A Deeper Study on VLSFO

Exhaust Scrubbers FAQs Answered | Latest Maritime Updates | COVID-19
9 Scrubber FAQs Answered
May 15, 2020
Deeper Study On VLSFO Issues With VLSFO Usage - Kamelia Cleantech


With the IMO 2020 regulations already in effect on January 1st, 2020, there has been a dramatic shift in the dominant bunker fuel, shifting from Heavy Fuel Oil (HFO) to the new 0.5% Sulphur Very Low Sulphur Fuel Oil (VLSFO). Although the change has seemed relatively smooth, there have been alarming signs that the so-called “cleaner fuels” may possess greater implications for the ship engines than previously anticipated.

Slipping under the radar?

Bunker fuel quality from major ports has come under scrutiny after several usages, as well as compliance issues, have been reported. Although most of these occurrences are related to fuel stability issues and sediment deposits, over 8% of VLSFO batches tested in 2019 exceeded the 0.5% sulphur limit[1], making the fuel incompliant. Furthermore, there is a significant number of instances where new blends of fuel do in fact pass current industry standards and testing, despite containing harmful components that are usually not tested for. 

No longer “Fit-for-purpose”?

Most marine fuel systems and engines have been optimised for HFO usage. A large proportion of vessels would need major modifications to help them cope with the less viscous new blends. Most engine manufacturers have needed to publish detailed guidelines for vessel owners. Wartsila estimates that a quarter or more of the 1,100 vessels, mainly large containers and tankers, using their two-stroke engines (now under WinGD brand name) would require engine upgrades[2]. Starting difficulties and engine damage were reported due to premature wear of cylinder linings and valve seats, which is mainly caused by catalytic fines used in low-temperature fuel refining.

Recent reports in the headlines

  • 7 bunker alerts issued by VFS relating to sediment issues, between December 24, 2019, and January 21, 2020, for fuel supplied in: Singapore, Piraeus, Amsterdam, Rotterdam, Miami and San Vincente[1]
  • FOBAS issued alerts in May 2020 after testing fuel in Antwerp falling below SOLAS flashpoint limit[3]
  • Six samples of ship fuel in Singapore were tested in 2018 where severe sludging at centrifuges, clogged pipelines, and overwhelmed fuel filters where detected. [4]
  • The first problem sample in Asia was found on April 13, 2018, in Port Kelang in Malaysia, which led to a dead ship that had to be towed back to port with all fuel pumps damaged. [4]
  • Contaminated bunkers observed in the US Gulf in 2018- more than 100 vessels experienced system clogging and engine damage. [4]

Issues with VLSFO [5]

Stability issues

  • Stability is the resistance to breakdown and precipitation of asphaltenic sludge in normal operating conditions. Once precipitated, process cannot be reversed.
  • Certain blends, are either already unstable or on the verge of being unstable.
  • Stability issues occur when the fuel is blended such that the asphaltenes are not well suspended and if fuel does not have enough aromatic components to keep asphaltenes in suspension.
  • Sludge accumulation in the storage tank, piping systems or centrifuges and filters causes purifier and filter choking.

Compatibility issues 

  • Compatibility is the ability of two or more fuels to be mixed without material separation
  • The new 0.5% S marine fuels are mostly paraffinic and mixing them with aromatic fuels pose a risk for incompatibility.
  • This could result in the formation of flocculation or separation of asphaltenes, precipitating sludge, blocked filters and separators 

Catalytic fines 

  • Catalytic fines are hard aluminium and silicon oxide particles that are normally present in HFO & VLSFO as a result for low-temperature fuel cracking refinery process
  • Catalytic fines in fuels should not exceed 15 mg/kg (ppm). In some regions, the average content of cat fines in VLSFO is almost double that found in HFO
  • High levels can cause damage to engine fuel injection equipment and pistons/liners requiring an overhaul, reconditioning or in worst cases, complete cylinder head replacement.

Cold flow properties issues 

  • Possible wax formation due to high paraffin content in many VLSFOs
  • Wax crystals form during handling if temperature descends below the wax appearance temperature (WAT) 
  • Wax formation causes blocked filters, deposits in the storage tank and reduced fuel flow rate to the machinery

Ignition and combustion properties

  • Most paraffinic fuels have good ignition-combustion properties while aromatic fuels have poor ignition combustion
  • VLSFOs can be paraffinic, aromatic or mixture of paraffin/aromatic so ignition-combustion properties of fuel need to be evaluated
  • Fuels with poor ignition and combustion properties can cause engine damage and even total breakdown

Corrosion issues 

  • Shipowners need to be aware that the new fuels may contain a significant amount of acids despite being classified as low sulphur
  • Total acid number (TAN) of fuel needs to be tested 
  • Fuels with high TAN need to be used with appropriate lubricating oils to prevent engine damage

Low viscosity 

  • The heating systems are designed for HFO (16cst – 24cst) and not designed for a mixture with LFO (6 cst)
  • The lower viscosity will reduce the film thickness between the fuel pump plunger and casing causing excessive wear, possible sticking, and failure of the fuel pump
  • Leaking fuel around the pump plungers and rotors prevents the ship from achieving full power


  • Flashpoint is one of the valid indicators of fire and explosion hazard posed by the fuel
  • There is a possibility of a decreased flashpoint in low sulphur fuels because of different characteristics of the blending component feedstocks and method of production
  • A low flash point means an increased risk of fire and explosion. SOLAS limit of 60°C has no tolerance and vessels may risk losing their insurance if an accident occurs on board as a result

Unusual constituents

  • Possibility of contamination by Polymers, Polymethacrylates, Phenols, Tall oils, and Chlorinated hydrocarbons which can all be related to blending. 
  • Can cause filter blocking, pump sticking, fuel pump seizures and excessive separator sludging


Current experience with the use of VLSFO is mostly limited to the past six pandemic-ridden months, where there have been unusually low levels of marine traffic. The industry is still on a learning curve when it comes to best practices for VLSFO, with engineers attempting to quickly adapt to the new regime; but now is not the time for complacency. Shipowners and operators have the option of a futureproof, long-term savings strategy- continuing to use reliable HFO by choosing to install exhaust gas scrubbers. Here at Kamelia Cleantech, we are well-positioned to aid shipowners and operators of both small and large vessels to achieve significant savings and a higher return on investment with our technology.

  1. https://www.spglobal.com/platts/en/market-insights/latest-news/oil/020320-bunker-fuel-quality-issues-surge-as-vlsfo-use-gathers-pace-sources
  2. https://shipandbunker.com/news/world/888560-several-hundred-ships-may-need-engine-upgrades-to-cope-with-vlsfo
  3. https://shipandbunker.com/news/world/489052-fobas-alert-low-flash-point-distillate-marine-fuel-oil-in-antwerp
  4. https://mfame.guru/sediment-problems-observed-from-vlsfos-at-six-ports/
  5. https://mfame.guru/vlsfo-from-unknown-fuels-blend-can-cause-operational-issues/

Leave a Reply

Your email address will not be published. Required fields are marked *