Blending for the Future

Richard Simpson explains how lubricant developments are advancing in parallel with engine technology

The standardisation of Euro 6 emissions control measures to include SCR and PM filtration, plus, for the majority of engine manufacturers, at least some exhaust gas recirculation, has increased demands on engine lubrication, but also has the potential to allow some fleets to rationalise the different grades of engine oils that they previously had to hold in stock.

For many decades, lubricant blenders providing oils for heavy-duty diesel engines have had to allow for an increasing burden of soot to be carried in suspension in the oil rather than being blown out in exhaust gas, and the introduction of Exhaust Gas Recirculation (EGR) has done nothing to decrease this requirement.

There’s also now an additional soot-related factor to take into account[wlm_nonmember][…]

[/wlm_nonmember][wlm_ismember]: which is maintaining the health of the exhaust system’s expensive and delicate particulate filter.

Old-school engine oil additives used by the producers and blenders contained relatively large quantities of phosphorous and sulphur as a cheap and effective means of boosting the lubricant’s Total Base Number (TBN is a relatively crude measure of the oil’s ability to neutralise contaminants). The phosphorous was included specifically for its anti-wear properties, also shared by sulphur, which in addition, contributed antioxidant qualities and aided engine cleanliness.

From around 2010, it was realised that these otherwise useful elements had the potential to form hard deposits on the ceramic and metallic particulate filters which were being introduced to the exhaust systems of heavy-duty diesels. These deposits, of sulphated ash as well as phosphorous and sulphur, were not cleared by the normal filter regeneration process which was initiated when the filter filled with carbon deposits. Instead, they could only be removed by taking the vehicle out of service and subjecting the filter element to mechanical cleaning. The delicate nature of the filter elements themselves means they can only withstand a limited number of cleans.

Depending upon the engine, and the type of particulate filter fitted, most modern bus and coach diesel engines will require either a Low or Mid-SAPS (Sulphated Ash, Phosphorous and Sulphur) oil. The growing number of PM-equipped buses and coaches on most fleets offers workshop managers the welcome opportunity to consolidate their engine oils to just one of two Low or Medium-SAPS types. These oils have different additive packages to conventional High-SAPS lubricants: with molybdenum, boron and calcium typically being used instead of phosphorous and sulphur.

Simply substituting one package of additives for another alone however, will not yield satisfactory performance from an oil.

There’s also the question of what the oil is made from, in terms of the base oil that is used not just to carry the additives – but also perform much of the lubrication, cooling and cleaning functions. In volume terms, about 75-80% of the contents of a drum of engine lube is base oil.

And this is where marketing tends to rear its ugly head. You will see various oils advertised as semi-synthetic, synthetic, and even full synthetic. You will even see oils for older engines being actively marketed as ‘mineral.’

Group terms

We’ll leave those terms aside for the moment, and go instead with the far more specific terms that the oil industry itself uses. It categorises base oils into Groups from I-V. Historically, most lubricants were made from Group I base oil. This was plentiful and easily produced from crude oil, being created from the so-called Vacuum Gas Oil (VGO, created by heating crude oil in a vacuum, where its boiling point is considerably reduced), which is one of the heavier streams of oil given off by crude in the refining process. Turning VGO into Group I base oil was a matter of washing out between 50 and 90% of the impurities with solvents, then removing paraffin waxes by cooling the oil to a point at which they solidified and were precipitated out.

The downside of Group I base oil was a high content of undesirable elements, including nitrogen, which impaired its lubrication qualities. Blenders traditionally compensated for this by using additives, or, more recently, diluting the Group I base oil with a quantity of higher quality Group III base oil.

But the move to Low and Mid-SAPS lubricants sounded a death knell for Group I based oils for modern diesel engines: it contains too much sulphur to be used to produce anything other than a High-SAPS lubricant.

While production of Group I base oils is a relatively simple process which was pretty much perfected in the 1920s, the current method for producing Group II and III base oils was only developed in the 1990s by Chevron. Besides producing finished lubricants in its own right, Chevron also supplies base oils to blenders worldwide from a plant opened in 2014 in Pascagoula, Missouri, USA.

Group II and III base oils are produced not as Group Is are by extracting impurities, but rather by using catalysts to change the oil’s molecules under pressure: this turns between 98 and 99.9% of impurities into high-quality base oil, which is visually as clear as water.

Group II base oils are typically a bi-product of petrol production while Group III base oils come from diesel production. Group II base oils are made from vacuum oil, while Group III base oils are produced directly from crude. Hence, markets which consume a lot of diesel, such as Europe, are likely to have refineries producing Group III base oils, while petrol-dominated markets like the USA tend to produce more Group II base oils.

