What Are Additives?

Additives are chemical products blended into base oils with the intention of:

• Improving the lubrication properties of oil over all operating conditions.
• Reinforcing and enhancing positive qualities of the base oil.
• Reducing or eradicating undesirable oil properties.

The overall purpose of oil additives is to modify the properties of lubricating oils so they protect vehicle engines under all operating conditions while reducing emissions and enhancing engine oil life. The percentage of additives in oil can vary from a few per cent to as high as 25per cent. Additive packages are carefully designed to ensure motor oils comply with the relevant API or ACEA specification and is suitable for use in all engines requiring oil to those specifications.

Chemicals used as additives include molybdenum compounds and fatty acids to reduce friction, phosphates and polysulphides as anti-wear agents, and antioxidants to prevent oil oxidation that results in deposits and thickening of the oil. Rust and corrosion inhibitors are used to prevent attack by organic acids present in oil and from acids produced as a result of combustion. Detergents, or soaps, made from metallic compounds of sodium, potassium, and calcium neutralize acids, and dispersants keep products of combustion and other contaminants in suspension, keeping engines clean.

Other additives improve the viscosity profile of oil so that as oil heats up, viscosity changes are minimized, ensuring good start-up lubrication as well as retaining sufficient viscosity to effectively lubricate engines when they are hot. These additives are long chain polymers and known as viscosity index improvers. A particular problem experienced in cold winter weather is that waxes in the oil crystallize and make it difficult or even impossible to pump engine oil, leading to engine failure. Pour point depressants are used to reduce the temperature at which waxes crystallize.

Oil Additive Groups

Oil additives can be grouped into three main groups in terms of their functions. There are additives that modify oil properties, protect the oil from external and aging effects, and shield engine surfaces from wear and damaging deposits. A fourth group covers miscellaneous issues such as seal performance.

The technical requirements of each additive group are dictated by the intended oil specification and the chosen base oil. High quality base oils generally require lower levels of additives, although conversely, more onerous engine requirements that have been introduced require the selection of both high quality base oils and advanced additive packs.

Another aspect that's important is that base oils derived from different crude oil stocks may contain distinctly different mixtures of hydrocarbons, requiring unique refining techniques and alterations to additive packs so blenders can manufacture lubrication oils to a particular specification.

Oil Modifier

An oil modifier is added to the oil so that it alters the oil properties to achieve certain qualities. The two primary oil modifiers are:

• Viscosity Index Improver: Possibly the most important property of oil is its viscosity. Oil should be sufficiently thin when it's cold to adequately lubricate a cold engine, yet retain sufficient viscosity to protect and lubricate the engine when it is hot. This is a particular issue with API Group I and II conventional base oils that have a low viscosity index. Viscosity index improvers modify the natural viscosity of oil. They are long chain polymers that, when cold, are coiled into a tiny ball and have little effect on the oil's viscosity. When heated, they open into a long molecule that thickens the oil, increasing its viscosity.
• Pour Point Improver: Most lubrication oils contain a small percentage of wax that's dissolved at normal temperatures. Once the oil cools below a certain temperature the wax crystallizes and the oil will not flow or pour. This is a problem in cold climates and pour point depressants are used to prevent wax crystals growing so oil will flow during very cold weather.

Oil Protection

 

As oil is used, it starts to chemically degrade. Also, under certain operating conditions, foam may form in the oil. Additives are used to reduce these effects:

• Antioxidants: Lubricating oil contains a range of hydrocarbons of different molecular lengths. When oil on the cylinder liners and in the cylinder head is heated by the combustion process, some of these products oxidize into a range of fatty products that form sludge, black asphaltic deposits, lacquers, and acidic compounds. The oxidation process is accelerated by a catalytic reaction with metal engine components. Antioxidants work by coating the metal surfaces, thus preventing or reducing oxidation.
• Anti-foaming Agents: Oil has a tendency to foam during high speed operation, leading to the formation of air bubbles in the oil. This causes oil cavitation, fluctuating oil pressure, and possible engine damage. A defoamant, often made from a silicon product, allows the air bubbles to escape from the oil and reduces foaming.

Surface Protection

Surface protection relates to the protection of engine surfaces where the primary lubrication method is through boundary lubrication. It also covers protection against corrosion and the avoidance of harmful deposits. The primary additives that protect engine surfaces include:

• Detergents: They have two functions. Firstly, as they are alkalis, they neutralize acids formed by oil degradation and during combustion and so prevent corrosion. Secondly, they ensure oxidation products are held in suspension preventing them from depositing on engine surfaces. Detergents are soaps based on metals such as calcium, sodium, and magnesium. Barium can be used but is generally avoided due to toxicity concerns.

