The things they put in your Engine Oil

The things they put in your Engine Oil

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Despite being a tiny part of each litre of oil, additives are the most influential constituents which allow the oil to give proper lubrication and protection to an engine. Expensive and essential, they are the ‘secret recipe’ of an oil and work in various ways. Although the consumer often reads of the costly R&D efforts of large oil companies in formulating additive packages for new and better oils, much of the additive technology often comes from independent additive producers which agree to remain in the background. Of course, the final product (the new oil) is tested thoroughly by the oil company to ensure that it meets the targets set.

These targets will vary according to marketing strategies, with cost versus performance benefits being matched against the anticipated volume of oil to be sold. But whatever price the oil will be sold at, it must accomplish at least three general tasks: contaminant containment, heat removal and friction reduction. On its own, a base oil cannot achieve these in any significant way; in fact, various reactions arising from the combustion process will actually prevent the oil from functioning and will even alter its condition quickly. Which is why additives must be incorporated in today’s oils if the main tasks are to be carried out.

Today’s additives in lubricants are the result of complex technology, employing both organic and inorganic chemicals with 20% utilisation of the chemical elements. The most significant additives are those in lubricating oil which has its largest utilisation in internal combustion engines. Here, the additives have become an integral part of the lubricants as base oils alone, ie not compounded with additives, are no longer suitable for today’s engines with higher temperatures, higher speeds and higher pressures.

The exact composition of the additives in each oil is unique and a trade secret, so competition among additive producers is vigorous. Sometimes the oil companies may only be told part of the secret, but they are less concerned with the composition of the additive and more interested in how it can enhance the lubricating performance of their oil and allow them to make strong claims.

DEVELOPING ADDITIVES
Additive development has many routes; for example, when starting basic research, new technical requirements must be considered along with a cost/effectiveness optimisation for the additive. The rate of commercialisation of potential additives prepared in the laboratory may be low, but the overall cost of research to develop additives is extremely high.

Typically, an additive producer will discuss with the oil company what specifications are to be met. This is becoming a more complex matter as more and more specifications are being introduced by different organisations (including the US military) and motor manufacturers in North America, Europe and Japan.

Usually, an oil company will try to develop an oil which can meet as many of these specifications (the specification of the American Petroleum Institute or ‘API’ being the most familiar to motorists) as possible. Thus the number of tests (which are not cheap) needed has been proliferating at a rapid rate.

An important step in the development of an additive is the evaluation of the base oil. The source of crude oil and method of refining it must be known so that the additive can be properly tailored for incorporation.

After this evaluation is done in the laboratory, and satisfactory results are obtained, the fully compounded lubricant is then subjected to the necessary engine tests which are part of the specifications previously agreed on between the additive compounder and the oil company. Up to this stage, the expenditure is still low but it increases rapidly as test work begins and laborious engine tests have to be carried out.

Since it is very rare for a new lubricant formulation to meet the specifications immediately, the ‘recipe’ needs to be adjusted and retesting is needed until satisfactory results are obtained. And all the while, the frequent compatibility problems between additive components must be resolved, a job of ‘fine-tuning’ that is not only time-consuming but also very expensive.

TYPES OF ADDITIVES

While the composition of the additive is a trade secret, its function is widely publicised and if a comparison of additive functions is made among the various lubricants – engine oils, automatic transmission fluids, axle oils, hydraulic oils, gear oils, turbine oils and metalworking fluids – it will be found that many similarities exist.

For example, all lubricants now have anti-oxidants as well as anti-foam agents, and most have an anti-wear agents and rust-inhibitors. A common engine oil – this lubricant being the largest class of lubricants in the world – will have the following composition by weight:-

Base oil: 71.5 ~ 96.2%
Metallic detergent: 2 ~ 10%
Ashless dispersant: 1 ~ 9%
Zinc dithiophosphate: 0.5 ~ 3.0%
Antioxidant/antiwear: 0.1 ~ 2.0%
Friction modifiers: 0.1 ~ 3.0%
Antifoam: 2 ~ 15 parts/million
Pour point depressant: 0.1 ~ 1.5%

DETERGENTS
Detergents are metal-cleaning agents found in all engine oils. Besides providing anti-rust protection, they also assist in neutralisation of sulphur acids or oxy acids. The sulphur acids are formed when the sulphur compounds in the petrol oxidise to form sulphur oxides that combine with water (a by-product of combustion). They are particularly significant in diesel engines because diesel fuel can contain up to 4% sulphur. Oxy acids come from the oxidation of various lubricating base oil fragments.

DISPERSANTS
These are ashless, non-metallic cleaning agents with chemical structures similar to those of detergent additives. Usually, combinations of dispersant types are used in lubrication formulations.

