Tagged: lubrication

Is Oil analysis still relevant today?

With the many advancements in Artificial Intelligence, Machine Learning and the advent of countless different sensors on the market, the question arises, “Is Oil Analysis still relevant today?”. Granted that these advancements have significantly transformed the industry, we need to recognize that they are here to help evolve what we already do and not necessary replace it.

These advancements build upon the foundations of the techniques of oil analysis. With artificial intelligence and machine learning, we can train models to interpret oil analysis data and trigger alerts accordingly but there should always be a human present to overview these. In the real world, not every situation has occurred or been recorded yet hence the models do not have that particular data to learn from nor can they make decisions about it since it simply doesn’t exist in their “brain”.

Humans can “think outside the box” and formulate patterns or trends which may not be triggered by the models simply because these models have not been taught these patterns. Hence it is important to always have a human in the loop and not rely solely on these models especially when million-dollar decisions can be negatively initiated with the wrong interpretations.

Lately, sensors have gained more traction and a wider adoption as they can be integrated into warning systems to alert users to potential deviation from known characteristics of the oil. However, as noted above, sensors rely on data sets to compare the information and on some form of capacitance which must be converted into a signal before it can be interpreted.

With lab equipment performing the actual tests, there is a higher rate of accuracy plus the added advantage of having humans review the results for discrepancies before sending off the report. While sensors can be the first warning system for some users, lab equipment should be utilized for those more precise tests which require a higher level of accuracy.

In essence, oil analysis remains very relevant today. However, it has significantly evolved over the last few decades. Today, oil analysis can achieve a higher efficiency level with the integration of the advancements in technology (AI, machine learning and sensors) and other available monitoring technologies. Together, these should all be used to create a greater impact on improving the reliability of the machines.

Find the full article here on Engineering Maintenance Solutions Magazine.

Oil Properties / Used Oil Analysis

Oil analysis vs Other technologies

Just as oil analysis is similar to blood testing, we can think of our bodies as a critical machine with various components which need to be monitored. If we get a fractured bone, a blood test will not help us to assess if the bone is broken or can be repaired. In this case, we may need an x-ray. Similarly, with machines, there are various types of tests to determine different aspects to be monitored.

Typically, oil analysis can provide the operator with insight into whether there has been any internal damage to the equipment in the form of wear particles which can be quantified. As with most condition monitoring methods, being able to trend the patterns over time helps the operators to identify if wear is occurring at an increased rate or whether the oil is degrading.

On the other hand, other technologies such as vibration analysis or ultrasound analysis or even thermography are not able to detect the presence of molecules. These other types of analyses focus on alignment, or other mechanical issues as they occur and can trend them over time. However, oil analysis can accurately detect the presence or absence of contaminants or additive packages which could affect the health of the oil and by extension that of the machine.

Oil analysis should not be used as the only technology in your condition monitoring artillery. Other technologies can be used alongside oil analysis to provide the user with a more comprehensive overview of the health of the asset. For instance, if the oil analysis discovered high wear, the next step would be to identify where the wear was coming from. Perhaps in this case, one of the other technologies could identify a misalignment or other mechanical issue which could be the source of this wear. Thus, these technologies should be used to work together to achieve better reliability for their asset owners.

Find the full article here on Engineering Maintenance Solutions Magazine.

Oil Properties / Used Oil Analysis

Why oil analysis?

The P-F curve is one that is used throughout reliability to demonstrate the point at which a component is expected to have a functional failure. There are many variations of the PF curve, and different monitoring technologies can be placed in specific orders accordingly. However, it remains dominant that oil analysis is among the top three techniques used for early detection of failure.

Oil analysis can be used to detect the presence of contaminants, metals and other molecules at a microscopic level and quantify these appropriately. Most OEMs (Original Equipment Manufacturers) publish their acceptable standards for various tests (usually standardized tests by some accredited body such as ASTM) and have these available to laboratories around the world. When an oil analysis test is performed (as per the stipulated standards), the lab will compare the actual values to the expected values (from the OEM) and then provide some guidance to the user on possible steps forward.

Every lab will have a specific format for reporting the results of your oil analysis (similar to the labs for reporting on blood samples). Typically, the actual value is shown and then there may be an expected range for the various characteristics or just an indication of whether the actual value falls outside of the range (on the higher or lower end of the scale).

