Lubricant Additives - A Practical Guide

Lubricant Additives – A Practical Guide

Lubrication professionals are often very familiar with the base oil viscosity of their lubricants. After all, viscosity is the most important property of a base oil.

The baseline for lubricant feed is set and its health is monitored based on viscosity alone. However, there is more to lubricants than just viscosity. Understanding the role of additives and their function in lubricants is critical.

Lubricant additives are solid organic or inorganic compounds dissolved or suspended in the oil. Additive levels are typically between 0.1% and 30% of the oil volume, depending on the machine.

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Additives have three basic roles:

Enhance the performance of existing base oils with antioxidants, corrosion inhibitors, antifoaming agents, and demulsifiers.

Suppress undesirable base oil properties with pour point depressants and viscosity index (VI) improvers.

Give base oils new properties with extreme pressure (EP) additives, detergents, metal deactivators, and binders.

Polar Additives
Additive polarity is defined as the natural directional attraction of additive molecules to other polar substances that come into contact with the oil. In simple terms, it is anything that water can dissolve or dissolve in water.

Sponges, metal surfaces, dirt, water, and wood pulp are examples of polar materials. Non-polar materials include wax, Teflon, mineral base oils, duck backs, and water repellents.

It is important to note that additives are also depletable. Once they are gone, they are gone. Think about the environment you work in, the products you produce, and the types of contaminants.

These are all around you every day. If you allow contaminants that additives tend to absorb (such as dirt, silica, and water) into your system, the additives will stick to the contaminants and settle to the bottom or be filtered out, thus depleting your additive package.

Polar Mechanisms
There are a few polar mechanisms worth discussing, such as particle encapsulation, water emulsification, and metal wetting.

Particle encapsulation is when additives attach to the surface of a particle and encapsulate it. This category of additives includes metal passivators, detergents, and dispersants. They are used to peptize (disperse) soot particles to prevent them from agglomerating, settling, and settling, especially at low to moderate temperatures.

You will often see this in engines. This is a good reason to fix and eliminate problems as soon as they are detected with a proper oil analysis test panel.

Water emulsification occurs when the polar head of an additive attaches to microscopic water droplets. Such additives are emulsifiers. Think about this the next time you observe water in a reservoir.

While it is critical to remove the water, determine where it entered the system, and fix it with a root cause maintenance approach, you must also remember that the additive package has been compromised. In lubrication terms, this is called additive depletion. A proper oil analysis report can determine the health of the remaining additives in the lubricant.

Metal wetting is when additives anchor to metal surfaces, which is exactly what they are supposed to do. They attach to the inside of a gearbox, gear teeth, bearings, shafts, and more.

Additives that perform this function are rust inhibitors, anti-wear (AW) and EP additives, oiliness agents, and corrosion inhibitors.

AW additives are specifically designed to protect metal surfaces under boundary conditions. They form a ductile, ash-like film at moderate to high contact temperatures (75 to 100 degrees Celsius).

At boundary conditions, the AW film shears in place of the surface material.

A common anti-wear additive is zinc dialkyl dithiophosphate (ZDDP). It reduces the risk of metal-to-metal contact, which can cause heating, oxidation, and negatively affect film strength.

Additives play an important role in machinery lubrication, whether they enhance, inhibit, or impart new properties to the base oil. Remember, once an additive is used, it is gone, so don't forget to check your additive package.

Types of Lubricant Additives

There are many types of chemical additives that are blended into base oils to enhance the properties of the base oil, inhibit some of the base oil's undesirable properties, and possibly impart some new properties.

Additives typically make up anywhere from 0.1% to 30% of the finished lubricant, depending on the intended use of the lubricant.

Lubricant additives are expensive chemicals, and formulating the right additive package or formulation is a very complex science. Additive selection makes the difference between a turbine oil (R&O) and a hydraulic oil, gear oil, and engine oil.

There are many types of lubricant additives, and selection is primarily based on their intended efficacy. Additives are also selected based on their miscibility with the chosen base oil, compatibility with other additives in the formulation, and cost-effectiveness.

Some additives work within the oil (e.g., antioxidants), while others work on the metal surface (e.g., anti-wear additives and rust inhibitors).

General Lubricant Additives
These general types of additives include:

Antioxidants
Oxidation is the general attack of oxygen in the air on the weakest components of the base oil. Oxidation occurs at any temperature, but is accelerated at higher temperatures and in the presence of water, wear metals, and other contaminants.