There are important differences between the two, which relate directly to the viscosity of the finished lubricant. And viscosity is arguably the single most important characteristic of an engine or transmission lubricant. Group III base oils have a higher viscosity index than Group II base oils, beaning that they have a consistent viscosity over a wider temperature range. Chevron has produced what it calls a Group II+ base oil, which is made using the Group II production method, but approaches Group III performance in terms of viscosity index.

Group IV base oils are also what is known as synthetics. Rather than being produced directly from oil, it is made from ethene, which can be produced by steaming ethane and propane from natural gas and crude oil, by steaming naphtha from crude oil, or by the catalytic cracking of gas oil produced from crude oil.

Whatever process is used, the end result is a chemical called polyalphaolefin (PAO). A molecule of PAO consists of two carbon atoms, each with a pair of carbon atoms branching off it. The homogeneous molecular structure of PAO gives lubricants made using Group IV base oils a very consistent performance in varying conditions.

Like many technical advances, synthetic lubricants were developed out of necessity, originally having been a substitute for mineral and vegetable oils in Second World War aircraft engines. Engineers soon noticed that aircraft lubricated with synthetic oil were easier to start on cold mornings, and when their engines were overhauled there were no carbon deposits in their oil coolers. Synthetics, it emerged, could better cope with arduous conditions, especially extreme heat and cold, than conventional lubricants.

Group V is a bit of a catch-all term for all other synthetic base oils. These may be produced from diesters, polyolesters, alkylated benzenes, phosphate esters or other chemicals. Basically, all non PAO-derived synthetic base-oils are classified as Group V. For engine lubrication purposes, few are as suitable as Group IV base oils.

So, it must follow then that all lubricants sold as ‘synthetics’ must be made from Group IV or V base oils. Well, you’d think so, but you’d be wrong.

In various court cases around the world, it has been successfully argued that a lubricant labeled as synthetic can be made from a Group III base oil if its performance is similar to that of a lubricant made using a Group IV base oil. Likewise, a lubricant can contain a mixture of Group IV base oils and others, and still be described as a ‘synthetic’.

The result is some very muddy water for the end-user to swim in.

One oil blender markets a range of petrol engine lubricants which are variously labeled as ‘semi-synthetic’ (a blend of Group IV base oils and others) ‘synthetic’ (Group III base oil) and ‘full-synthetic’ (Group IV base oil), all at different price points.

The advantages of a genuine synthetic oil as an engine lubricant can be summarised as improved performance at low temperatures, improved performance and longer life at higher temperatures, wider multigrade performance (i.e. as a 5W-40 rather than a 10W-40), friction reduction, better natural detergency to remove deposits within the engine, and a greater molecular shear strength, meaning that individual molecules are not damaged leading to the oil thinning as it gets used.

There are few disadvantages, apart from cost, although seals in older engines may shrink or swell when exposed to synthetic oils which also may be incompatible with high-sulphur diesel of the kind which is no longer sold in the UK.

Standards

Unfortunately, there is no obligation upon oil blenders to declare just what base oil is used to produce individual lubricants, though scrutiny of the data sheets which they are obliged to provide on request, may yield a few clues.

Fleet engineers will do better if they take a step back from trying to outguess lubricant marketeers, and instead take guidance from engine manufacturers.
Automotive industry bodies in the USA and Europe have drawn up their own standards by which the suitability of various lubricants can be judged, and individual manufacturers also have their own approval standards.

In the USA, these standards are denoted by the initials SAE (Society of Automotive Engineers), and in Europe by the initials ACEA (Association of European Automotive Manufacturers). Additionally, the API (American Petroleum Institute) has its own sets of standards.

These standards are periodically reviewed, with new categories introduced to reflect the demands imposed on lubricants by advances in engine technology, and the demands of the end-user for fuel saving and extended oil drain intervals.

The ACEA standards are probably of the greatest relevance to the UK coach and bus operator, as most of the PCVs in operation here use engines designed and built in Europe.

ACEA’s standards, or sequences, as the body calls them, were introduced in 1996, and have since been updated in 1998, 1999, 2002, 2004, 2007, 2008, 2010, 2012, and then again at the end of last year.

Its heavy-duty engine sequences all have the prefix ‘E.’ They cover the lubricants’ ability to stay in grade over its drain interval, and control piston cleanliness, engine wear and ability to hold soot in suspension. They also indicate its suitability for engines featuring emissions-control systems such as EGR, SCR and particulate filters.

Some operators have been confused by the use of the letter E as a prefix, and mistakenly believe that an E4 lubricant is for Euro 4 engines, an E6 is for Euro 6 engines and so on. As the sequences are updated, obsolete ones are abandoned.

The current ACEA sequences are E4, for Euro 1-5 engines without particulate filters; E6, for Euro 1-6 engines including those using SCR, EGR and PM filters; E7, for Euro 1-5 engines without particulate filters, but where an extended oil drain is required; and E9, for Euro 1-6 engines with particulate filters where an extended oil drain interval is required.

