Fuels and Lubricants

Oil fuels – the mainstay of shipping

Malcolm Latarche
Malcolm Latarche

26 June 2019

Oil fuels – the mainstay of shipping

Whatever the future of shipping may hold with regard to fuel and propulsion systems, it is generally accepted that fossil fuels will be the main source of power for the next 30 years at least. Oil fuels exist in several varieties and although it is possible for there to be an infinite number of different composition fuels, in practice the use of standard fuels is the norm. There is an ISO standard for marine fuels which is updated at regular intervals. Work on the fourth edition began in March 2008, about the same time that the IMO requested ISO to prepare a specification for marine fuels to coincide with the implementation of the Revised MARPOL Annex VI on 1st July 2010. The next version appeared in 2012 (5th edition) and the most recent in March 2017 (6th edition).

While these standards exist there is no obligation on freely contracting parties to accept only the latest or indeed any standard whatsoever. It is still a fact that the vast majority of bunker supplies are made in accordance with the earlier 8217:2005 standard. It is important when ordering fuels to stipulate exactly which standard should apply. The table on the following page details fuel types under ISO 8217-2005.

This 2005 version table is included in this guide because this older standard is still the main choice for bunker contracts despite there being two newer versions available. There were changes to some fuel types in the 2010/12 version and again in the latest version. The changes in the 2017 version are far-reaching, not least since the main change is the addition of a new set of distillate grades containing bio-fuels.

Fatty acid methyl ester(s), or FAME, has previously been regarded as a contaminant in all marine fuels, but the new grades allow bio-fuel blends containing up to 7% FAME. The main changes in the 2017 version are:

Changes to Scope:

  • The term ‘Fuels’ includes:
  • Hydrocarbons from petroleum crude oil, oil sands and shale
  • Hydrocarbons from synthetic or renewable sources, similar in composition to petroleum distillate fuels (eg hydrotreated VGO)
  • Blends of the above with FAME component where permitted

Changes to General Requirements

  • Additional distillate grades: DFA, DFZ and DFB allowing up to 7 v% FAME


Bio-diesel is a catch-all term for a wide variety of products. It is possible to produce a bio-diesel from plant material, animal material and various combinations of both. Often a small quantity of bio-diesel can be added to mineral diesel to produce a more stable fuel. There are few cases of biodiesel being used on a commercial scale in large marine engines but its use in leisure engines is more widespread.

Volvo Penta has some comments on the use of bio-diesel in leisure engines which could in some cases apply equally to larger marine engines. The comments are:

  • The biodiesel must be of good quality, which means that it must comply with the EU’s EN14214 fuel standard.
  • Biodiesel is an efficient solvent that can, when first used, dissolve constituents in the fuel system. The fuel filter should therefore be changed after a short period of usage.
  • Biodiesel is not a fuel with long-term stability, it can oxidise in the fuel system. The entire fuel system must be emptied and operated on normal diesel before any extended period of still standing, such as during winter storage.
  • Biodiesel has a negative effect on many rubber and plastic materials. Rubber hoses and plastic components in the fuel system must be checked regularly and changed at more frequent intervals than usual to avoid leakage.
  • Biodiesel impairs the lubricating capacity of oil due to its higher boiling point. The intervals for changing lubricating oils and oil filters must be halved compared with normal.

As well as bio-diesel, there is also biomethane that could be used in ships with dual-fuel engines. Biomethane is produced by the natural breakdown of organic material: green waste, household waste, agricultural waste, food industry waste and even industrial waste. The process of breaking down this material in an oxygen-free environment produces biogas, which is then purified to become biomethane which has the same characteristics as natural gas.

There are at least three methods of producing biomethane; firstly there is the anaerobic decomposition of organic waste, secondly there is gasification from ligno-cellulosic biomass (wood and straw), using a thermochemical conversion process and finally the direct transformation of micro-algae cultivated in high-yield photosynthetic reactors using natural light, water and minerals. This is an emerging technology expected to reach industrial scale use within the next decade.

Cultivating algae has the added advantage of recycling CO2 produced as a consequence of other power production rather than needing to resort to carbon capture and storage. Algae can also be processed to form oil fuel equivalents.

Making use of waste products to manufacture biofuels may be acceptable but with a growing world population it may be difficult to make a case for diverting food grade oils or using crop land for fuel production. In addition, even when crude oil prices were at their peak, the cost of producing potential biofuels made their use economically questionable. Given the decline in crude oil prices from the peak makes the cost even more unrealistic.

Low-sulphur choices

It is not certain if the refining industry will accommodate the 1 January 2020 low-sulphur deadline by producing low-sulphur fuels in the needed quantity. If it does not, then the quantity of distillates, which will be the only option to ships without scrubbers or able to run on LNG, may also be well below what is needed for the shipping industry to function.

The report on which the IMO based its decision to opt for a 2020 date included data that showed the shipping industry used 228M tonnes of heavy fuel oil in 2012 compared to just 65M tonnes of marine grade distillates. Some major upgrades to refineries will be needed if that 228M tonne figure is to be switched to low sulphur fuel oils or distillates and it should not be forgotten that other uses for refinery products are also increasing demand.

The matter of actual – rather than predicted – availability is something that will be made clearer in the coming months. If there is a shortage, then the IMO will need to rethink the regulation. In the meantime, ships operating in ECAs and some other regions where sulphur levels are limited must already meet a level of 0.1% which is below the 0.5% of the global cap.