It ultimately leads to the formation of acids (which cause corrosion) and sludge (which causes surface deposits and increased viscosity). Antioxidants (also called antioxidants) are used to extend the life of the oil.

They are sacrificial additives that are consumed in the process of slowing down the oxidation reaction, thereby protecting the base oil. They are found in nearly all lubricating oils and greases.

Rust and Corrosion Inhibitors
These additives reduce or eliminate internal rust and corrosion by neutralizing acids and forming a protective chemical barrier that repels water from the metal surface. Some corrosion inhibitors are specifically designed to protect certain metals. Therefore, one oil may contain more than one. They are found in almost all oils and greases. Metal deactivators are another type of corrosion inhibitor.

Viscosity Index Improvers
Viscosity index improvers are very large polymer additives that partially prevent the oil from thinning (losing viscosity) as the temperature rises. This type of additive is widely used when blending multigrade oils (such as SAE 5W-30 or SAE 15W-40).

They also improve the flow of the oil at low temperatures, which reduces wear and improves fuel economy. In addition, viscosity index improvers are used to obtain high viscosity index hydraulic and gear oils to improve starting and lubrication properties at low temperatures.

To visualize how a viscosity index improver works, think of the viscosity index improver as an octopus or coil spring that stays rolled up into a ball at low temperatures and has little effect on the viscosity of the oil.

Then, as the temperature rises, the additive (or octopus) expands or extends its arms (making it larger) and prevents the oil from becoming too thin at high temperatures. VI improvers do have some disadvantages. These additives are large polymers (high molecular weight), which makes them easily shredded or cut into small pieces by machine parts (shear forces). Gears are known to wear VI improvers very badly.

The permanent shearing action of VI improvers can cause significant viscosity loss, which can be detected by oil analysis. The second form of viscosity loss is due to high shear forces in the load zone of friction surfaces (such as journal bearings).

It is believed that the VI improver loses its shape or uniform orientation, thus losing some of its thickening ability.

The viscosity of the oil temporarily drops in the load zone and rebounds to normal viscosity after leaving the load zone. This characteristic actually helps reduce oil consumption.

VI improvers come in a variety of types (olefin copolymers are common). High-quality VI improvers are less susceptible to permanent shear loss than low-cost, low-quality VI improvers.

Antiwear Additives (AW)

These additives are typically used to protect machine parts from wear and metal loss under boundary lubrication conditions. They are polar additives that adhere to the friction metal surfaces. They react chemically with metal surfaces when metal contacts are made under mixed and boundary lubrication conditions. They are activated by the contact heat and form a film that minimizes wear. They also protect the base oil from oxidation and protect the metal from damage by corrosive acids. After these additives have performed their function, they are "consumed" and adhesive wear damage can then increase. They are usually phosphorus compounds, the most common being zinc dialkyl dithiophosphate (ZDDP).

ZDDP is available in a variety of versions - some for hydraulic applications and others for the high temperatures encountered in engine oils. ZDDP also has some antioxidant and corrosion protection properties. In addition, other types of phosphorus-based chemicals (e.g. TCP) are also used for wear protection. Extreme Pressure (EP) Additives These additives are more chemically aggressive than AW additives. They react chemically with metal (iron) surfaces and form a sacrificial surface film that prevents welding and seizure of relatively rough surfaces caused by metal-to-metal contact (adhesive wear). They are activated under high loads and the resulting high contact temperatures. They are commonly used in gear oils, giving them a distinctive and strong sulfur smell. These additives usually contain sulfur and phosphorus compounds (and occasionally boron compounds).

They are corrosive to brass, especially at high temperatures, and should not be used in worm gears and similar applications where copper-based metals are used. Although there are some CP additives that contain chlorine, they are rarely used due to corrosion issues.

Antiwear additives and EP additives are a large class of chemical additives that function to protect metal surfaces during boundary lubrication by forming a protective film or barrier on the worn surfaces.

As long as a hydrodynamic or elastohydrodynamic film of oil is maintained between metal surfaces, boundary lubrication does not occur and these boundary lubrication additives are not needed to perform their function.

When the oil film is broken and asperity contact occurs under high loads or high temperatures, these boundary lubrication additives protect the worn surfaces.

Detergents
Detergents have two functions: first, they help keep hot metal parts clean and free of deposits, and second, they neutralize acidic substances formed in the oil. Detergents are primarily used in engine oils and are alkaline in nature.

