Typically used for testing crankcase oils, base number (BN) is a measure of a reserve alkalinity of a lubricant. It is a measurement of basicity that is expressed as the equivalent number of milligrams of potassium hydroxide per gram of oil sample (mg KOH/g) that is required to titrate and neutralise the acidic components in a sample, in this case oil.
Through the addition of acid to a known quantity of sample. The more acid required, the more basic the sample and the higher the base number.
The test is relevant to internal combustion engines due to the acidic by-products of combustion generated when petrol and diesel fuel are burned (such as sulfuric acid).
BN is often used in measurement of additives and detergent that remain active in the oil, which are in place to control or limit combustion by-products.
Like the acid number, the BN can be improved in used oils by the appropriate use of additives and topping up the oil reservoir to dilute the oil.
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