The impact of detergent chemistry on TBN retention

Abstract

AbstractHistorically, the characterisation of fresh and used diesel engine lubricants has been based on a limited number of analytical techniques. One of the most important methods of analysis has been total base number (TBN) measurement. Although TBN measurements are informative, easy, and quick, it can be misleading to base the judgement of an oil's performance solely on one criterion.This paper offers some observations from a field test, showing that some detergent types gave unacceptable performance even though the TBNs were at an acceptable level. It is hypothesised that some detergents do not effectively neutralise all acidic species present in the lubricant, thereby reserving their own base, while in fact the oil may no longer provide sufficient protection against bearing corrosion. This hypothesis is supported by bench and engine test data. It is recommended that, at a minimum, total acid number (TAN) measurements be included in any analysis, and where time and cost permit, wear metals content, oxidation, soot content, and viscosity should also be evaluated.