How New Alternative Fuels Are Reshaping the Marine Lubricants Landscape

Base Number (BN) / Alkalinity

• Traditional and conventional bunkers (HSFO) higher BN oils are used to neutralize sulphuric acid.
• Risk of High BN oils: Traditionally high TBN oils are used to counter the increase in the acidity of the crank case of two stroke engines. This tradition had changed post IMO 2020 after the establishment of VLSFO. The use of high-BN oils with typically high feed rates has, in many cases, resulted in over-lubrication, as observed across the industry. Thus, many engines were witnessing the problems of over lubrication, and this will tend to increase in due course due to the alternate fuels used. High alkalinity might lead to whitish deposits in the liners, piston crown, piston rings and eventually will lead to scuffing and abrasive wear. Issues of sticky ring, deposit pile up might be experienced.
• LNG, methanol, ammonia, and biofuels: Sulphur-driven acid neutralisation becomes less important, so BN requirements may reduce or shift depending on the fuel and engine design. However, acid formation from combustion does not disappear entirely.

Viscosity

• Fuel dilution: Traditional bunker fuels entering the crankcase through stuffing-box leakage can affect crankcase lubricant properties, including reducing viscosity and potentially lowering the flash point.
• Methanol and some biofuels: These fuels may increase dilution and water sensitivity, which can reduce viscosity and weaken the oil film. Fuel leakage can lower lubricant viscosity, reducing film strength and wear protection. Lower viscosity can increase the risk of bearing damage and failure, particularly in journal bearings.
• Ammonia: Ammonia has a high affinity for water and can readily form ammonium hydroxide in the presence of moisture. In fuel systems, this can contribute to corrosive aqueous phases and, where water accumulates, create conditions favourable to microbial activity. Direct effects on crankcase oil viscosity are expected to be limited; the primary lubricant concerns are corrosion control and the management of ammonia or nitrogen-containing species that may enter the oil.

Corrosion Control

• Alternative fuels such as methanol have a high affinity for water, and the potential formation of formic acid can increase corrosion and wear risks. This shifts some of the focus from acid neutralisation, while maintaining the alkalinity required for the specific fuel and engine design, towards broader corrosion control. A new approach to lubricant management is emerging, with similar considerations applying to ammonia.

Detergency / Dispersancy

• Traditional bunker fuels are generally more stable, whereas some alternative fuels can present greater stability challenges. Combustion by-products from alternative fuels may contribute to deposit build-up and, in more severe cases, sludge formation. 
• Early VLSFO operations demonstrated that some mid-BN cylinder oils required reformulation to improve detergency, dispersancy, and compatibility with new fuel types. Alternative fuels may similarly demand enhanced detergency and dispersancy properties to manage deposits and combustion by-products effectively.

Oxidation and Ageing

• Conventional fuels such as heavy fuel oil (HFO) and VLSFO can undergo oxidation, particularly during prolonged storage and heating, contributing to sludge and deposit formation. However, some alternative fuels, particularly certain biofuels, may be more susceptible to oxidation and biodegradation, potentially accelerating lubricant ageing.

Final Thoughts

In summary, alternative fuels are shifting lubricant functionality from a primary focus on acid neutralisation towards broader control of viscosity, oxidation, corrosion, deposit formation, lubricity, and water tolerance. As in any industry, unlearning and relearning will become the new norm in the marine sector.

A strong technical perspective is now essential as alternative fuels gain momentum. Price alone will no longer be the only consideration. The right lubricant must be selected with the fuel, engine design, operating conditions, and wider operational requirements in mind.

Partnering with GeoServe adds value across these considerations, providing technical insight to support bunker and lubricant procurement decisions. For a deeper discussion on these topics and the changes ahead, please reach out to GeoServe.