The knock-on effects for lubricants vary for different engine types and will depend on the steps that owners take to meet emissions caps. The biggest changes will be for low-speed engines, which are used in large cargo ships. Most suppliers have introduced new cylinder oils for low-speed engines burning low-sulfur fuels, though it is hotly debated whether a single universal grade, or a range of grades to suit different situations, is better. In the future, many engines may require new cylinder oil technology that will entail significant time and expense to develop. Fortunately, the industry has a few years breathing space to find solutions.

Regulating Emissions

The key regulations governing shipping emissions were developed by the united Nations International Maritime Organization and are set out in Annex VI to IMOs MAR-POL, the International Convention for the Prevention of Pollution from Ships. The emission limits first introduced in 2005 were not particularly demanding, but tighter limits were adopted in 2008 and phased in beginning in 2010.

Annex VI sets global caps on emissions of nitrogen oxides and sulfur oxides, with tighter limits applying in Emission Control Areas. The Baltic Sea and the North Sea and English Channel are designated as SOx ECAs, and North American waters out to 200 nautical miles from most of the united States and Canada coastline is an ECA for both NOx and SOx. A NOx and Sox ECA around Puerto Rico and the u.S. Virgin Islands in the Caribbean comes into effect in 2013, with sulfur restrictions applying from 2014. Additional ECA proposals are under consideration, but none has yet been submitted formally to IMO.

Supplementing IMO regulations are some regional rules, notably for the European union and California. These are generally aligned with IMO, but impose additional requirements or shorter timelines.

IMOs NOx emission limits generally apply only to new ships. A global Tier I cap applies to ships built during or after 2000, with retrospective application to some post-1990 ships. A tighter Tier II cap applies to ships built from 2011. Most engines supplied since 2000 meet the relevant limits by means of in-engine changes to fuel injection and valve timing.

A Tier III limit will apply within NOx ECAs to ships built from 2016. The Tier III limit is 80 percent below Tier II, far lower than can be achieved by engine modifications alone. Currently the most favored approach to meet Tier III is to remove NOx from the exhaust using selective catalytic reduction. Other technologies such as exhaust gas recirculation show promise, and various techniques for injecting water into the combustion process may play a supplementary role.

Although automotive experience shows SCR catalysts can be damaged by lubricant ash, this is less of a problem in marine applications. Marine SCR uses different catalysts, often designed to withstand the high ash burden from operating on residual fuels. Nonetheless some engine builders suggest as a precaution that engines fitted with SCR should use lubricant with the lowest Base Number consistent with the fuel sulfur content to minimize any adverse effects on SCR catalyst.

Techniques such as EGR or water injection will change conditions in the combustion chamber, altering stresses on the lubricant. Whether this creates a need for improved lubricants will emerge only as experience is built up.

Limits on Sox

IMOs current fuel sulfur limit of 1.00 percent within ECAs will be lowered to 0.10 percent in January 2015. The global fuel sulfur cap will be lowered from the current 3.50 percent to 0.50 percent in 2020, but the change may be deferred to 2025 if there are concerns about fuel availability.

Non-IMO regulations introduce additional requirements. In all Eu ports, ships at berth must use fuel with sulfur content of 0.10 percent or less. The Eu will introduce the 0.50 percent fuel sulfur limit in 2020, even if IMO defers it until 2025. Ships calling at California ports must use distillate low-sulfur fuel (1.0 percent or 0.5 percent sulfur depending on grade), with the limit being lowered to 0.1 percent in January 2014.

At present, over 75 percent of fuel used by international shipping is residual fuel oil. RFO is a black, high-viscosity oil blended from residues of refining processes, and on average it contains 2.6 percent sulfur. It is most unlikely that refiners will invest in residue desulfurisation to convert this to low-sulfur RFO, given the economics and technical limitations of the process. Therefore the only fuels produced in sufficient quantities to meet the 2015 sulfur limit of 0.10 percent, or the 2020/2025 limit of 0.50 percent, will be distillate fuels broadly similar to land-based diesel or domestic heating oil. Distillate fuel today typically costs at least u.S. $300 (230) per metric ton more than RFO. A complete switch from RFO to distillate by 2020 would increase shippings fuel costs by roughly $100 billion per year.

An alternative fuel receiving much attention is liquefied natural gas, which has the benefit of generating low levels of emissions. Depending on engine design and operation, SOx can be very low or zero, and NOx can be 25 percent to 90 percent lower than for RFO. Other emissions that may come under scrutiny in future, such as carbon dioxide or particulate black carbon, are also lower with LNG.

LNG has other advantages. It should be cheaper to deliver onboard than distillate fuel even after allowance for higher delivery costs, and it may even be competitive with RFO. LNGs long-term supply outlook is better than conventional petroleums, and it is well-proven as a bunker fuel, at least in some engine types. There are 100 gas carriers in service or on order that burn boil-off from their LNG cargo in dual-fuel diesel engines, and about 30 small coastal ships in Norway that operate exclusively on LNG. Although an LNG-fueled ship will cost several million dollars more than a conventional one, the economics can be attractive. Obstacles to wider adoption of LNG bunkering, such as limited supply infrastructure and lack of globally recognized standards, are being addressed.

