Low sulphur fuels, ECAs and cylinder lubrication

19 Sep 2014
Shell carries out comprehensive testbed trials on its research engines at its Hamburg Innovation Centre

Shell carries out comprehensive testbed trials on its research engines at its Hamburg Innovation Centre

The controversial question of which base number cylinder lubricant should be used in large two stroke engines is being turned on its head once again as oil suppliers and engine designers come to terms with the effects of using fuels of very low sulphur content.

Just as the industry was coming to terms with the need to use cylinder oils of very high base numbers in engines prone to cold corrosion, the oil majors are releasing oils with very low base numbers in response to the forthcoming ECA fuel sulphur legislation.

We spoke to Iain White, field marketing manager at ExxonMobil Marine Fuels & Lubricants about the upcoming changes and the things that ship operators should guard against. Mr White felt that, initially at least, a large majority would choose to run on MGO when in ECAs, and continue to use HFO for the majority of the time.

Both types of fuel are quite different in characteristics, and nothing is changing as far as what has become ‘normal’ operation is concerned. Ships burning HFO in two-stroke engines will continue to need a high base number oil, particularly when slow steaming. For newer-generation, slow-running, engines and earlier engines with modifications, cylinder oils of up to 100BN are recommended by the engine builders, while 70BN remains a standard for older engines, or conditions where cold corrosion is less likely to be problem.

Mr White said that ExxonMobil was helping shipowners meet the challenge with the introduction of ExxonMobil’s HDME50 low sulphur fuel, which offered compliance with ECA sulphur limits combined with the higher viscosity normally associated with residual fuels. Therefore onboard handling methods remain the same, avoiding many of the difficulties associated with fuel switching.

Although a universal cylinder oil was something of a holy grail in recent years, engine builders and oil suppliers mostly agree that a ‘one size fits all’ cylinder lubricant, able to cope with slow steaming as well as widely varying fuel sulphur levels is just not possible. Ships can run at very low engine load for much of the time, but are sometimes required to go at normal speed, so the oil has to cope with varying temperatures and moisture levels in the engine. And now that the same engines will be required to run reliably on fuels with sulphur content varying from 3.5% down to below 0.1%, the industry has come to accept that ships will have to switch cylinder oils as well as switching fuel.

The first oil supplier to announce a very low base number lubricant specifically for two-stroke engines running on ECA-compliant fuels was Shell Marine Products. Its Alexia S3 offers a 25BN rating, and Shell says that it will be made available in readiness for the 1 January 2015 deadline from ports within ECAs and major bunkering ports elsewhere, so ships planning to enter ECAs can have a supply on board.

Alexia S3 is formulated for use with low sulphur and distillate fuels up to 0.5% sulphur content, so is ready for the global sulphur limit expected to enter into force in 2020 or 2025, and likely to become the European limit from 2020.

"We are dedicated to providing our customers with the right solution, at the right place, at the right time," said Surinderdeep Singh, general manager of Shell Marine Products. “The introduction of Shell Alexia S3 completes our portfolio, ensuring all our customers will have the right lubricant suitable for their shipping needs.”

The very stringent 0.1% SOx restrictions will apply to the current ECAs, i.e. the Baltic Sea, the North Sea, North America and the US Caribbean Sea from 1 January 2015. Ships can avoid having to change fuel by fitting exhaust gas after-treatment plant – which is expensive and bulky – or converting to run on gaseous fuel such as liquefied natural gas (LNG). According to Shell, there have been discussions among regulators of further expansion of ECAs into the entire Atlantic seaboard of Europe, the Mediterranean Sea, coastal Korea, the Sea of Japan, the Australian coast, the shipping lanes of Singapore, Malaysia and Indonesia, and coastal China.

Almost simultaneously with the launch of Shell’s Alexia S3, French group Total Lubmarine introduced its Talusia LS 25 low alkaline lubricant specifically designed for slow speed two stroke engines running distillate fuels with 0.1% sulphur content.

Global marketing manager Serge Dal Farra said: “Talusia LS 25 is an innovative solution for ship operators looking for a reliable lubricant specifically designed to meet the challenging requirements of running engines, including the latest generation of crosshead two stroke engines, on distillate fuel. Talusia LS 25 will protect engines by offering excellent cleanliness thanks to its low-ash chemistry.”

Total already offers a 40BN lubricant for low sulphur residual fuels in its Talusia family, while the company clings to the ‘universal’ concept with its Talusia Universal, which it says is suitable for residual fuels with sulphur contents ranging between 0.5% and 3.5% in older-design engines. For modern engines affected by cold corrosion, it recommends Talusia Universal 100, the 100BN version, for neutralisation efficiency and reduced wear.

