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Article: Use of IMO 2020 Compliant Fuels

News & Insights 13 October 2019

For members who have chosen to achieve compliance with IMO 2020 by using low sulphur fuel oil, this article serves to understand the specific aspects and variabilities of the 0.50% fuels.


With only a few months to go until the introduction of 0.50% global sulphur cap, club members should have a clarity on their compliance strategy for the IMO 2020.

For members who have chosen to achieve compliance by using low sulphur fuel oil, this article serves to understand the specific aspects and variabilities of the 0.50% fuels.

Multiple fuels are expected to bring uncertainty post-2020 and running engines reliably/safely will inevitably require greater understanding and more sophisticated fuel handling strategies than today.

Members will need to implement a proactive approach when addressing these issues. This can be achieved by making sure that the relevant ship and shore staff are aware of the fuel characteristics and efficiently manage the requirements related to the fuel oil storage, segregation, handling, switching, treatment and usage onboard.

Bunker Fuel Terminology

There are two basic types of marine fuels – distillate and residual. A third type is a mixture of these two, colloquially known as ‘intermediate’.

Distillate fuel, commonly called marine gas oil (MGO), is composed of petroleum fractions that are separated from crude oil in a refinery with a ‘distillation’ process.

Residual fuel, or heavy fuel oil (HFO), is comprised of process residues – the fractions that did not boil – and has an asphaltene content of between 3-10%. HFO also includes other products such as high sulphur fuel oil (HSFO), low sulphur fuel oil (LSFO) and ultra-low sulphur fuel oil (ULSFO).

The blends of distillates and residual fuel are described as marine diesel oil (MDO) or intermediate fuel oils (IFO). In practice, ‘marine diesel oil’ refers specifically to blends with a very low proportion of heavy fuel oil.

With IMO 2020 there is a likelihood of a number of different fuels with differing properties being sold under the umbrella term of very low sulphur fuel oil (VLSFO). These might be blends of distillates and residuals, or they might come from less traditional streams from the refinery process or by using new refining techniques.

Standards for Compliant Fuel

An assessment of the quality of a supplied fuel may be divided into three categories:

  1. Statutory requirements: SOLAS Chapter II-2 and Regulations 14 and 18.3 of MARPOL Annex VI include mandatory specific requirements for parameters such as flashpoint and sulphur content, as well as mandatory general provisions for fuel oil quality and safety. Verification of compliance with these requirements falls within the jurisdiction of the Port State in which the suppliers are registered.
  2. Defined limits: The basic requirements for marine fuels are defined in the International Organization for Standardization (ISO) 8217 standard. Fuel oil suppliers are expected to supply fuel which meets the limits in respect of certain physical properties, composition or performance indicators - as given in the Table 1 (distillate fuels) or Table 2 (residual marine fuels) test requirements of the ISO 8217 standard. 
    In accordance with ISO 8217, residual fuels are categorised into six fuel types depending on their kinematic viscosity (RMA, RMB, RMD, RME, RMG and RMK); while distillate fuels are characterised as (DMX, DMA, DFA, DMZ, DFZ, DMB and DFB).
  3. General requirements: Apart from the statutory and defined limits, the fuel oil supplied must be acceptable for use and should not contain harmful or damaging materials in concentrations that may cause damage as defined in Clause 5 of ISO 8217 and Regulation 18.3 of MARPOL Annex VI. 
    Clause 5 of ISO 8217 differs in each edition (2017 being the current) but in general terms it requires the fuel delivered to be a homogenous blend and free from materials that could cause harm to an engine or people. 
    Similar requirements are also included in Regulation 18.3.1 of the MARPOL Annex VI, which states that: 

    The fuel oil shall not include any added substance or chemical waste which either: 
    (a) jeopardizes the safety of ships or adversely affects the performance of the machinery; or 
    (b) is harmful to personnel; or 
    (c) contributes overall to additional air pollution. 