Bureau Veritas, 2017, gives an example of a report and all of the variables involved here:

BV_Understanding-An-Oil-Analysis-Report_FINAL_11_8_2017

While this is their reporting standard, other labs will have a different format, but the tests will all conform to the same internationally recognized standard. As such, if oil is tested in the United States (as per a particular standard) and then tested in Italy (as per the same standard) then there can be some comparisons of these results. However, one must also be aware of the types of instruments being used and their calibration as this can account for slight differences in test results. As such, oil analysis provides a global standard for which equipment performance can be compared across regions.

Find the full article here on Engineering Maintenance Solutions Magazine.

Oil Properties / Used Oil Analysis

What is oil analysis?

For those not familiar with oil analysis, it can be likened to performing blood tests for the human body. Oil in our machines is often compared to the blood in our bodies. Blood circulates throughout the body taking important blood cells with food and oxygen in it to the various organs, similarly oils follow this behaviour. However, oils transport additives which provide varying functions including reducing wear or friction or even preventing corrosion or oxidation to name a few.

When performing a blood test, we can test for a few things; the overall condition of the organs or we can test for specific things such as the presence of bad cholesterol. With oils, we do a very similar practice where we can test for the overall health of the machine or pinpoint exact components and look for distinct changes which are reflected in the characteristics of the oil.

Basically, oil analysis can help you to determine the condition of your oil (if it is degrading or if the additives have depleted such that it no longer protects the equipment) and the health of your asset as the oil can reflect if there is wear occurring in the components. As such, it can provide very useful information to help operators and maintenance personnel to plan effectively for any type of maintenance to be done on the components.

Find the full article here on Engineering Maintenance Solutions Magazine.

Oil Properties

What are some innovations and future trends of Viscosity Index Improvers?

Innovations in Viscosity Index Improvers

As per Mortier, Fox, & Orszulik (2010), the three most important commercial VII families represent critical commercial techniques for manufacturing high molecular weight polymers. These are polymethacrylates produced by free radical chemistry, olefin copolymers produced by Ziegler chemistry, and hydrogenated styrene-diene or copolymers produced by anionic polymerization. While they are critical, these formulations will not be discussed in detail in this article, but we will take a look at some of the innovations within this space.

PARATONE®a, a family of viscosity index improvers currently belonging to Chevron Oronite, boasts of having developed the first Olefin Copolymer VII (Mid Continental Chemical Company Inc, 2024). However, upon further investigation, it must be noted that Exxon Chemicals was the original developer behind this product. Back in 1998, Oronite Additives, a division of Chevron Chemical Co. LLC, acquired the assets of Exxon Chemical’s Paratone crankcase olefin copolymer (OCP) Viscosity Index Improver Business (Chevron Chemical Co. LLC, 1988).

This particular Viscosity Index Improver has seen developments since the 1970s and offers solid and liquid VIIs for companies to include in their formulations (Chevron Oronite, 2024). It also allows improved formulating flexibility for developers, which can significantly reduce the costs involved or specialized base stocks depending on the product to be made. This is just one company that specializes in producing VIIs for the wider global market.

There are many other companies that have innovated in the Viscosity Index Improver space, but most of this work is patented as it involves heavy-balanced formulations. Other companies have also innovated on the production side of the VIIs by engineering equipment that can help produce a higher-quality VII.

Future Trends

(Future Market Insights, 2024) estimates the Viscosity Index Improver market will be USD 4.06B in 2024 and will increase to USD 5.39B by 2034. Additionally, in 2024, vehicle lubricants account for around 51.6% of the VII market. This is not just limited to the multigrade oils but includes transmission fluids, greases, and other oils. On the other hand, with the move towards more sustainable oils, Ethylene propylene Copolymer (OCP) is projected at a 30.4% industry share in 2024. Given the move towards more sustainable products, this is expected to increase.

If we take a global view of the compound annual growth rate (CAGR) per country to 2034, we can find some interesting facts. The United States shows a CAGR of 1.6%, with a heavy allocation towards more vehicle engine oil use and the manufacturing sector for pharmaceuticals and chemicals. On the other hand, Spain is projected to see a CAGR of 2.2% with auto manufacturers and power generation equipment (hydraulic oils, turbine oils, and greases).