They form the basis of the reserve alkalinity of engine oils, which is referred to as the base number (BN). They are typically materials of calcium and magnesium chemistry. Barium-based detergents were used in the past but are rarely used now.

Since these metal compounds leave an ash deposit when the oil is burned, they may cause unwanted residue to form in high-temperature applications. Due to this ash concern, many OEMs are specifying low-ash oils for equipment operating at high temperatures. A detergent additive is normally used in conjunction with a dispersant additive.

Dispersants

Dispersants are mainly found in engine oil with detergents to help keep engines clean and free of deposits. The main function of dispersants is to keep particles of diesel engine soot finely dispersed or suspended in the oil (less than 1 micron in size).

The objective is to keep the contaminant suspended and not allow it to agglomerate in the oil so that it will minimize damage and can be carried out of the engine during an oil change. Dispersants are generally organic and ashless. As such, they are not easily detectable with conventional oil analysis.

The combination of detergent/dispersant additives allows more acid compounds to be neutralized and more contaminant particles to stay suspended. As these additives perform their functions of neutralizing acids and suspending contaminants, they will eventually exceed their capacity, which will necessitate an oil change.

Anti-foaming Agents

The chemicals in this additive group possess low interfacial tension, which weakens the oil bubble wall and allows the foam bubbles to burst more readily. They have an indirect effect on oxidation by reducing the amount of air-oil contact.

Some of these additives are oil-insoluble silicone materials that are not dissolved but rather dispersed finely in the lubricating oil. Very low concentrations are usually required. If too much anti-foaming additive is added, it can have a reverse effect and promote further foaming and air entrainment.

Friction Modifiers

Friction modifiers are typically used in engine oils and automatic transmission fluids to alter the friction between engine and transmission components. In engines, the emphasis is on lowering friction to improve fuel economy.

In transmissions, the focus is on improving the engagement of the clutch materials. Friction modifiers can be thought of as anti-wear additives for lower loads that are not activated by contact temperatures.

Pour Point Depressants

The pour point of an oil is approximately the lowest temperature at which an oil will remain fluid. Wax crystals that form in paraffinic mineral oils crystallize (become solid) at low temperatures. The solid crystals form a lattice network that inhibits the remaining liquid oil from flowing.

The additives in this group reduce the size of the wax crystals in the oil and their interaction with each other, allowing the oil to continue to flow at low temperatures.

Demulsifiers

Demulsifier additives prevent the formation of a stable oil-water mixture or an emulsion by changing the interfacial tension of the oil so that water will coalesce and separate more readily from the oil. This is an important characteristic for lubricants exposed to steam or water so that free water can settle out and be easily drained off at a reservoir.

Emulsifiers

Emulsifiers are used in oil-water-based metal-working fluids and fire-resistant fluids to help create a stable oil-water emulsion. The emulsifier additive can be thought of as a glue binding the oil and water together, because normally they would like to separate from each other due to interfacial tension and differences in specific gravity.

Biocides

Biocides are often added to water-based lubricants to control the growth of bacteria.

Tackifiers

Tackifiers are stringy materials used in some oils and greases to prevent the lubricant from flinging off the metal surface during rotational movement.

To be acceptable to blenders and end users alike, the additives must be capable of being handled in conventional blending equipment, stable in storage, free of offensive odor and be non‑toxic by normal industrial standards.

Since many are highly viscous materials, they are generally sold to the oil formulator as concentrated solutions in a base oil carrier.

A couple of key points about additives:
More additive is not always better. The old saying, “If a little bit of something is good, then more of the same is better,” is not necessarily true when using oil additives.

As more additive is blended into the oil, sometimes there isn’t any more benefit gained, and at times the performance actually deteriorates. In other cases, the performance of the additive doesn’t improve, but the duration of service does improve.

Increasing the percentage of a certain additive may improve one property of an oil while at the same time degrade another. When the specified concentrations of additives become unbalanced, overall oil quality can be affected.

Some additives compete with each other for the same space on a metal surface. If a high concentration of an anti-wear agent is added to the oil, the corrosion inhibitor may become less effective. The result may be an increase in corrosion-related problems.

How Oil Additives Get Depleted

It is very important to understand that most of these additives get consumed and depleted by:

“decomposition” or breakdown,
“adsorption” onto metal, particle and water surfaces, and
“separation” due to settling or filtration.