    ISO has recently published a Publicly Available Specification (PAS) 23263:2019 to help deal with new VLSFO products. The document does not include any new fuel specifications or an updated table; and is designed to be used in conjunction with ISO 8217. 
    It provides general consideration on the expected characteristics of the known new fuel products as well as providing guidance on stability and compatibility.

Distillate Fuel with FAME Content

In some locations, bunker suppliers may only be able to offer automotive diesel fuel containing biodiesel or Fatty Acid Methyl Ester (FAME) in accordance with the ISO 8217:2017 standard which provides a marine biodiesel specification (DFA/DFB) with up to 7.0% by volume of FAME.

In preparation for these situations, members are advised to check with their bunker suppliers on the extent to which biodiesel or FAME is in a fuel stem. It is recommended that shipowners and operators consult manufacturers of engines, boilers and other auxiliary equipment such as oily water separators, filters etc. in order to ensure their ability to handle these kinds of fuels.

Such fuels should be analyzed to check the total acid number (TAN) and oxidation stability. This should also include checks to determine if there is a presence of microbial contamination.

It is recommended to avoid storage periods in excess of six months to avoid fuel oxidation and degradation that could damage equipment if used in this condition.

Further information on handling these fuels can be accessed through CIMAC’s ‘Guideline for Ship Owners and Operators on Managing Distillate Fuels up to 7.0 % v/v Fame (Biodiesel)’ available on the right. 

New Fuel Risks

Industry wide there has been some flow of information about compliant fuel availability, product offering and regional supply locations. Some of the fuel testing companies have been able to sample some of the available new compliant fuel blends; however, this has been on a very limited scope so far. Anticipated issues with the new blended 0.50% sulphur fuels are:

Stability issues due to heavy blending 

Stability is the potential for a fuel to change condition in storage in certain circumstances, depending on its resistance to breakdown. Bulk fuel stored for long periods can become unstable – the asphaltene content can precipitate out of solution causing the formation of sludge. This has the potential to block filters and pipes, leaving tanks with an unpumpable residue.

The ‘break up’ is dependent on the nature of the liquid hydrocarbons in which the asphaltenes are suspended. If the medium is aromatic (hydrocarbons in ring formation) then they will remain in suspension but if it is paraffinic (linear hydrocarbon formation) the asphaltenes may have a propensity to coalesce into sludge. Once a fuel has chemically broken down there is no way to satisfactorily reverse the process. Precipitated asphaltene cannot be re-dissolved.

Compatibility issues due to use of complex fuel blends 

Compatibility is the tendency of fuels to produce deposits when mixed. The issue may immediately occur when fuels comingle. Individually, the new fuels may pass the stability criteria of the ISO 8217 but become unstable when mixed together – therefore incompatible.

The composition of blends is anticipated to vary significantly between regions. These differences raise a serious concern of incompatibility; and not just incompatibility between different products but even between batches of the same product.

Incompatibility results in sludge formation caused by precipitation of asphaltenes. This leads to blocking of filters, centrifugal separators and, in extreme cases, fuel pipes. The risk of losing propulsion or electrical power becomes very high.

In practice it is often not possible to ensure against a degree of comingling and although the rule of thumb is not to comingle or load on top in excess of 20% mix ratio, the only way to ensure there are no issues is to test a sample mix.

Testing for stability and compatibility

A number of options have been made available over the years for on-board testing (using portable test kits) to assess aspects like compatibility, viscosity, density, water and catalyst fines. However, such units are only able to provide indications. While such indications could prove useful and important, they do not provide a basis on which to challenge whether the specification has been met, or to inform decisions as to whether a fuel should be considered usable or unusable, unless the results are confirmed by an analysis at an accredited shore-based laboratory.

On the ship, one of the good ways to measure the compatibility of marine fuels is the ASTM D4740 spot test.

For this test a blend composed of representative volumes of the sample fuel and the blend stock is heated and homogenized. The ideal percentage mix is 50/50 as this is the worst-case scenario.

A drop of the blend is put on a test paper and heated to 100°C. After 1 hour, the test paper is removed from the oven and the resultant spot is examined for evidence of precipitation and rated for compatibility against D4740 reference spots.