Venturing to China, they have a CAGR of 3.2% due to the increased number of vehicles and significant industrialization. Their involvement in complex machinery will also drive this growth. The United Kingdom is positioned to see a CAGR of 1.1% resulting from its rise in high-performance engines and heavy industrialization. On the other hand, India should experience a CAGR of 4.3% with its high demand for industrial production, commerce, and automobiles.

Figure 2: CAGR% per country to 2034

With these positive CAGRs, it is conclusive that there will be a lot of growth within the VII industry. (Future Market Insights, 2024) also list some of the recent developments in the VII Market, which include:
In July 2023, Chevron Phillips Chemical announced a capacity expansion of its VII productions to meet the increasing demand for VIIs in the automotive and industrial sectors.
In April 2023, Lubrizol introduced a new line of viscosity index improvers (VIIs) for automotive lubricants, claiming to offer enhanced performance, including improved oxidation and thermal stability.
In March 2023, ABB completed the Marunda 2.0 oil blending plant extension project, doubling production capacity within three years despite challenges during the pandemic.
In October 2022, LCY Chemical Corp., a Taiwanese material science company, showcased its thermoplastic elastomer portfolio at K 2022. It highlighted its innovative approach to material science for a sustainable future, backed by a global distribution network.
In August 2022, Evonik’s Oil Additives division in CIS countries partnered with ADCO to enhance the energy productivity and effectiveness of industrial lubricants for construction, agriculture, mining, and manufacturing equipment.

From this, the future of Viscosity Index Improvers can only be enhanced by several of the major key players expanding their operations and innovating their creations to adapt to ever-evolving standards/guidelines set by OEMs and governments. As new regulations emerge regarding improved efficiency, increased oxidation stability, and thermal stability for lubricants, VII developers will be challenged to innovate new solutions for the lubricants to conform.

References

Chevron Chemical Co. LLC. (1988, October 08). Oronite Additives Acquires Exxon’s Paratone Viscosity Improver. Retrieved from Pharmaceutical Online: https://www.pharmaceuticalonline.com/doc/oronite-additives-acquires-exxons-paratone-vi-0001

Chevron Oronite. (2024, June 29). PARATONE® viscosity modifiers. Retrieved from Oronite: https://www.oronite.com/products-technology/paratone-products.html

Future Market Insights. (2024, April 15). Viscosity Index Improver Market Forecast by Vehicle and Industrial Lubricant for 2024 to 2034. Retrieved from Future Market Insights: https://www.futuremarketinsights.com/reports/viscosity-index-improvers-market

Gresham, R. M., & Totten, G. E. (2006). Lubrication and Maintenance of Industrial Machinery – Best Practices and Reliability. Boca Raton: CRC Press.

Mid Continental Chemical Company Inc. (2024, June 29). Viscosity Modifiers / Viscosity Improvers. Retrieved from Mid-Continental Chemical Company: https://www.mcchemical.com/lubricant-additives/viscosity-index-improvers

Mortier, R. M., Fox, M. F., & Orszulik, S. T. (2010). Chemistry and Technology of Lubricants – Third Edition. Dordrecht: Springer.

Want to read the entire article? Find it here in Precision Lubrication Magazine!

Oil Properties

What impact do Viscosity Index Improvers have on Efficiency, Wear, and Degradation?

If we filled a swimming pool with honey during the winter when no heating was available, the honey would crystallize and become more viscous. Hence, if anyone tried to walk through the pool, moving would be difficult and require more energy. However, if heating was available to the pool, then the honey would be more fluid, and someone could walk a bit more freely (although still sticky at the end of the day!). As such, they would not have to exert as much energy.

The same applies to lubricants and their viscosities. If the lubricant is too viscous (thick honey in the winter), then more energy is required for the components while they are moving. For systems with varying temperatures, finding a lubricant that can maintain the desired viscosity for those changes is challenging.

However, with the invention of Viscosity index improvers, oils can now maintain a desired viscosity at variable temperatures. This significantly affects the energy the system requires and can reduce the energy needed, making some systems more efficient.

As such, the system’s overall efficiency is impacted, and less energy is required to overcome the internal frictional forces of the lubricant (as its viscosity remains within the required range). Passenger car engine oils saw this change with the integration of VIIs when multigrade oils were invented. They no longer needed one oil for summer and another oil for winter. This significantly saved many owners from draining and replacing their oils seasonally or finding their oil frozen in the winter!

