil showed lower oxidation than expected.

Types of Biofuels for Marine Engines

FAME (Fatty Acid Methyl Ester)

FAME biodiesel is produced through transesterification—reacting vegetable oils or animal fats with methanol. It has a high cetane number (50–65), excellent lubricity, and low toxicity. However, its high oxygen content and tendency to oxidize over time impose restrictions on storage life (typically 6–12 months). FAME also acts as a solvent, loosening deposits in fuel tanks that may clog filters during the initial transition. For marine use, EN 14214 (European standard) specifies strict limits for water content, glycerin, and storage stability. Engine manufacturers generally recommend blend levels up to B30 (30% FAME) for continuous use, with B100 limited to engines specifically designed for it—often with modified elastomers and corrosion‑resistant injection pumps.

HVO (Hydrotreated Vegetable Oil)

HVO is produced by hydrotreating animal or vegetable fats with hydrogen, yielding a paraffinic hydrocarbon that is chemically identical to highly refined diesel. Unlike FAME, HVO is a pure hydrocarbon, so it has no oxygen content and does not attract water or support microbial growth. It has an extremely high cetane number (70–85), very low sulfur and aromatics, and unlimited storage stability. HVO is fully miscible with conventional diesel at any ratio, making it an ideal drop‑in fuel for any marine diesel engine (including high‑pressure common rail systems) with no modifications required. The main drawbacks are cost—HVO is typically 20–50% more expensive than MGO—and limited global production capacity, most of which is concentrated in Europe and North America. However, new HVO plants are under construction in Asia and the Middle East, which will improve supply chains for shipping.

Advanced Biofuels from Algae, Lignocellulosic Biomass, and Waste

Second‑generation biofuels derived from non‑food feedstocks are gaining attention for marine use. Algae‑based fuels can achieve extremely high oil yields per hectare and can be cultivated on non‑arable land. Algae biodiesel has properties similar to FAME but with higher oxidative stability. Lignocellulosic feedstocks (such as wood residues, corn stover, or energy crops like miscanthus) can be converted via gasification and Fischer‑Tropsch synthesis into drop‑in synthetic diesel. The EU project “BioMare” has demonstrated the feasibility of producing marine diesel from forest residues. While still at pilot/commercial scale, these advanced fuels avoid the food‑versus‑fuel debate and can achieve GHG reductions exceeding 90 percent. Some industry forecasts predict that advanced biofuels will account for a quarter of marine fuel demand by 2050.

Sustainability Certification and Land‑Use Concerns

To qualify for regulatory incentives, biofuels must meet strict sustainability criteria. The EU’s Renewable Energy Directive (RED II and III) requires that feedstocks not cause deforestation, displacement of food production, or loss of biodiversity. Waste‑based feedstocks (used cooking oil, animal fats, tall oil) receive double counting toward national renewable energy targets. The risk of indirect land‑use change (ILUC) is a major concern for crop‑based biofuels; palm oil biodiesel, for instance, has been associated with deforestation in Southeast Asia and is effectively excluded from many incentive programs. Well‑performing biofuels for marine use should be certified under ISCC EU, RSB, or similar voluntary schemes to ensure that they are produced from sustainable sources. Ship operators should request evidence of chain‑of‑custody certification and carbon intensity data from their suppliers to ensure compliance and avoid reputational risk.

Challenges and Technical Considerations

Oxidation Stability and Storage Life

FAME biodiesel oxidizes over time, forming acids and polymerized deposits that can clog filters, increase injector deposits, and degrade fuel quality. Storage in a marine environment—with warm ambient temperatures, moisture, and steel tanks—accelerates this process. Operators have several mitigation measures: use of antioxidants (such as BHT), blending with stabilizers, ullage gas blanketing (nitrogen), and tank cleaning prior to biofuel introduction. Regular fuel quality testing (per ASTM D6751 or EN 14214) is essential. HVO, by contrast, does not degrade and can be stored for years without deterioration, making it the preferred choice for vessels that carry fuel for long periods.