Other concerns

  • Cold flow properties – significant operational problems may arise if supplied fuels are inappropriate for the ambient conditions. New blended products with a high distillate content are more paraffinic (linear hydrocarbon formation) in nature and could be prone to wax formation at lower temperatures.
  • Cat fines – risk of catalytic (cat) fines is predicted to increase when more products derived by secondary blending enter the market. Elevated levels of cat fines may lead to accelerated abrasive wear of engine fuel pumps, injectors and cylinder liners.
  • Lubricity – new blended products containing desulphurised components are expected be prone to lubricity problems (eg sticking of fuel pump plungers) due to the aggressive nature of the desulphurization process. These issues may result in accelerated wear of fuel pumps and injection equipment; therefore, additives may need to be added to the fuel.
  • Viscosity – large difference in viscosity (may range between 10~380 cSt (centistokes)) will affect fuel injection and combustion efficiency. Decrease in fuel oil viscosity may also cause an increase in fuel oil leakage between the fuel pump plunger and barrel of diesel engines. Internal leakages in the fuel injection system may result in reduced fuel pressure to the engine, which may have consequences for the engine performance.
  • Density – the new fuel blend densities will in general be lower than conventional residual fuel oils. This may require adjustment of centrifuges to ensure adequate cleaning of the fuel oil.
  • Total Acid Number (TAN) – some compliant fuels derived from plant and animal matter may not contain sulphur but may still have a high acidic content since the fuel is derived from fatty acids. Fuel oil with a high acid number may cause accelerated damage to various parts of the combustion unit including the fuel injection equipment.
  • Flash point – as per SOLAS, the minimum flash point of any fuel used or carried in the tanks of a ship should be not less than 60°C. Fuels with lower flashpoint (less than 60°C) will also fall outside the ISO 8217 specifications and create enhanced risk of fire and explosion. Consequently, the flashpoint of a fuel supplied to the ship should be properly verified by checking the documentation before commencement of the bunkering operations.


  • Members are recommended to carefully consider the specific technical and operational challenges that new fuel products may pose; and, where necessary contact the fuel oil supplier or original equipment manufacturers (OEM) for the considerations/preparations to be made for safer operation.
  • The ship tank configuration and fuel system may require adjustments. A fully segregated fuel system for distillate fuels and blended fuels is recommended. Ship tank configuration and segregated fuel system will also allow for better management of potentially incompatible fuels.
  • Fuel oil with very low viscosity may lead to leakages, increased wear or seizure of fuel oil pumps. Members may consider installing fuel pumps and injection nozzles suitable for such fuels. Engine and boiler makers should be consulted to ensure its safe and efficient operation. Implications for validity of NOx certification (EIAPP Certificate) should be considered.
  • While some compliant fuels may not require heating, others will require heating. It would therefore be prudent to review the heating arrangements; and where appropriate maintain the required temperature.
  • Equipment maker recommendations should be consulted for adequate testing, maintenance and possible installation of coolers etc. Also, some parts of the fuel oil supply system, ie fuel pumps, pipefittings and gaskets may need to be overhauled to ensure integrity.
  • Members shall ensure the lubricating oil and/or cylinder oil in use is appropriate for the sulphur level of the fuel being used. Advice in this respect should be sought from the engine manufacturer and lubricating oil supplier.
  • It is expected that many shipowners may initially switch to distillate fuel as a preferred method of compliance for IMO 2020; however, distillates will also have its own problems. There will be lubricity problems, micro-bled contamination and high acid corrosion, as well as cold flow. It is however possible to successfully manage cold flow properties through good fuel management, from procurement to technical operation, by considering the following:
    • ship’s trading area
    • where the risk is higher of getting fuels with poor cold flow properties
    • whether the required cold flow properties be can specified in the fuel contract
    • what the actual low-temperature flow properties of the bunkered fuel is
    • actions that must be taken in order to safely consume the bunkered fuel (eg tank and filter heating).

カテゴリ: Alternative Fuels, Pollution

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