The ACEA sequences provide a means by which end users can compare the suitability of various lubricants on offer. As one might expect from ACEA, they are based on requirements originally drawn up by Mercedes-Benz. However, it should be noted that all the heavy-duty engine manufacturers have their own standards – some, such as Iveco, have a tie with a specific oil company and others offer ‘own-label’ branded oil which is sold through their dealer network. If you have a coach on a dealer R&M contract, the chances are that it will be filled with either the manufacturer’s own-label lubricant or the brand to which the manufacturer is tied.

Care should be taken in matching manufacturer approvals to the actual vehicle in question. Most manufacturers approve both High-SAPS and Low-SAPS oils, for instance, with the latter being for vehicles fitted with particulate filters. Another way of confirming the correct oil is to use a ‘product finder’ website such as the one offered by Castrol: https://applications.castrol.com/oilselector/en_gb/c/search?vehicleType=trucks-and-buses-(-7-5t). Note that the function which enables you to identify your vehicle by its registration number does not work for heavy vehicles.

Click on the Alexander Dennis bar, and it shows the Enviro range from 2006 to 2014 only, so it is by no means as comprehensive as it might be, but it recommends Vectron Fuel Saver 5W-30 CJ-4 as lubricant for the Enviro’s Cummins ISB 6.7 engine.

This oil meets E6 and E9 standards and the API’s CJ-4. It also has Renault, Volvo, Caterpillar, Mack, and Deutz approvals.

The website also recommends three different types of transmission fluid, depending upon the manufacturer of the transmission fitted to the vehicle in question, and a choice of two different lubricants for the rear axle.

Obviously, care must be taken if the vehicle in question has been modified. For example, it’s likely that a bus retrofitted with a PM trap is going to require a Low or Medium SAPS engine oil, although this probably won’t be recommended for the bus as originally built.

Changing approaches

Extending the oil change period is a controversial subject, particularly in the UK where regular vehicle inspections are the norm, and many fleet engineers take the approach that ‘dropping the oil while she’s over the pit’ costs little but may save a lot. ACEA E7 and E9 oils are suitable for extended drain intervals, where the vehicle manufacturer allows. This is largely dependent upon the type of work the vehicle does. The engine lubricant is a coach that runs long-distances on European shuttles is far more likely to tolerate an extended drain interval than the oil in a city bus, for example.

Another point to watch is miss-filling when the engine is topped up between services. While anything is better than running an engine out of oil, diluting the correct oil with an incorrect one can have consequences. These might include a rise in fuel consumption if a non-fuel saver oil is used, a build-up of deposits if a High-SAPS oil is used in a vehicle with a PM filter, and a reduction in the efficacy of the lubricant if a lower-quality oil is used: for example, if a long-drain product is diluted with a standard one. In all these cases, consideration should be given to changing the oil ahead of schedule.

In any case, it is most unwise to push ‘long-drain’ oils beyond the recommended maximum distance. An engineer who had to work with a major truck manufacturer when it suffered a rash of engine failures on its Euro 5 products confided to CBW that: “When those full-synthetic oils are pushed too far beyond their change limit, there is no gradual decline in lubrication quality as you get with mineral oils – it just collapses, and major lubricant-related mechanical failures follow.”

Some fleets undertake oil sample analysis and use it to determine lubricant change intervals. A small sample of oil is taken out of the engine via the dipstick hole and sent away to a lab. There it is burned, and analysis of the flame colours can indicate the presence of contaminants either from within the engine (so-called wear metals such as copper, or large quantities of carbon) or external substances such as glycol or silicon. The former indicates a gasket or seal failure, the latter an air-filter problem.

A good oil analysis can not only indicate when an oil needs to be changed, but also if there is a more serious problem looming. Cheltenham-based Optimum Oils, for example, visits Go-Ahead bus depots to sample oils and examine components removed from vehicles in service for signs of premature wear and indications of potential component failure. It then schedules engine, transmission and axle lubricant services for individual vehicles, using a range of OEM approved lubricants.

Buses and coaches can remain in service for 10 to 15 years, often with the same operator. If a detailed approach to lubricant servicing can both stretch oil change intervals and reduce or eliminate the need to replace prematurely-worn units such as engines and gearboxes then that is surely an investment worth making.

Future

Future lubricant developments are likely to be driven by so-called ‘smart’ engine systems: for instance, oil pumps that deliver lubricant in quantities dictated by engine load rather than engine speed, and by ever-tightening emissions requirements. These are more likely to focus on reducing CO2 than NOx (although the USA plans tighter NOx limits from 2026), so more lubricant producers can be expected to follow Petronas down the ultra-low viscosity route, and also put more emphasis on friction reduction.[/wlm_ismember]