The adsorption and separation mechanisms involve mass transfer or physical movement of the additive.

For many additives, the longer the oil remains in service, the less effective the remaining additive package is in protecting the equipment.

When the additive package weakens, viscosity increases, sludge begins to form, corrosive acids start to attack bearings and metal surfaces, and/or wear begins to increase. If oils of low quality are used, the point at which these problems begin will occur much sooner.

It is for these reasons that top-quality lubricants meeting the correct industry specifications (e.g., API engine service classifications) should always be selected. The following table can be used as a guide for a more thorough understanding of additive types and their functions in engine oil formulations.

It is evident from the information above that there is a lot of chemistry occurring in most of the oils that are used to lubricate equipment. They are complicated mixtures of chemicals that are in balance with one another and need to be respected.

It is for those reasons that the mixing of different oils and adding additional lubricant additives should be avoided.

After-market Additives and Supplemental Oil Conditioners

There are hundreds of chemical additives and supplemental lubricant conditioners available. In certain specialized applications or industries, these additives may have a place in the improvement of lubrication.

However, some manufacturers of supplemental lubricants will make claims about their products that are exaggerated and/or unproven, or they fail to mention a negative side effect that the additive may cause.

Take great care in the selection and application of these products, or better still, avoid using them. If you want a better oil, buy a better oil in the first place and leave the chemistry to the people who know what they are doing.

Often oil and equipment warranties are voided with the use of after-market additives because the final formulation has never been tested and approved. Buyer beware.

When considering the use of an after-market additive to solve a problem, it is wise to remember the following rules:

Rule #1
An inferior lubricant cannot be converted into a premium product simply by the inclusion of an additive. Purchasing a poor-quality finished oil and attempting to overcome its poor lubricating qualities with some special additive is illogical.

Rule #2
Some laboratory tests can be tricked into providing a positive result. Some additives can trick a given test into providing a passing result. Often multiple oxidation and wear tests are run to obtain a better indication of the performance of an additive. Then actual field trials are performed.

RULE #3
Base oils can only dissolve (carry) a certain amount of additive. As a result, the addition of a supplemental additive into an oil having a low level of solubility or being already saturated with additive may simply mean that the additive will settle out of the solution and remain in the bottom of the crankcase or sump. The additive may never carry out its claimed or intended function.

If you choose to use an after-market additive, before adding any supplemental additive or oil conditioner to a lubricated system, take the following precautions:

Determine whether an actual lubrication problem exists. For instance, an oil contamination problem is most often related to poor maintenance or inadequate filtration and not necessarily poor lubrication or poor-quality oil.
Choose the right supplemental additive or oil conditioner. This means taking the time to research the makeup and compatibility of the various products on the market.
Insist that factual field-test data is made available that substantiates the claims made regarding the product’s effectiveness.
Consult a reputable, independent oil analysis laboratory. Have the existing oil analyzed at least twice before adding a supplemental additive. This will establish a reference point.
After the addition of the special additive or conditioner, continue to have the oil analyzed on a regular basis. Only through this method of comparison can objective data regarding the effectiveness of the additive be obtained.

There is a great deal of controversy surrounding the application of supplemental additives. However, it is true that certain supplemental lubricant additives will reduce or eliminate friction in some applications such as machine tool ways, extreme pressure gear drives and certain high-pressure hydraulic system applications.

For how long will ashless dispersant aviation engine oils be around?

When asked for an example of an air-cooled engine, many people will mention the Porsche 911 Carrera, known for its top-of-the-line air-cooled flat-six engine, the so-called ‘Boxer’ engine. Known by many as the ‘air-cooled 911s’, the final iteration of Porsche’s flat-six air-cooled engine was discontinued after the 1998 model year in favor of a water-cooled engine. It is among the last consumer automobiles to be produced with an air-cooled engine.1, 2

In contrast the aviation industry uses a mix of both air- and water-cooled engines, even favoring the air-cooled option in the case of aircraft piston engines. This preferred cooling method by the aviation industry hints at the reason behind the ubiquity of ashless dispersants in aviation engine oils.

Castor oil was the oil of choice for aircraft oils at the beginning of the aviation era because of their good lubricity. These oils were dropped in favor of mineral-based oils around 1925-1935. At the time, these oils did not contain any additives and compared to today’s engines, oil consumption was extremely high, with engines requiring regular top-ups.