Mr Dal Farra added: “Shipping is a complex business with frequent changes to a vessel’s schedule, its fuels and cargoes. Total Lubmarine has an expert team that provides engine inspections, on-board and laboratory testing, training and advice.”

Castrol was one of the first suppliers to identify the cold corrosion issue and offer a high base number lubricant to control the problem. Its100BN oil is recommended for engines and operational conditions where cold corrosion is likely, i.e. newer and modified engines, and others running at low loads, while the company recommends its 70BN or 80BN lubricants for the mainstream. However, the company considers that its established Cyltech 40SX oil, of 40BN, is suitable for use under the new ECA limits.

Chevron Marine Products has launched its answer to the ECA regulations; for two-stroke engines this will be Taro Special HT LF. This is designed for two-stokes continuously operating on low sulphur distillate, to minimise wear and deposits throughout the combustion and exhaust areas. The new oil, of 25BN, has, says Chevron’s Rafael Teodoro, been extensively tested in both MAN and Wärtsilä engines, both showing significantly less deposit formation on the back of the piston ring pack, and fewer deposits in the piston ring grooves and lands, than occur when using a 40BN oil.

ExxonMobil too is bringing a 25BN cylinder lubricant to the market. Mobilgard 525 has been introduced to meet the challenges of lower sulphur fuels, not just in response to the ECA limits but to reflect the general trends in the industry. Mr White believes that 1.0% sulphur fuel will no longer be available at some point in the future. Shipowners will be faced with the choice of the current 3.5% maximum sulphur fuel, which can continue to be used by ships fitted with exhaust gas scrubbers even after the introduction of the 0.5% global sulphur cap, the naturally low sulphur heavy fuels resulting from refining of crude oils from areas such as South America, distillates, or what he describes as ‘hybrid’ fuels like ExxonMobil’s HDME50.

Even when using distillates, sulphur levels will not be consistent. MGO of 0.1% sulphur will be available in many places, but suppliers and producers are unlikely to lay on supplies at every bunker port; instead, automotive diesel type fuels will be provided. And as these can contain as little as 0.001% sulphur (10ppm), difficulties resulting from low sulphur levels are likely to be exacerbated.

Mr White says that very low BN cylinder oils are, in his opinion, essential when using fuels of 0.5% sulphur content and below in two-stroke marine diesel engines. The high base number oils contain additives that are essential to combat the natural acidity resulting from burning higher sulphur fuels, and these additives can perform other useful functions. Even though there is no need for alkaline formulations, the oil still has to perform a cleaning function.

Using oils of too high a base number will result in deposits. Even when the formulation includes additives intended to keep the top of the piston clean, deposits will still form around the rings and grooves, and a correctly formulated oil has to combine low base number and cleanliness – something that cannot currently be achieved with oils of 40BN or more, says Mr White.

So, all the major suppliers seem to be agreed that ships using two grades of fuel, inside and outside ECAs, will need to use two types of cylinder oil, and when switching fuel the engine room crews will have to switch cylinder oils too. Mr White of ExxonMobil regards fuel switching as fraught with potential danger – in comparison, changing cylinder oils seems easy. One major difficulty is the temperature variation when changing from hot HFO to cool gas oil – there can be as much as 100C difference between the two. In order to achieve a safe temperature gradient of less than 2C/min the fuel switching process can thus take about an hour. This is one of the problems that the company’s hybrid fuel is intended to reduce.

Mr White refers to the experience gained under the California Air Resources Board regulations in the US, where some 60 ships per year have been known to suffer power loss due to fuel switching problems. He suggests that the possible consequences of vessels losing power at, say, the western entry into the English Channel ECA, just as they are changing fuel, could be severe. “Owners will need to focus on operational best practice,” he said. “For many of them, they are entering uncharted territory.”

ExxonMobil’s experience so far suggests that even a short time in an ECA using an oil of too high a base number can result in rapid and unacceptable levels of deposits forming. If the time in the ECA can be measured in hours rather than days, it may be possible to avoid changing oil, says Mr White, but for longer periods the oil must be switched, he says – and this is backed up by the engine builders’ recommendations.

Another point of universal agreement among the oil suppliers is the desirability of monitoring oil conditions. Several, including ExxonMobil and Chevron, offer on-board test kits that can detect both liner wear and corrosive ferrous particles. As well as confirming the correct choice of lubricant, such testing can be invaluable in setting feed rates – too low a feed results in excessive wear, while too high a rate is both wasteful and can promote deposit formation. Mr White suggests that early-on in the process samples are sent to the company’s test laboratories, which will provide a check on procedures and onboard skill levels, then once the crew is comfortable with the test routine, scrape down samples should be tested onboard every 250h, or at every fuel change, backed up by a lab sample from each voyage.

He says that owners are facing having to manage large and frequent shifts in maintenance requirements – but the oil companies will help out whenever possible.

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