Microbial Growth and Water Contamination

Biodiesel is more hygroscopic than conventional diesel and absorbs water from the atmosphere or condensation. Water and free fatty acids provide a breeding ground for microorganisms—bacteria and fungi—that produce sludge and corrosion. Filtration, water separation, and the use of biocides (such as isothiazolinone) are standard practice. Operators using FAME should install larger water separator elements and monitor fuel tank bottoms for water accumulation more frequently. Again, HVO’s hydrophobicity eliminates this issue, giving it a major operational advantage for ocean‑going vessels.

Material Compatibility

Early transition trials revealed that biodiesel degrades certain older elastomers: natural rubber, Buna‑N, polyurethane, and neoprene. Fuel hoses, seals, and gaskets may swell, soften, or crack when exposed to high concentrations of FAME. Manufacturers now supply fuel systems with FKM (Viton®) or PTFE‑lined components that are resistant to biodiesel. For a fleet transitioning to B30 or higher, a pre‑inspection of all fuel‑wetted materials is recommended and cost‑effective replacements should be scheduled. HVO poses no material compatibility issues because it is identical to fossil diesel.

Cold‑Weather Performance

FAME biodiesel typically has a higher pour point and cloud point than conventional diesel. Pure FAME (B100) can gel at around 0°C (32°F), making it unusable in cold climates without heating. Winterization—blending with diesel, using pour‑point depressants, or selecting feedstocks with lower saturation (e.g., camelina vs. palm)—can lower the cold‑filter plugging point (CFPP) to –15°C or lower. HVO has a very low pour point (–32°C), comparable to premium winter diesel, so it performs well in polar regions. Vessels operating in Arctic or Northern European routes should specify HVO or a winter blend with adequate CFPP margins.

Supply Chain and Bunkering Infrastructure

While biofuel bunkering has grown rapidly—Rotterdam now supplies over 500,000 tonnes per year of blended bio‑marine fuels—the availability remains limited outside major hubs. Ports such as Singapore, Fujairah, and Houston lack dedicated biofuel storage and blending facilities. The physical properties of FAME (higher density, hygroscopicity) mean that it cannot be co‑mingled with heavy fuel oil; dedicated tanks and lines are required. HVO, being hydrocarbon‑like, can be handled in existing diesel infrastructure. Scaling the supply chain will require investment in dedicated storage, blending terminals, and bunker barges. Collaboration between fuel producers, ports, and shipping lines is increasing, and several joint‑industry projects (such as “GoodShipping”) are piloting supply‑chain solutions.

Regulatory Landscape

IMO’s Initial GHG Strategy and Mid‑Term Measures

The IMO’s Initial Strategy (2018) aimed to reduce GHG emissions from shipping by at least 50 percent by 2050, relative to 2008. In July 2023, the IMO adopted a revised strategy targeting net‑zero GHG emissions “close to 2050,” with indicative checkpoints of 20‑30 percent reduction by 2030 and 60‑80 percent by 2040. Biofuels are explicitly recognized as a key lever in the IMO toolbox, alongside energy efficiency, speed optimization, and future fuels. The mid‑term measures (expected 2025‑2027) will include a marine fuel standard (GHG intensity limit) and a pricing mechanism—either a levy on fossil fuels or a reward for low‑carbon fuels. Biofuels that meet sustainability criteria will likely be eligible for a zero or reduced GHG rating, giving them a pricing advantage over conventional fuels.

EU FuelEU Maritime and the ETS

Europe is leading the regulatory push. FuelEU Maritime (effective 2025) sets a declining GHG intensity target for energy used on ships calling at EU ports, starting with a 2 percent reduction in 2025 and ramping to 80 percent by 2050. Fuels are scored by their lifecycle emissions; standard marine gas oil scores ~91 gCO₂eq/MJ, while most waste‑based biofuels score around 20–40 gCO₂eq/MJ—far below the target. Ships that use biofuels will gain compliance surplus that can be banked or traded. Additionally, shipping is now included in the EU Emissions Trading System (EU ETS), requiring operators to surrender allowances for a portion of their emissions (40% in 2024, then 70% in 2025, 100% in 2026). Using a biofuel that is classified as having zero CO₂ emissions under ETS rules (because the biogenic carbon is accounted at source) directly reduces the number of allowances needed, offering a substantial cost saving.