Additives, such as ashless dispersants, help to reduce engine oil consumption. But before delving into the importance of ashless dispersants in aviation engine oils, it is important to understand what an ashless dispersant is. Ashless dispersants help prevent metallic deposits from forming in engines, which can cause pre-ignition and can result in catastrophic damage to the engine.3 An ashless dispersant works by dispersing accumulated ash out of the engine’s components to prevent buildup and excessive wear.

The Aircraft Owners and Pilots Association (AOPA) states that “ashless dispersant oils have an additive in them to aid in scavenging debris and carrying it to the filter or screen.”4 AOPA further states that “This is a very important quality, given the relatively high wear of aircraft engines and the amount of combustion acids and other contaminants that get past the cylinder rings and valves.” In effect, an ashless dispersant functions by surrounding unwanted debris to prevent it from settling and causing wear and other damage such as pre-ignition.5

Aircraft piston engines deviate from the design and construction of modern automobile engines on many counts, most notably in their powerbands. An automotive engine typically has a redline of around 6,000-7,000 revolutions per minute (rpm) and rarely operates at peak power for more than a few seconds at a time, whereas an aircraft engine typically outputs peak power at around 2,700 rpm and operates at this level for the majority of its operation,6 with the higher end being those of World War II (WWII) aircraft, which peaked at 3,200 rpm.

Another difference is in the overall objectives in engineering these types of engines. Currently, the automotive industry is focused on improving fuel efficiency by downsizing, and providing convenience for both vehicle drivers and passengers. In contrast, airplane engines are focused on reliability and simplicity. A prime example of this is the Lockheed Constellation, which is a World War II aircraft that was named the “safest 3-engine plane,” despite its 4-engine design, because overseas flights often resulted in one engine dying along the way.

During World War II, water-cooled engines were predominantly V12 designs, while air-cooled engines were star-shaped single or twin-star designs with seven to nine cylinders per star. Power density increased rapidly during World War II; aircraft engines were 20-50 liters in displacement and were often turbocharged, first invented in Germany and later supercharged by the Allies. The octane rating of the fuel used was usually 90 octane or less, rising to 100 octane and even as high as 150 octane during the war, in stark contrast to today's 100 octane, which is free of lead and sulfur.

These engines developed about 50 hp/liter, and could be supercharged by 50% with water-methanol injection for up to 90 seconds. Today, mass-produced gasoline passenger car engines have power of 100-150 hp/liter, a significant improvement in engine technology over the past century. One of the issues that plagued both sides during World War II was engine reliability, even when not in contact with the enemy. Due to insufficient and lack of maintenance, limited knowledge of additives and the resulting premature ignition, soot and deposits formed, causing major problems. This was the birth of synthetic engine oils and functional additives. The base oil used by the Luftwaffe was an ashless diester blend with polyethylene oil 7, mixed with the extreme pressure/antiwear additive "Mesulfol II" (a sulfur carrier). In 1944, the USAF's P-38, P-47, P-51 and B-25⁸ fighters began using Bridgestone (Union Carbide) ashless polypropylene glycol. Both oils were retired after World War II, but polyalkylene glycols (PAGs) still have some self-cleaning and dispersant properties.

Comparing a 1960s car engine to a modern engine shows some obvious changes and progress, while comparing two aircraft engines shows that the two engines look very similar. Figures 2 and 3 show a comparison of two engines from 1967 and 2015.

Comparing automotive and aircraft engines is crucial to understanding why ashless dispersants are still common in aviation engine oils, but rarely mentioned when discussing automotive engine oils. A Google search for "ashless dispersant" will turn up almost all results related to aircraft engines and aircraft engine oils. The advanced technology of new cars is designed to keep the engine in pristine condition for as long as possible to make the most of the fuel in the tank, not to mention that electric cars don't need engine oil. However, older aircraft piston engine designs are more like 1960s automotive engines, which rely on some deposits remaining in the engine and are not designed to run in "like new" conditions throughout their service life.

As a result, automotive manufacturers tend to recommend fully synthetic, medium SAP (sulfated ash <0.80 wt.-%) or low SAP (sulfated ash <0.50 wt.-%) oils with complex additive packages, while aircraft manufacturers generally endorse two more basic oils: straight mineral oil and ashless dispersant mineral oil. SAP stands for sulfur, ash and phosphorus. Straight mineral oils (API Groups I-III) are essentially oils produced from a refinery and are often recommended for the break-in period of new aircraft piston engines.

