Marine Analysis Program

TBN Total Base Number

The Base Number (BN) is a measure of the alkalinity of the oil. It is a measure of the effective additive content and thus reflects the oil’s detergent, dispersant and anti-rust properties. The engine manufacturer normally specifies the minimum acceptable BN. A significant decrease may be caused by excessive degradation, a change in the sulphur content of the fuel or by top-up with different oil. The determination of the Base Number, either according to ASTM D2896 method or following an internal procedure, is based on the measurement of the base constituents in both fresh oils and used oils by potentiometric titration with Perchloric acid in glacial acetic acid. The normal range for this application of the method is 0.10 – 300.0 mg KOH/g.

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