• Dispersants: Dispersants also keep contaminants in suspension and due to a higher molecular weight are effective at preventing the deposition of heavier particles. They perform a cleaning function by preventing soot, varnish, lacquer, and other carbon-containing products of combustion from agglomerating into larger particles and separating out from the oil.

• Anti-wear additives: These additives protect heavily loaded engine parts from damage. When two components rub together, the heat produced causes anti-wear additives to decompose into a compound that coats the wear surfaces. This coating protects the underlying metal surfaces from damage. An excellent and commonly used anti-wear product is zinc dialkyldithiophosphates (ZDDP), although to some extent it has been replaced by ashless anti-wear additives due to a tendency to foul the catalyst in catalytic convertors.

• Extreme-pressure additives: These are similar to anti-wear additives but operate at higher temperatures on components where loads are very high. These additives have become extremely important as specific engine power has increased, leading to higher mechanical loads.

• Friction modifiers: These additives reduce friction between surfaces by forming a tough, low friction film that separates metal surfaces from the lubricating oil. Commonly used products are molybdenum compounds and long-chain fatty acids. They also reduce wear in low temperature areas where anti-wear agents are not effective.

• Corrosion inhibitors: These are products that are strongly attracted to metal surfaces. They form a durable, continuous film over metallic surfaces by a combination of chemical interaction and physical attraction. They are especially effective for the protection of bearing materials that are vulnerable to attack by organic acids and also protect steel and iron surfaces from rust caused by moisture or entrained water in the oil.

Seal Conditioner

One of the consequences of using highly refined API Group III oil or fully synthetic oil is these oils contain few if any aromatics. With API Group I and II oils, the levels of aromatics is higher, and they have a tendency to help seal materials to swell and stay soft. Synthetic oils include a seal conditioner additive to keep seals soft and in good condition.

Additive Packs

Additives are frequently prepared as a cocktail of active substances to blend base oil to a particular specification. They may also be supplied singly as required by the lube oil blender. The blending process requires careful control with the metering of exact quantities of the appropriate additives into the base oil. Some additives require pre-heating. Precise control is required to avoid contamination, and blending processes are frequently PLC controlled to ensure consistency.

When additives are supplied as packs, the blending process is simplified. The blending process may take some time as some additives need to be slowly added while the oil is agitated. After blending is complete, samples are taken for analysis to verify the blended oil is to the correct specification.

Additive packs are prepared with three specific objectives in mind: to control surface impact, improve the quality of the oil, and to protect oil from unwanted changes.

Surface Impact

A primary reason why modern vehicle engines last as long as they do is the quality of the lubricating oil additives, which minimize damage to engine surfaces. It's not unusual to hear of engines that have run for 250,000 miles (402,336 km) without being opened. Isuzu claims the design life for their diesel truck engines is 310,000 miles (498,897 km).

Surface impact additives play a major role in extending the life of an engine:

• Prevent deposits: Detergents ensure that waste products arising from oil oxidation and thermal degradation do not precipitate as varnish-like deposits on engine surfaces. They also prevent the precipitation of soot and other particles onto engine surfaces.

• Prevent sludge formation: Engine sludge forms when sufficient sludge particles agglomerate, allowing the sludge to fall out of the oil. Dispersants prevent this by associating with the sludge particles and keeping them in suspension. Over time, this leads to thickening of the motor oil, to the point that an oil change is required, but by preventing sludge formation, the additives ensure engine surfaces are clean and properly lubricated.

• Change friction characteristics to minimize wear: Anti-wear and extreme pressure additives are thermally sensitive, and when heavily loaded metal surfaces heat up, these products react and form a protective coating on these surfaces that reduces friction and prevents impact damage. This process ensures heavily loaded components such as valve stems, tappets, camshafts and other point-contact surfaces are not damaged or worn down.

Quality Improvement

Additives enhance the overall quality of base oil. They allow the use of cheaper base oils yet ensure the oil meets prescribed quality standards. Some quality enhancing aspects of the additive package are:

• Consistent lubrication film: Friction modifiers are attracted to metal surfaces, and this ensures these surfaces are always covered by a thin film of oil, which reduces friction and protects surfaces from wear.

• Flowability: It's important that oil flow is consistent and all parts of the engine receive adequate flow. One of the biggest challenges is to ensure that, in cold weather, oil does not form a gel and wax crystals that impede its flow. Pour point depressants lower the temperature at which this occurs so that during North American winters, oil retains its viscosity.

• Temperature resistance: This is achieved through the use of viscosity index modifiers that ensure the oil is neither too thin at high temperatures nor too thick at low temperatures; this is along with anti-wear and extreme pressure additives.

• Seal protection: Seal materials are prone to aging effects, especially from modern oils. Seal conditioners prevent this by softening the seals and are absorbed by seal material, causing the seal to swell slightly and seal more effectively.