Viscosity index improvers, therefore, enhance the overall efficiency of these systems by maintaining the lubricant’s viscosity throughout the changing temperatures. Subsequently, there is no need for additional heaters in the lube oil system, which would also require additional energy. This is another area where cost and energy savings can also be achieved.

Maintaining a particular viscosity at variable temperatures allows the lubricant to form a full film (also known as hydrodynamic or elastohydrodynamic lubrication) between the two surfaces, thus offering them protection from wear.

If the viscosity became reduced (due to an increase in temperature without the VII), then the lubricant would not form a full film or experience boundary or mixed lubrication. In this case, there is the potential for increased wear, which will negatively impact the components in the system. As such, using VIIs can also reduce the potential occurrence of wear or aid in reducing wear.

As per (Gresham & Totten, 2006), this does not mean that the viscosity never changes. When the viscosity of a lubricant changes, its viscosity index will change accordingly. If the viscosity index decreases, this can likely be because of the breakage of the polymeric Viscosity Index Improver polymer molecules to produce smaller chains, which essentially reduce its originally intended effect. If there is a reduction in the molecular weight of the VII, then the lubricant will see a reduced viscosity at both 40 & 100°C. This also reduces the temperature related viscosity effect.

Viscosity Index Improvers significantly improve a system’s overall efficiency and can help reduce wear. However, these additives can degrade over time with high temperatures and shear stress.

Want to read the entire article? Find it here in Precision Lubrication Magazine!

Oil Properties

What is the role of Viscosity Index Improvers in Lubricants?

Viscosity Index Improvers began their commercial debut around the 1950s to accommodate the new developments in automotive oils, which were then adapting multigrade viscosities. However, they were used even before (back in the 1930s) when workers in crude distillation realized that small amounts of rubber improved the VI of the oil but also increased sludge formation.

Today, VIIs are still primarily used as engine lubricants. They can also be found in automatic transmission fluids, multipurpose tractor transmission fluids, power steering fluids, shock absorber fluids, hydraulic fluids, manual transmission fluids, rear axle lubricants, industrial gear oils, turbine engine oils, and aircraft piston engine oils. (Mortier, Fox, & Orszulik, 2010)

Essentially, VIIs try to maintain the oil’s viscosity at varying temperatures. They try to ensure that the oil does not experience a loss of viscosity, which can occur due to high temperature or shear. VIIs can be considered polymers, which are tightly wound coils. When temperature or shear is applied to these coils, they unravel (lose their viscosity). Depending on the amount of shear, they may never recover their original shape (or viscosity).

As seen in Figure 1 below, Mortier, Fox, & Orszulik (2010) describe the change in the shape of the VIIs as a result of high temperature or shear. They can coil and uncoil depending on the shear stress, but if the bonds are broken, they will not reform their original coil and lose their intended viscosity.

Figure 1: Mechanical Polymer Degradation (excerpted from (Mortier, Fox, & Orszulik, 2010)

Interestingly enough, it must be noted that some VIIs provide lubricants with additional functions of Pour point depression and dispersancy. This is highly dependent on their composition.

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Oil Properties

What are Viscosity Index Improvers?

Viscosity Index Improvers (VIIs) are additives that help maintain the viscosity of lubricating oils across a wide temperature range, ensuring consistent performance.

This article will explore the nature of viscosity index improvers and their role in industrial and automotive lubricants. We will also look at their impact on lubricant efficiency, innovations involving this type of additive, and future trends.

Before discussing the nature of viscosity index improvers, we need to understand the role of viscosity. Essentially, this is one of the most critical functions of a lubricant, as it directly affects its flow rate and ability to keep the two interacting surfaces apart.

By nature, all base oils have an assigned viscosity based on their blend. However, other properties are required when we’re creating finished industrial or automotive lubricants. For instance, we may need the oil to withstand higher temperatures while still maintaining a particular viscosity, which not only provides wear protection for the equipment but also flows at a rate that does not incur frictional losses. Those are a lot of functions!

Typically, as temperature increases, viscosity decreases, and as the temperature decreases, the viscosity increases. One example is the state of water: when heated, it can turn into a gas (lower viscosity), or when frozen, it can transform into ice (higher viscosity). However, depending on the type of material, there will be varying rates of viscosity change with temperature. The viscosity/temperature relationship is called the viscosity index (VI).

As per Mortier, Fox, & Orszulik (2010), the kinematic viscosity of oil is measured at 40°C and then at 100°C. The viscosity change is then compared with an empirical reference scale initially based on two sets of crude oils: a Pennsylvania crude arbitrarily assigned a VI of 100 and a Texas Gulf crude assigned a VI of 0.