Exhaust gas scrubbers are permitted by IMO and the Eu as an alternative to burning low-sulfur fuels. Commercially available scrubbers that use seawater or recirculating sodium hydroxide solution to capture SOx can reduce emissions by 95 percent or more. A scrubber typically costs a few million dollars, but savings from using high-sulfur RFO instead of 1 percent sulfur RFO (possible until 2015) or distillate can repay investment. For a ship trading mostly within ECAs after 2015, payback time can be less than a year. However, fewer than 30 ships currently operate with scrubbers. Reasons for the low uptake might include reluctance of ship owners to invest ahead of the 2015 lowered ECA limit and perceptions that the technology is not yet sufficiently proven.

Scenarios for Compliance

Until 2015, it is likely that the vast majority of ships will comply with IMO regulations by switching to 1 percent sulfur fuel in ECAs. Starting in 2015, the much higher cost of ECA-compliant distillate fuel will make alternatives more attractive. Installation of scrubbers will accelerate, and LNG bunkering will expand, particularly for short-sea shipping within ECAs. Beginning in 2020 or 2025, ships that formerly burned RFO will have to use distillate at all times unless they are fitted with scrubbers or can operate on LNG. The high cost of distillate is likely to drive widespread adoption of scrubbers. LNG may make inroads as fuel for deep-sea shipping provided its pricing remains attractive and supply infrastructure has expanded.

Ships with scrubbers will continue to use high-sulfur RFO, and for them there will be no change in lubrication requirements. Ships that switch to low-sulfur fuel may see changes.

One key function of a marine diesel engine lubricant is to control corrosive wear by neutralizing acids produced during combustion from sulfur in the fuel. Engine lubricants contain alkaline additives for neutralization, with the amount of alkalinity indicated by the lubricants base number, or BN.

Different engine types call for different BN. Medium-speed four-stroke engines (which are typically used for electricity generation onboard, and for main propulsion in passenger ships and smaller cargo ships) generally require 30 to 55 BN lubricant when burning high-sulfur RFO. Low-speed two-stroke engines (used for main propulsion in large container ships, tankers and bulkers) have commonly used 70 BN cylinder oil when burning high-sulfur RFO.

For medium-speed engines, there is generally no need to change lubricant when alternating between high-sulfur and low-sulfur fuels. If a permanent switch from RFO to distillate is made, operators should consider draining the lubricant from the engine and replacing it with a low BN lubricant designed for distillate operation. There is extensive experience operating medium-speed engines on distillates, and well-proven lubricants are commercially available.

Medium-speed engines operating on LNG (either exclusively or as dual-fuel engines) do not present new lubrication challenges either. There is extensive experience with LNG operation, and proven lubricants are commercially available.

For low-speed engines new lubricants may be required, as it can become important to match lubricant BN to fuel sulfur. If BN is too high, unneutralized additive can form hard calcium carbonate deposits on the piston crown land and in the ring pack. These deposits can disrupt the oil film, leading to serious problems such as excessive wear, liner polishing or scuffing, or ring breakages. When switching from high-sulfur RFO to low-sulfur fuel, BN through-put must be matched to fuel sulfur. Matching can be achieved to some extent by adjusting cylinder oil feed rate but a lower BN cylinder oil may still be needed.

When ECAs first came into effect, engine designers advised it was unnecessary to switch from 70 BN cylinder oil if low-sulfur fuel was used for less than one or two weeks at a time. For longer periods on fuel with sulfur below 1 percent, they recommended switching to a properly formulated 40 or 50 BN cylinder oil during low-sulfur operation if engine inspection confirmed the need.

Debating universal OilsMore recently, several lubricant marketers have introduced universal cylinder oils with BN in the range of 55 to 60, claiming that they are suitable for operation on fuels with sulfur content as low as 0.5 percent or 1 percent and as high as 3.5 percent or more. However, not all lubricant suppliers advocate their use, and leading engine designer MAN Diesel and Turbo recently said it cannot recommend 50 to 60 BN cylinder oils for its latest-generation engines using higher-sulfur fuel.

Use of distillate fuel or LNG in low-speed engines may call for new lubricants. Operation on distillate fuel, particularly long-term, may require cylinder oils of lower BN and different formulations than those used with RFO. To date there has been little experience operating low-speed marine engines for prolonged periods on distillate fuel, and so there is little basis for judgments about optimum lubricant formulation.

The industry has a similar lack of experience lubricating low-speed engines running solely on LNG. A number of factors could influence lubrication requirements under such circumstances:

the virtually zero sulfur content of LNG;

engine design features such as whether gas is injected at low or high pressure;

operational factors such as the type and amount of pilot fuel used for ignition;

the split between LNG and conventional fuel in dual-fuel operation.

There are very few demonstration LNG engines operating or under construction and no low-speed engines in commercial service operating on LNG. Thus opportunities for in-service testing of candidate lubricants are limited, which may slow the development of cylinder oils optimized for LNG operation. It is fortunate that significant demand for such oils appears to be a few years off, because product development and in-service testing can take several years.