California and Other Regional Programs

In the United States, the California Air Resources Board (CARB) regulates ocean‑going vessels within 24 nautical miles of the coast. CARB’s Ocean‑Going Vessel Fuel Rule requires the use of distillate fuels (0.1% sulfur) but does not mandatorily restrict carbon intensity. However, the Low Carbon Fuel Standard (LCFS) provides credits for suppliers of low‑carbon marine fuels, including biofuels. Similar programs exist in Oregon (Clean Fuels Program) and British Columbia (Low Carbon Fuel Requirements). Japan, South Korea, and Singapore are developing national roadmaps for alternative marine fuels, with biofuels explicitly included.

Future Outlook and Recommendations

Scaling Production and Reducing Costs

The global production of HVO is expected to double from 9 million tonnes in 2023 to over 18 million tonnes by 2028, driven by new plants in the US, Europe, and Southeast Asia. FAME production is more mature but increasingly oriented toward waste feedstocks. Advanced biofuels from algae and lignocellulosic biomass remain at pre‑commercial scale but could reach cost parity with fossil diesel by 2040 with sustained R&D investment. Economies of scale, process optimization (e.g., using renewable hydrogen for HVO production), and carbon pricing will all contribute to narrowing the price gap. Shipping lines that secure long‑term offtake agreements today can lock in prices and guarantee supply, gaining a competitive edge as regulations tighten.

Technical Recommendations for Operators

  • Start with low blends: B10 to B20 for FAME; any blend ratio for HVO. Monitor fuel filters closely during the first 500 hours of operation.
  • Conduct a material compatibility audit: Inspect all fuel hoses, gaskets, and tank coatings; upgrade to Viton or PTFE where needed.
  • Implement rigorous fuel quality testing: For FAME, test for acid number, viscosity, water content, and ester content every bunkering. For HVO, ensure that the fuel meets EN 15940 (paraffinic diesel standard).
  • Adjust storage and handling procedures: Keep fuel tanks as full as possible to minimize condensation. Use biocides in FAME‑based systems. Consider nitrogen blanketing for long‑term storage.
  • Partner with certified sustainable suppliers: Only purchase biofuels with ISCC or RSB certification to guarantee regulatory compliance and avoid greenwashing claims.
  • Explore charterer demand: Major shippers—Amazon, IKEA, Unilever—are committing to zero‑carbon shipping. Using biofuels can secure premium cargo contracts and demonstrate environmental leadership.

Conclusion

Biofuels are not a silver bullet—scalability, cost, and supply chain limitations remain significant barriers. Yet they are the most technically mature, operationally manageable, and immediately available low‑carbon option for the vast majority of the world’s 60,000+ commercial vessels powered by diesel engines. Unlike LNG or ammonia, biofuels require little to no capital investment and deliver drop‑in compatibility. Regulatory tailwinds—IMO targets, FuelEU Maritime, EU ETS, and national policies—are creating a growing economic incentive for their adoption. Shipping companies that begin trialing and scaling biofuel use now will be better positioned to meet tightening emissions limits, improve their CII ratings, and build a reputation as low‑carbon leaders. The path forward involves continued investment in sustainable feedstock supply, improved logistics, and cross‑industry collaboration. But the trajectory is clear: biofuels will play an indispensable role in decarbonizing marine transportation for the next two decades and beyond.

For further reading: IMO GHG Strategy | CIMAC Biofuel Guidelines | DNV Biofuel Guide | ISCC Certification | US DOE Marine Biofuels