The higher the VI, the less effect that temperature has on the oil, which means that the oil can maintain a particular viscosity for a longer time at a more extensive temperature range. This is ideal for lubricants in environments experiencing temperature changes. However, not all oils have a high viscosity index. Typically, paraffinic oils can have a very high viscosity index. On the other hand, naphthenic oils have a low or medium viscosity index. The table below gives an overview of the viscosity index for various oils.

Table 1: Viscosity index of API Groups I-III

When trying to manage or alter the viscosity index of the oils above, the use of Viscosity Index Improvers (VII) can help by adding that property to an oil to allow it to have other beneficial properties. As per (Mortier, Fox, & Orszulik, 2010), viscosity index improvers consist of five main classes of polymers:

Polymethylmethacrylates (PMAs).
Olefin copolymers (OCPs).
Hydrogenated poly (styrene-co-butadiene or isoprene) (HSD/SIP/HRIs).
Esterified polystyrene-co-maleic anhydride (SPEs)
A combination of PMA/OCP systems.

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Oil Properties

Understanding the oil analysis results of Diesel Engine Oil

Having the information above is great to understand how your diesel engine oil degrades, but how will you know that it is degrading? One of the most reputable ways is to submit your oil for testing in the lab. Depending on the type of diesel engine (on-highway, marine or off-highway), different tests will be involved. However, here are the basic ones that you should be familiar with.

When determining the health of your diesel engine oil, the first thing to check is the oil’s viscosity, total base number (TBN), whether all the additives are at the correct levels, if there are any wear metals or contaminants present and finally the presence of water or fuel dilution as shown in Figure 3.

Figure 3: Basic oil analysis tests for your diesel engine

Viscosity (American Society for Testing and Materials D445) – The viscosity levels should ideally fall within ±5% of the original value. If they exceed ±10% of the original value, then the levels will fall out of the classification for that grade of oil.

For instance, Mobil Delvac 15w40’s kinematic viscosity, at 100°C, is 15.6 millimeters squared per second (mm²/s), according to its technical data sheet. If this value drops below 14.04 mm²/s or above 17.16 mm²/s then it can no longer be classed as a 15w40 oil and will not be able to properly lubricate the engine. These values vary depending on the manufacturer, application of the oil and the lab being used. These are a guideline in this example.

TBN– This is the amount of alkalinity remaining in the oil. The oil’s alkalinity helps neutralize the acids formed in a diesel engine. This value is always depleting as acids are continuously forming in an engine. However, if the TBN value drops below 40% to 50%, then there isn’t much reserve left to continue to protect the oil. This is the threshold limit, which can vary depending on the application, but this is a good guide to follow.

Additives – All finished lubricants have additive packages. These will vary depending on the oil producer. However, a few additives should be on your radar when trending their depletion in diesel engine oils. These include zinc, phosphorus, magnesium and calcium. These additives typically form parts of the dispersant, corrosion and antiwear additives that protect the oil. Ideally trending the decline of these may be helpful but your lab would have reference values (based on the type of oil) and can advise on concerning levels.

Wear metals – During the engine's lifetime, components will wear. Depending on the engine’s manufacturer, the warning limits will also vary (this also differs depending on the application). Iron, aluminum, chromium, copper, lead, molybdenum and tin are some metals to trend. If other special metals are in your engine, then you can ask your lab to include them in the oil analysis report. Typically, if there is an upward trend, this indicates wear/damage of specific components.

Operators can perform a simple test to determine if metal filings are in their oil (indicating some form of wear). They can place the oil in a shallow container and then place a magnet below the container or place the magnet in a sealed plastic bag and immerse it into the container. When the magnet is removed, if there are metal filings on the magnet, then this indicates the presence of wear metals, and the mechanic should begin investigating for damaged components.

Contaminants– These include any material which is foreign to the lubricant. Typically, labs test for the presence of sodium and silicon. Depending on the application’s environment, these values can increase indicating that they are entering the system somehow. Usually, this can occur during lubricant top-ups or improper storage and handling practices.

