What is “equilibrium TBN” of a Marine Engine oil?
Once new oil is put into service, the TBN will either slowly rise or fall from its new value to a value known as the “equilibrium TBN”. This TBN level will remain fairly constant until the engine operation conditions change. The fuel sulphur content and the oil consumption are among the most influencing factors for the equilibrium TBN. For simplicity, we can say that a higher sulphur fuel will cause a fall in TBN; an increase of the oil consumption would cause the TBN value to rise while a reduction of the oil consumption would result in a lower equilibrium TBN. Many engine OEMs specify the minimum equilibrium TBN of the used lubricant, in addition to other parameters that should be carefully monitored in order to ensure the oil is in satisfactory condition.