A dispersant is needed to prevent all the by-products of combustion that drop into the oil from coming together to form large masses that would get stuck in the tiny oil passages. The additive also keeps all the particles in suspension, preventing them from accumulating in the bottom of the sump and not coming out with the oil during an oil change.

INHIBITORS
Inhibitors (often called the “anti” additives) are needed in engine oils, hydraulic oils and gear oils to prevent rust formation, and in automatic transmission fluids and axle oils to prevent corrosion. They also help in minimising oxidation, friction and foaming.

The oxidation inhibitors, which also have a role in preventing corrosion at the bearings, are an integral part of many lubricant additive compositions. These materials help to prevent the oxidative deterioration of the lubricant base fluid by scavenging free radicals produced by attack of oxygen. For protection against bearing corrosion, the additives form a protective film on the metallic surfaces in the engine, preventing attacks from acid.

Just as important are additives that prevent foaming in the oil, these most often being oil-insoluble chemicals in very low concentrations. They work by disrupting the liquid-air interface.

There are also additives that inhibit friction (also known as friction modifiers) and they come in many different types, either completely organic or of molybdenum compounds or suspended graphite.

ZINC DITHIOPHOSPHATES
These are the most important of the oxidation and bearing corrosion agents used in the formulation of lubricant additives. Zinc dithiophosphates (ZDP) help prevent valvetrain wear, in addition to minimising oxidation and bearing corrosion. They are the single most important chemicals used in formulations of engine oil additives.

POUR POINT DEPRESSANTS
These additives are more important in engine oils used in cold climates as they prevent the congealation of wax at low temperatures, causing the oil to thicken. In order to obtain lower pour points, the lubricating oil refiner removes the wax constituents, which solidify at relatively high temperatures, by a process known as known ‘dewaxing’. If the oil were completely dewaxed, it would reduce the yield of lube oil to an uneconomic level. In addition, complete dewaxing could also detract from some of the desirable lubricating oil characteristics.

In order to obviate the bad features of wax conglomeration, pour point depressants are most often used. They do not prevent the paraffin wax from crystallizing from the oil but are absorbed on the wax crystals. This absorption reduces the amount of oil included on the crystal, thus the reduction in the volume of the crystal permits easier flow of the lubricant.

VISCOSITY MODIFIERS
These are additives frequently publicised in advertisements for multigrade oils (eg SAE 10W-30, 15W-40, 0W-40, etc). These are oil-soluble organic polymers whose molecular weight may range from 50,000 to 150,000. What these additives do is to alter the ‘slope’ of the viscosity temperature relationship – an oil becomes viscous, or more fluid, as its temperature rises – so that it is more viscous at higher temperatures than would be the case without a viscosity modifier, while at the same time preventing the oil from becoming too thick at lower temperatures.

There are two general classes of viscosity modifiers: hydrocarbon types and ester types. Which type is used depends on the characteristics of the base oil to be treated, along with the type of multigrade oil to be produced. Not to be minimised in the selection of the viscosity modifier are the type of performance characteristics desired, the economics, and the viscosity shear stability that the final product must have.

ATF ADDITIVES
The additives required for an automatic transmission fluid (ATF) and axle oil need to be more specialised in function as the operating conditions are different from those experienced by engine oil. Different frictional properties are necessary for the many different types of automatic transmissions now produced.

With axle oils, the additive components are even more varied and specialised. To efficiently lubricate an axle, the oil must also offer extreme pressure protection and have a moderate anti-oxidation safeguard. Therefore, chemicals such as active sulphur compounds, chlorine containing compounds, and lead soaps are typically found in axle and gear oil additives.

TRENDS IN ADDITIVE TECHNOLOGY
For the future, new technical lubrication challenges exist as engine technology advances: the new generation of engines are smaller, run faster and have higher outputs. Special considerations must be given to such engines while at the same time making lubricant formulations that enhance fuel efficiency.

Turbocharged and supercharged engines are no longer uncommon nor limited to sportscars; even pick-ups have turbochargers with their diesel engines and turbodiesels are increasingly popular. Turbochargers run at extremely high temperatures and need oil that will not shear (break up) or vaporize under such conditions. Special additives are used to make it possible for even mineral-based oils to cope with such high temperatures, previously only possible with synthetic oils.

Then there are also the alternative-fuel engines that run on methanol or natural gas. Such fuels burn in a different manner from petrol or diesel and may need new types of additives to ensure proper lubrication and protection of the internal parts.

Finally, the ecological standpoint weighs heavily in any development of new oils. They must be compatible with engines that have emission control devices and not cause deterioration of the catalytic converters which are now commonplace with new vehicles. They should also have a certain degree of ‘environmental-friendliness’ to ensure facilitate disposal of used oil or recycling.

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