Presence of water – This is never a good sign because water can affect the lubricant by changing its overall viscosity, bleaching out some of the additives and even acting as a catalyst. Many labs perform a crackle test (where the oil is heated and if it produces a “pop” sound, then that confirms water in the lubricant. In certain instances, it is obvious that there is water present because it settles out in the sump/container. Labs can also perform a test to quantify the volume of water present. Typically, 2,000 ppm to 5,000 ppm is too much for most applications but this varies depending on the manufacturer.

Operators can perform their version of the crackle test by placing some of the oil in a metal spoon and heating it with a flame. If it produces a pop, then they can confirm that the oil has too much water in it before sending it off to the lab. Note: This should not be done in a highly flammable environment!

Fuel dilution – This occurs in most diesel engines due to the nature of the engine. However, limits need to be adhered to because too much fuel in the oil can lead to drastic changes in its viscosity. Usually, this value should not exceed 6%, but this can vary depending on the application and the manufacturer.

One way that operators can find out if there is fuel in their oil is to place a small drop of the oil on a coffee filter and leave it to “dry” for some time. The oil will spread out in concentric rings and if there is fuel present, there will be a rainbow ring. This means that the mechanics need to figure out if there is an issue with any of the injectors or seals in the diesel engine.

Ideally, the main idea with oil analysis is to develop a trend for your equipment and understand how the values align over time. This can help operators spot if an inaccurate sample was taken (possibly after a top-up, directly after an oil change or even from the bottom of the sump). An analysis also assists in planning the maintenance of components. For instance, if the value of iron in the oil analysis report keeps increasing then there is a strong possibility that some iron component is wearing. This can give the mechanic the time they need to investigate the engine and replace the component before it causes unscheduled downtime.

Protect One of Your Greatest Assets

Your diesel engine oil is one of the greatest assets in your fleet. You should be able to use an oil that aligns with your application while slowing its degradation rate with good practices and managing its health. Diesel engine oils form a critical part of your operation and deserve attention.

References

American Petroleum Institute. (November 18, 2016). New API Certified CK-4 and FA-4 Diesel Engine Oils are Available Beginning December 1. Retrieved from API: https://www.api.org/news-policy-and-issues/news/2016/11/18/new-api-certified-diesel-engine-oils-are

American Petroleum Institute. (February 19, 2024). API's Motor Oil Guide. Retrieved from API: https://www.api.org/-/media/files/certification/engine-oil-diesel/publications/motor%20oil%20guide%201020.pdf

The International Council on Combustion Engines. (2004). Guidelines for diesel engines lubrication - Oil Degradation | Number 22. CIMAC.

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equip-today - evolution-diesel-June-horz

Oil Properties

Why Does My Diesel Engine Oil Degrade?

All oils degrade over time. They can be considered consumable items as they must be replaced over time. Diesel engine oils are no different except that they may be susceptible to certain mechanisms that turbine oils are not. The diesel engine is often placed under a lot of pressure to deliver power while keeping cool and managing emissions.

The critical areas for lubricant performance in a diesel engine usually include:

Viscosity control
Alkalinity retention, base number (BN)
Engine cleanliness control
Insoluble control
Wear protection
Oxidation stability
Nitration

Typically, these factors are monitored in these types of oils to ensure that they remain in a healthy condition.

Several factors affect oil degradation in a diesel engine. According to The International Council on Combustion Engines (The International Council on Combustion Engines, 2004), these include specific lube oil consumption; specific lube oil capacity; system oil circulation speed; NOx content in the crankcase atmosphere; and influence on the lubricant, fuel contamination in trunk piston engines, deposition tendency on the cylinder liner wall, metals in lubricant systems, and oil top-up intervals. These can further be divided into systemic conditions (which cannot be easily altered) and environmental conditions (because of processes occurring within or to the system) as shown in Figure 2.

Figure 2: Systemic & Environmental Conditions which affect degradation of diesel engine oil

Systemic Conditions

While lubricant degradation can be caused by environmental strains being placed on the lubricant, there are times when the operating design of the system also encourages degradation. Three such cases for diesel engine oils are specific lube oil consumption, specific lube oil capacity and system oil circulation speed.

Specific lube oil consumption (SLOC, g/kWh) is defined as the oil consumption in grams per hour per unit of output in kilowatts (kW) of the engine (The International Council on Combustion Engines, 2004). Over the years, there has been a reduction in the SLOC for engines with special rings inset into the upper part of the cylinder liner. These reduce the rubbing of the crown land against the cylinder liner surface.