According to Ben Visser, retired lubrication specialist at AeroShell, “Previously, cylinder lubrication required a traditional hard chrome treatment to meet specifications, and the wear particles acted as an abrasive.”13 After the break-in period, recommendations are adjusted to prevent additional, unwanted deposits. Most aircraft manufacturers recommend using ashless dispersed oils instead of straight mineral oils after the break-in period to remove excess metal particles and contaminants.

Despite the durability of these ashless oils in aircraft piston engines, there is one potential challenge to the long-term durability of ashless dispersed oils: electric aircraft. In 2014, Klaus Ohlmann set seven world records in his two-seater e-Genius. These included a speed record of 142.7 mph (229.7 km/h) and a total flight distance of 313 miles (504 km). These results are not groundbreaking in the context of all aircraft, but knowing that the e-Genius accomplishes these feats using only an electric motor and a battery as its power source is a remarkable achievement in itself. 14, 15 Even more impressive is that the e-Genius consumes only one-fifth of the energy required to travel the same distance in a fuel-powered two-seater aircraft. 15 These results are promising for the future of electric aircraft, but what do they mean for aircraft fuel?

The “e-Genius” from the University of Stuttgart in Germany looks like a futuristic glider, but there are other more complex electric aircraft concepts. From all-electric aircraft to hybrid aircraft, electrification as a vision of the future is “in vogue” in aviation. Eviation has unveiled its nine-passenger commuter aircraft “Alice” with an estimated range of 600 miles. Airbus has unveiled its e-fan X, which can carry more passengers, with one of the engines replaced by a 2-megawatt electric motor. 17 NASA’s experimental all-electric X-57 aircraft features large electric wingtip engines for cruising, and 12 smaller electric motors with folding propellers for takeoff.

Vertical take-off and landing (VTOL) aircraft are another category of electric aircraft. They focus on regional air traffic and connecting city centers as “urban air taxis” because they only need a landing pad. Examples include: CityAirbus, Daimler Velocopter, Boeing NEXT, and Lilium jet.

It’s clear that the world is moving toward electric technology. The technology has already taken hold in the automotive industry, with sales of the Chevrolet Volt, Nissan Leaf, Toyota Prius Prime, and Tesla’s lineup growing year after year. 19 Aircraft like the e-Genius are also demonstrating the potential for this technology to be shared with the aviation industry, but that doesn’t mean the advent of electric aircraft spells the death of aviation engine lubricants.

According to General Aviation News, the average age of a general aviation* aircraft is 50 years, with an average year of manufacture in 1970. 20 By comparison, the average consumer car is just 12 years old, with an average year of manufacture of 2008. 21 In theory, this means that a new feature or regulation would not be mandatory until 2032. This makes it harder to change aviation technology, for better or worse. In the case of aviation engine oils, this has hampered the adoption of technologies such as full synthetic oils with complex additive packages in aircraft, but it has also helped ashless dispersants survive the current global interest in alternative fuels and stricter emissions standards.

Clearly, there is competition between aviation and electrification. The goal is to achieve CO2-neutral transport, and aviation is ahead of the automotive industry in this regard. ASTM D7566, the key specification for traditional jet fuel, currently has seven annexes that define different pathways for sustainable aviation fuel (SAF), allowing up to 50% SAF to be produced from different sources such as biomass resources and processes. This can be a blueprint for internal combustion engines. BMW recently announced that it has approved a 100% renewable diesel fuel, known as HVO100. HVO100 is a chemical replica of hydrocarbon diesel. Porsche promotes the development of synthetic fuels or electrofuels, which are produced from CO2 and hydrogen using renewable energy. Another option is to blend the fuel with 33 vol.% hydrogenated waste cooking oil to produce petroleum diesel, as Volkswagen has proposed with the R33 BlueDiesel.

While the mechanical structure of aircraft engines has remained largely unchanged over the past half century, the mechanical structure of automotive engines has changed significantly. Despite this great difference in development history, it is expected that electrical technology will penetrate both industries in the coming years. While this may lead to a decrease in the amount of aircraft engine lubricants used, the continued existence of older aircraft with simple piston engine designs will most likely lead to the continued existence of ashless dispersed aviation engine lubricants. Ashless dispersed lubricants may not see many new developments and improvements in the next few years, but like the aircraft they serve, they are likely to continue to exist for many years to come.