Prevention Against Oil Degradation

As the automotive industry moves toward less frequent oil changes, so does the need to ensure that lubricating oil does not degrade between oil changes. When 3,000 mile oil change intervals were the norm, this was hardly an issue as long as the oil provided adequate engine protection. In addition to the use of better, longer lasting base oils, additives extend the service life of oil in several ways:

• Prevention of sludge formation: Sludge, formed from soot and the decomposition of acidic compounds that form in the oil over time, may block oil ways leading to oil starvation and reduced engine cooling. Detergents and dispersants prevent sludge forming by keeping soot and other deposits in solution in the oil.
• Prevent accelerated aging: As additives do their work, they are used up. In order for oil to be suitable for extended operation, additive packs need to contain sufficient additives to adequately cover the anticipated period between oil changes.
• Avoid engine corrosion: The metals used in engines are susceptible to corrosion unless protected. Rust and corrosion inhibitors coat metal surfaces and neutralize acidic compounds formed during combustion to prevent corrosion.
• Protect against moisture: Condensation of small amounts of water inside engines is unavoidable. Water contributes toward rust, sludge, oxidation, and oil foaming. Various additives protect engines from corrosion due to moisture and prevent sludge formation, oxidation, and foaming. These small quantities of moisture are usually evaporated when engines reach operating temperatures.

Multifunctional Aspect of Additives

Many additives perform more than one function. For example, some anti-wear products are extremely good antioxidants and corrosion inhibitors. There are viscosity index modifiers that have excellent dispersant and pour point depressant characteristics.

These interactions are taken into account during the design and testing of additive packages and are a reason behind the purchase of complete additive packages as opposed to the ad hoc application of individual additives.

Evolving Additive Technology

Additive technology is continually evolving to meet new requirements. Earlier API Group I base oils had high levels of aromatics, high sulfur content, and a low viscosity index, so additive packs for these oils were primarily focused on improving the viscosity index plus countering sludge formation through the use of detergents and dispersants.

API Group II oils have similar viscosity index ranges as Group I base oils with values that may vary between 80 and 120, but they differ in that they have lower quantities of sulfur and aromatics. Additive packs for these base oils include similar viscosity index improvers but do not need the same quantity of detergents and dispersants due to lower aromatic levels and lower sulfur levels that reduce emissions. Most current, high quality conventional lubrication oils are blended from API Group II oils. In order to meet the latest API SN / CJ-4 requirements, the additive packs have been upgraded to cater for higher engine loads, improved deposit protection, and more stringent sludge control.

API Group III oils are highly refined by severe hydrocracking and have particularly good and stable properties. These oils are considered to be synthetic oil due to their similarity to fully synthetic API Group IV PAO oils. They have a high viscosity index requiring fewer, if any, viscosity index improvers. These oils permit extended oil change intervals and are suitable for modern engines. They have negligible levels of aromatics and waxes and deteriorate slowly. Additive packs focus on ensuring long life, low sludge formation, deposit suspension, and anti-wear properties. These high quality oils together with appropriate additives also ensure low soot and ash production in diesel vehicles fitted with diesel particulate filters.

Additive Conflicts

ive technology is continually evolving to meet new requirements. Earlier API Group I base oil

One aspect of additive technology that manufacturers have to be careful about is conflict between different additives. Although this is unlikely to be an issue between various brands of commercially available motor oil, there have been examples when viscosity index modifiers contributed toward gel formation and several other issues with low temperature pumpability.

Lubrication oil blenders go to considerable lengths to ensure additive conflicts do not occur and adopt stringent quality control procedures. However, conflicts may occur when aftermarket additives are used, and care should be taken to monitor oil condition regularly to identify unusual signs such as sludge and thickening of the oil. This is not to say that aftermarket additives do not work, they do and are sold, not only by independent companies but by most major lubrication oil suppliers.

Future Additive Technology

Some interesting additive technology improvements demonstrate the continual developmental work conducted by additive and oil manufacturers as they continuously improve their products to meet modern requirements for better fuel economy, decreased emissions, and long oil life.

One development is the use of very thin lubricating oils in heavy vehicles. An example is the use of 0W-20 oil by Iveco, an Italian truck maker, that demonstrated a reduction of 0.44 per cent in fuel consumption at highway speeds and over 1 per cent at lower speeds.

There have been suggestions that nano technology may lead to significant improvements in the performance of some additives, although there appear to be few documented developments in this regard.

The growth in biodiesel production from fatty acid methyl ester (FAME) products, such as palm oil, soybean, and rapeseed, and the intention to increase the percentage of biodiesel in commercial diesel has raised concerns about the inherently reactive nature of FAME products, which tend to increase lubricant oxidation, corrosion, and the formation of deposits. Fortunately, it has been demonstrated that provided top tier API Group III and IV lubricating oils are used, the negative impact of high percentages of FAME biodiesel is low and manageable.