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Synthetic lubricants

Updated 11 Oct 2019

STENA GERMANICA 75ng235c7

Lubricants are usually produced using a mineral oil base with additives but even with the best quality controls in place, natural variability in the base oils means that performance can sometimes be less than expected and furthermore the base oils themselves are sometimes not ideally suited to the environment they are used in. In attempting to gain more uniform and improved performance, most leading manufacturers now offer synthetic products.

Most will claim that synthetic lubricants offer superior protection and performance compared to conventional mineral oils and that they have a longer service life in the engine, decaying at a known rate and therefore giving predictable performance. Other claimed advantages include high-temperature capability, low-temperature flow properties and a resistance to oxidation.

Tests do tend to show an improved performance that agrees with the makers’ performance claims but for the operator the downside is that synthetic lubes come with a premium price tag.

It will be for the operator to decide if the benefits outweigh the price premium or if the extra cost can indeed be clawed back through longer life. It is however important to investigate miscibility with other products if synthetic lubes are chosen.

Most operators chose to use lubricants from a single maker whenever possible but even the best laid plans can go awry and it is sometimes necessary to use products from different suppliers. Except for a few specific lubricants, most manufacturers have equivalent products that can safely be used alongside competing products. Ensuring the compatibility of products before mixing is relatively simple as most makers produce charts listing compatible rival offerings.

The reduction of the IMO’s global cap on fuel sulphur levels in 2020 will lead to demand for a new generation of lubes and if refiners choose to produce HFO with the 0.5% limit rather than continue with the current 3.5%, some of today’s products will become obsolete except for those ships with scrubbers that can continue to use the higher sulphur fuels.

It might be thought that the difference between 0.5% and 0.1% is small enough to make the need to change lubricants when entering ECAs in future unnecessary. However, many experts believe that the need to match cylinder lubricants to the fuel will continue after 2020 and, for ships operating with high sulphur fuels and scrubbers, lubes with higher BNs will be needed because the scrubbing takes place after combustion.

2020-compliant fuel oils bring their own problems

For the ships that are going to run on compliant fuels, cylinder lubrication will not necessarily become simpler just because only two grades of fuels (0.5% and 0.1% sulphur content) will be used. Many of the new fuels will be blended and as ships move between ports, the available fuels may have very different qualities and characteristics. Some of the fuels may contain biofuels in varying quantities and a very small number of vessels may be run wholly on biofuel.

Most common biofuel types include fatty acid methyl esters (FAME), ethanol and hydrotreated vegetable oil (HVO). These fuels can exhibit very different properties than traditional oil fuels and may even have a higher acid content with no sulphur present at all.

Blended fuels and biofuels may also have very different viscosities and combustion characteristics which will make the choice of an appropriate lubricant an important factor in operation and maintenance.

Most of the leading lubricant suppliers have spent much time and effort in developing lubricants suited to the new range of fuels that will be used after 1 January 2020 and are gradually introducing these to the market. The full range of new products may currently have limited availability and so gathering experience with them in conjunction with new fuels will not be the easiest of tasks.

For ships that have regular routes or areas of operation, some experimentation of new fuels and new lubes may be possible but involving OEMs, lubricant suppliers and testing services would be a prudent precaution.

Custom-made lubes

Almost all engine lubes are sourced from specialist manufacturers but the ability to produce a useful lube on board is now possible on some vessels. Maersk Fluid Technology (MFT) – an A P Møller subsidiary – has been experimenting and developing blending on board (BOB) as an alternative solution for some years.

The system has been implemented on some Maersk vessels and is now being commercialised as the SEA-Mate Blending- On-Board system. The concept is based on proprietary technology designed to enable the operator to custom blend a fit-for-purpose cylinder lubricant from recycled in-use two-stroke system oil and a high BN cylinder oil concentrate.

Some ship engineers also do something similar but without the use of sophisticated equipment and manually blend the stem oil with an additive.

Alternative fuels and two-stroke engine lubrication

In recent years the number of alternative fuels to oil that are being used, or may be used in the future, by ships has grown to include LNG, LPG, methanol, ethanol and ethane with hydrogen and ammonia being other recent newcomers. That all of these fuels could, with some modifications, be used in an engine that can also burn mineral oil fuels and biofuel variations is a testament to the versatility of the diesel engine and a good reason why its demise is not seen as being something that will happen anytime soon.

Operations with LNG in four-stroke dual-fuel engines are nothing particularly new but there is much less experience gained on dual-fuel two-stroke engines. While quite a number of these have now been fitted – almost 250 are in service at mid-May 2019 – many are only considered as gas-ready with no gas fuel system in place so are presently running as typical fuel oil burning engines.

The dual-fuel engines that can run on LNG are not the only two-stroke power units using alternative fuels. There are for example 10 ships in service that are using methanol as a fuel – nine of them with two-stroke engines and the Stena Germanica as the only four-stroke conversion so far. Methanol is a liquid fuel that is considered a ‘drop in’ replacement for oil fuels but which obviously has very different characteristics and lubrication needs.

All of the fuel types mentioned have little or no sulphur content and no other obvious components that would increase the acidity of the fuel so a very low BN lubricant would normally be needed. Another positive benefit is that they would also be very unlikely to contain any cat fines unless contaminated at some point during storage and delivery.

From the point of view of CO2 emissions, LNG performs best with ethane, propane and butane, each having one more carbon atom than its predecessor. The latter two are collectively referred to as LPG. As regards lubrication all have similar properties as LNG and can be considered as essentially the same.

Under most circumstances, if operating on one or more of the mentioned fuel types and even current ECA-compliant fuels, the lubricant should be either a 25 or 40BN product – although WinGD suggests that for LNG the BN could even be as low as 15. However, it should be borne in mind that the ship could also be running on other fuels at different times especially in the early days after the new global sulphur cap becomes effective.

By their very nature dual-fuel methanol engines are subject to an even wider range of sulphur conditions. As things stand, they could be burning 95% methanol, which has zero sulphur, along with either a low sulphur or high sulphur pilot fuel; they could be burning a 0.10% sulphur distillate fuel for ECA compliance; they could be burning up to a 3.5% maximum sulphur heavy fuel oil; or they could be burning a mix of 70% methanol along with either a high or low sulphur oil product.

Since none of the ships presently burning methanol has a scrubber fitted, they will be obliged to use another compliant alternative when not running on methanol, although it is entirely possible that if no compliant fuel is available then something else may have to be used instead. If that is the case, the cylinder lubricant will need to be changed for the duration of the voyage on non-compliant fuel and the again when reverting to compliant fuels.

It is entirely possible that the operators of some of the increasing number of ships now being fitted with scrubbers may in the future also decide that methanol is a good choice as a fuel. That would further complicate matters as to determining the best lubricant to use.

The range of potential fuel options for ships now able to use methanol already means that decisions are needed as to which level to limit the cylinder oil to the liners, and what the BN of the cylinder lubricant has to be.

Use of alternative fuels has so far been extremely limited and consequently kept under careful observation by the owners, engine makers and lubricant suppliers. Crews have therefore been well supported in managing lubrication changes and monitoring the effects of new fuels on the engine. If there is a wider take-up of alternative fuels, the crew involved may have less support and care should be taken to investigate requirements in conjunction with lubricant suppliers and manufacturers and whatever other sources of assistance are available.

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