There are some low sulphur fuel oils (LSFO) available today although the quantities available are not high and some newer ultra-low sulphur fuel oils (ULSFO) – sometimes referred to as hybrid fuels – have been developed to meet the 2015 reduction to 0.1% in ECAs. The first generation of low-sulphur fuels was quickly followed by newer products and some refiners are working on newer versions still to meet the 2020 rules. Some are already becoming available.

At the present time, ULSFO fuels are used mostly in ECAs and special precautions are needed during switchovers. This will be less of a problem when fuels with a sulphur content of 0.5% do become readily available as the switchover will be between fuels that are potentially much more similar in properties. Potential compatibility issues may occur between fuels from different suppliers and this is one of the issues identified during the IMO discussions that is not yet resolved satisfactorily. More information on this is included in Resolution MEPC 320(74).

The fuels can be very different in characteristics from conventional fuel oil and this has led numerous organisations to issue guidance to operators on their use. Lloyd’s Register issued the following advice in its publication Using hybrid fuels for ECA-SOx compliance.

Most of the new hybrid fuels are blended products and have some characteristics of distillate products. This means they may exert a ‘cleaning’ action, mobilising previously deposited asphaltenic material, potentially leading to increased filter loading and other operational issues. It is therefore recommended that fuel tanks which will carry these new fuel types are cleaned or at least cleared of the ‘unpumpables’ at the tank bottom.

Despite their distillate characteristics, most of these hybrid fuels are particularly waxy in nature, as exhibited by their pour points (the lowest temperature at which a fuel will continue to flow). The exact pour point may vary from product to product, but the usual rule is to maintain any fuel oil no lower than 7°C above its tested pour point. These fuels therefore need to be stored and handled in systems with heating arrangements.

These types of fuels should not be stored in tanks which are subject to low external temperatures, such as a ship’s side tanks. Even in tanks with heating coils that maintain the bulk of the fuel as liquid, the formation and then breakaway of material at the cold interface could result in operational problems.

These fuels will also need to be purified, taking into account their density (gravity disc selection) and viscosity for optimised preheat. Based on the tested viscosity and density of the fuels, the purifier manufacturer’s recommendations should be followed for the correct operational adjustments.

Advice has also been issued by other class societies, P&I clubs, engine makers and the USCG on safe switchover procedures when entering ECAs. Much of the advice is a repeat of that needed some years ago when the EU imposed a 0.1% sulphur cap on fuel used during port stays within the EU but, with many more ships and owners now affected, repeating it is probably a wise precaution.

In the run up to 2020, many of the oil majors have developed new bunker fuels with a sulphur content of 0.5% or below. There has been much speculation as to the miscibility of fuels from different suppliers and although the suppliers have tried to allay fears, concerns continue to exist and will only be satisfied once more experience is gained.

Distillate fuels

Distillate fuels such as DMA and DMB, usually referred to as MGO and MDO respectively, are frequently used in the main engines of most ships not running on ULSFO or fitted with scrubbers and operating in ECAs and by smaller ship types as a normal fuel of choice. Distillates also power most auxiliary engines on all ship types although some larger vessels will use IFO when possible.

They are available in standard and low sulphur versions with the former currently averaging 1-1.5% sulphur and the low sulphur version being ECA compliant at 0.1%. Of the two main types mentioned, MGO is the lightest and contains least sulphur. MDO is effectively MGO with a small proportion of residuals and is likely to have a higher sulphur content.

Because they can be used in main engines normally run on HFO, distillates represent the easiest means of meeting the 0.5% global cap if availability is the main criterion. However, although readily available, distillates currently account for less than 25% of all marine fuels used. They are also heavily used in many non-marine sectors in far greater quantities including in power production, road, rail and off-road plant, agriculture and many other industries.

An increased use of distillates as a means to meet the 0.5% sulphur cap will therefore bring the shipping industry into competition with other users with no guarantee that sufficient supplies will be available. Increased use of distillate fuels for shipping generally will also badly impact those ships that have been specifically designed to operate with them and which are mostly employed in short sea trades and for local passenger and cargo ferries.

Emulsified fuels

Water in fuels can be a problem and most engine makers traditionally recommend that water in HFO should be removed entirely by separation before entering the engine. This is mostly due to the fact that cat fines are more easily transported in water and sea water in the fuel oil is a major source of sodium. This, along with ash and vanadium are to be avoided where possible because compounds of the chemicals tend to promote mechanical wear, high temperature corrosion and the formation of deposits in the turbocharger and on the exhaust valves.

However, controlled use of water such as humid air, direct water injection and emulsion fuels can be beneficial in reducing levels of NOx and SOx. While the first two options are for engine makers to research and develop, the last option is receiving attention from some specialists in the fuel sector.

Emulsified fuels work by using a quantity of water in the fuel which has the effect of reducing the size of oil droplets compared to conventional fuels. This results in more complete combustion of the oil and so increases the energy delivered from a given quantity of fuel. Because the oil droplets surround a water core, the heat in the combustion chamber also causes the water to vaporise which breaks the oil down into even finer droplets. The water vapour itself adds energy much as it would in a steam engine.

Although the governor of an engine running on such fuel may open up more to meet the speed demand set by the bridge, the volume of water contained in the emulsion will more than cover the extra amount of emulsified fuel injected. Therefore, the fuel saving will be equal to the volume of water contained in the fuel less the extra percentage of emulsified fuel injected.