With reduced oil consumption, oil top-ups, which would have introduced fresh oil into the system, are consequently reduced. This fresh oil would have increased the presence of additives and helped in maintaining the required viscosity of the current oil. However, since the SLOC is reduced, the oil does not get a “boost” during its lifespan and will continue to degrade at its current rate. Hence, a lower SLOC may encourage the degradation of diesel engine oil.

Specific lube oil capacity, also known as the sump size, which is the nominal quantity in kilograms (kg) of lubricant circulated in the engine per unit of output in kW. According to The International Council on Combustion Engines, the specific oil capacity does not directly affect the equilibrium level of degradation. However, it can influence the rate at which deterioration occurs as smaller sump sizes can increase the rate at which degradation achieves an equilibrium level. Typically for dry sump designs, the specific oil capacity is around 0.5 kg/kW to 1.5 kg/kW. These values are closer to 0.1 kg/kW to 1.0 kg/kW for wet sumps.

System oil circulation speed refers to the time taken for one circulation of the total bulk oil. In diesel engines, lubricants are usually subjected to blow-by gas (including soot and NOx) during their time in the crankcase. If the lubricant spends a longer time in the crankcase, it can become degraded at a faster rate. Typically, the time required for one circulation of bulk oil averages between 1.5 minutes to 6 minutes. However, we have seen the trend toward smaller sump sizes and, by extension, shorter circulation times, which should reduce the degradation rate.

Environmental Conditions

The environmental conditions that lubricants must endure can also influence their degradation. These conditions can either be enforced through the system, its operating conditions or from conditions outside the system. There are a few environmental conditions which must be addressed (The International Council on Combustion Engines, 2004).

NOx content in the crankcase atmosphere and influence on the lubricant has more applicability to gasoline engines compared to diesel engines but they should not be fully ruled out. Diesel engines are more susceptible to sulfur-derived acids (caused by the burning of diesel fuel). However, NOx can be produced by the oxidation of atmospheric nitrogen during combustion, which can affect degradation.

Field studies show a correlation between nitration levels, an increase in viscosity and an increase in acid in the oil. NOx can also behave as a precursor and catalyst that promotes oxidation through the formation of free radicals in the lubricant. On the other hand, there can be direct nitration of the lubricant and its oxidation products to produce soluble nitrates and nitro compounds. These can eventually polymerize to form similar by-products of oxidation. This can lead to increased acidity (lowering the BN) and increased viscosity of the lubricant.

Fuel contamination in trunk piston engines happens quite often in diesel engines. If the fuel injectors are defective or the seals do not effectively seal to keep fuel out, fuel enters the oil. When fuel is in the oil, oil can become degraded quickly, often causing the viscosity to reduce to a value that compromises the ability of the oil to form a protective layer inside the component. The fuel dilution test can quantify the content of fuel in the oil. Depending on the type of engine, the tolerance levels will differ.

Deposition tendency on the cylinder liner wall is usually caused by unburnt fuel or excess oil in this area or the chamber. Typically, the piston rings scrape these deposits back into the oil, leading to an increase in the volume of insolubles. This also increases the viscosity of the oil, and it appears a darker color.

Reducing the SLOC also decreases the deposits on the liner wall because special rings (near the top of the liner) are installed to have controlled clearance of the piston crown. This reduces the crown land deposit which can also minimize bore polish and hot carbon wiping.

In addition, with a reduction in SLOC, the number of oil top ups is also reduced. As such, the replenishment rate of additives (in particular the BN) is not as frequent. Therefore, the degradation of the oil will advance at a slightly faster rate due to the lower SLOC which affects the rate of top up.

Metals in lubricant systems can also act as a catalyst for the degradation of the oil. During the oxidation process, copper is one of the most common catalysts in addition to other wear metals (such as iron) which can increase the rates of oxidation. As such, the presence of these metals increases the degradation rate as well.

Oil top-up intervals must be managed in such a way that it does not disturb the balance of the system. Typically, when the sump level falls below 90% to 95% (depending on the manufacturer), a top-up is needed. When fresh oil enters the system, it replenishes some additives and breathes new life into the oil. However, with this change in temperature of new oil coming into the system (especially in large quantities of about 15%), the deposits held in suspension tend to precipitate.

Additionally, foaming (caused by the increased concentration of some additives) can occur if too much fresh oil is added at once. As such, oil top-up intervals must be managed to avoid further degradation.

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