Motor oil is made up of base oils and additives. Its main purpose is to lubricate the engine and keep it clean. Some of these additives are basic in nature including detergents and anti-corrosive agents.
The basic nature of these additive compounds has a second purpose in addition to their respective primary objective.
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TBN And Its Unit
TBN is a short form of “Total Base Number” which as the name indicates is the total sum of all the base additives available inside the oil.
It is measured as milligram of potassium hydro-oxide per gram denoted as “mg KOH/g”.
How engine oil protects against corrosion?
Following additives inside the oil are responsible for protecting the engine:
- Detergents as bases.
- Antioxidants by preventing the formation of organic acids.
- Corrosion Inhibitors form a protective layer over the engine parts.
What accounts for the base number of Lubricants?
The base is not necessarily added separately inside the oil as it can occupy space and will decrease the volume for the rest of the additives inside of the oil.
That’s why the additives which are added to oil are chosen to be basic in nature.
Well not all of them could possibly be basic but a few of them surely are, for example, the detergents and anti-corrosive agents present in the oil are basic in nature.
TBN in oils for different types of engines
Each type of engine oil has a different quantity of base additives needed due to the difference in the number of acids that are produced in it.
The combustion in diesel engines generally produces a higher number of acids and therefore needs a TBN in the range of 10 to 14 while the gasoline engines having less acid production need TBN from 7 to 10.
How is TBN affected by the oil blend type?
As we all know that synthetic blends of oil have higher additive carrying capacity than semi-synthetic and conventional ones, hence they have more base additives than others. While semi-synthetic have medium quantity and conventional have least.
Why do we need bases in oil?
When combustion occurs within any internally combustible engine it produces different acids as a byproduct.
As we all know that engine parts are metallic in nature and could easily corrode by acids.
Therefore in order to protect the engine, these bases are added into the oil which reacts with the acids to nullify them and maintain the alkaline PH inside.
How are acids produced in the combustion process?
In the engine when fuel is combusted, the oxygen gets burned as a side reaction.
It can not be avoided as the oxygen is abandoned in a closed environment.
This process is called oxidation which leads to the formation of acids.
Types of acids formed during the combustion process
The acids formed during the combustion process can be classified as:
- Sulfuric acids
- Nitrogen acids
- Organic acids
The TAN stands for “Total Acid Number” which represents the total sum of acids within a solution.
In the case of motor oil, the bases react with acids to neutralize them but when the base reserves are low they are unable to counter the acids and hence the TAN grows.
A higher amount of TAN can cause corrosion inside the engine.
Methods to determine the TBN of an oil
There are several methods to find the TBN of any oil:
- Potentiometric titration
- Colorimetric Titration
- Field test kits
- Infrared Spectroscopy
- Photometric determination
- Thermometric determination
- Conductometric determination
TBN relation to the Oil Change Interval
Oil is to be changed if the base reserves in it are low, as they are necessary to perform vital tasks.
With their lower numbers, the oil is unable to properly carry out its duties.
Since detergents and some other vital additives are basic in nature, their lower amount means that the oil must be replaced.
The TBN shows the total base assets and hence is the indicator of how soon an oil must be replaced.
The TBN is higher when the oil has a decent number of detergents as they are all basic in nature.
These detergents fight the sludge whose formation can cause a hindrance in the flow of oil.
If this happens the blockage of smooth oil flow will increase the engine operating temperature.
Hence good TBN is a must requirement for normal engine operation.
Up to what lower value of TBN, the oil is usable?
It is recommended that you should replace your oil before it reaches the 1 TBN mark as at this point the oil is considered neutral since the number of acids and bases in it are at par with one another.
This means that there is no surplus base left to further counteract acids.
Such oil is deemed unusable, henceforth plan your oil change long before this point for the safety of your engine.
What if an oil with no TBN is used?
As of now every oil in this world has some bases available but if one uses a ‘1’ TBN oil or one with no base additives then the acids included in oil as combustion byproduct will erode the metal from the upper surface of the engine.
Is higher TBN always better?
In fact yes, as the higher TBN can give a better chance of having restful long oil change intervals.
We can compare the oil change frequencies of any two oils by comparing their TBNs.
Can we add products to increase the TBN?
There are some aftermarket products available to increase the TBN of your oil, but we don’t recommend you use them as they can change the ratio of additives in your oil.
This will decrease the efficiency and effectiveness of your motor oil.
Hence always choose a genuine brand of motor oil with higher TBN.
Role of Sulphur in fuel on the TBN of engine oil
The fuels with a higher amount of Sulphur available inside them are responsible for producing Sulfuric acid when they get oxidized.
The higher the amount, the more the acid will be produced.
This will readily decrease the TBN of the engine oil and such fuels must be avoided.