BASIC LUBRICATION DESIGN

TBN and OXIDATION

Engine lubricants are generally used to reduce friction between moving parts within the interior engine. In addition to the lubricating function, motor oil also serves as a coolant, corrosion protector, and method of removing contaminants from the engine filter. In other words, motor oil holds the same importance to an engine that blood holds for humans. Loss of any essential function of the motor oil will lead to serious engine damage if not treated. Through the oxidation of motor oil, its essential functions are destroyed. This degradation usually begins cause severe engine damage.

carmadman

As lubricants degrade, their physical properties (e.g. viscosity) change, leading to increased friction and wear. This degradation is primarily due to base oil oxidation. Oxidation is due to free radical attacks against the Base oil's chemical composition. Base oil is the petroleum component of the lubricant. Generally, the base oil comprises eighty percent of the lubricant, with the remainder being additives.
Virgin Oil from Bottle Oxidized Oil
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To fight oxidation in oil we use antioxidants. This fights and terminates free-radical reactions that attack the Carbon hyd bond and destroys the base oil thus creating higher levels of oxidation and putting more demand on the detergents.

Detergents are used to clean up the by product of oxidized oil which occurs when antioxidants can't neutralize the acids effectively by creating a chemical reaction with sludge, and varnish precursors so to neutralize them and keep them soluble.

Total Base Number does not measure the accumulation of oxidation products or antioxidants, rather, it measures the depletion of a detergents present in an engine oil for the purposes of neutralizing acidic blow-by gases which occurs due to low levels of antioxidants with in the oil. As the detergent is consumed in its role of neutralizing sludge and varnish, the base number decreases from its original new oil value. Monitoring this consumption allows one to proactively replenish the oil through change out before the protection afforded by that additive is lost.

This is one reason why higher levels of TBN's can mislead you into thinking it is better when in fact all it is stating is that it has higher levels of detergents to keep the engine clean but the base oil can oxidize(or breakdown) faster than one with higher levels of antioxidants which prevents the acids by neutralizing the attacking acids as oppose to cleaning up the by products of the oxidized oil.

More on Additives

Very little unadditized mineral oil is sold as a lubricant. Almost all commercial lubricants contain additives to enhance their performance in amounts ranging from less than 1% to 25% or more. By far the largest market for such additives is in the transportation field, including additives for engines and drivetrains in cars, trucks, buses, locomotives and ships. The function of additives can be summarized as:

* Protect metal surfaces (rings, bearings, gears, etc.)
* Extend the range of lubricant applicability
* Extend lubricant life

HYDRODYNAMIC LUBRICATION

The design of oil is to produce a film of oil between two mating surfaces which gives you the best protection against wear. As the image below shows, oil flows, and creates a hydraulic pressure (elasto-hydrodynamic lubrication,EHL) between the two surfaces. Now under perfect conditions this type of lubrication will not allow wear. But in reality, this is not always the case.This takes us to the next state of lubrication.

hydrodynamic lubrication
(magnified surfaces show mating sides are not smooth)
MIXED FILM LUBRICATION
This is where lubrication is marginal. Under load conditions oil is squeezed under pressure. For example, during accelleration of an engine, you step on the gas and the engine dumps fuel, in turn the force is increased against the rod bearings, pushing (or squeezing) on the hydrodynamic oil creating a marginal lubrication condition. This is under normal use. But what happens to oil when it is under extreme pressure created by abuse or just a heavy foot? Follow me to the next state of lubrication.
mixed_film_lubrication
(magnified surfaces show mating sides are not smooth)



BOUNDARY LUBRICATION

This is where lubrication is dependant on antiwear additives. What happens here, is lubrication can be put under so much pressure, and is momentarily squeezed out to such a point that if oil didn't have any antiwear additives, you would be metal to metal. This is the last line of defense for lubrication to protect your equipment. A common place where you see a lot of high levels of barrier lubricant is in gear lubes. Ever wonder what that rotten smell was? Yep, high levels of zinc, and phosphorus. These are the two most used antiwear wear additives used in oils today.

boundary_lubrication
(magnified surfaces show mating sides are not smooth)

A lot of aftermarket additives use zinc and phosphorus for extra protection. The problem is, when you overload an oil with this type of additive, your oxidation levels tend to increase, causing an attack on the base oil, which in turn can cause an increase of viscosity, (thicken the oil) .This is why it is important not to play home chemist and blend in aftermarket additives that are not designed to be in the oil to start with.

So, as you can see, viscosity of the oil isn't the only important factor. Like building a house, you want a good foundation or base. Then you would use a quality product to build with. In this case, a good base oil is a start, then with good additives you achieve a good lubricant. Is zinc and phosphorus the only barrier additives available? No, there are more. Follow me to a barrier lubricant that has been around for a long time and has proven out for many years...