What gas engine oil parameters are monitored during the lifetime of the oil?

A frequent monitoring of a gas engine oil is essential to determine drain interval and to protect the engine. The main parameters that are monitored are the following : 

● TBN: Total Base Number (mg KOH/g)
It represents the reserve of alkalinity of the oil. This reserve is consumed as it neutralizes the acids formed during combustion.
Manufacturers generally consider that TBN should remain higher than 50% of the initial value.

● AN: Acid Number (mg KOH/g)
Its increase is the result of the ageing of the oil.
Manufacturers generally consider that the AN should remain below the initial value of the fresh oil + 2.5 mgKOH/g.

● Viscosity (mm²/s)
Oil thickening can be the result of an abnormal temperature rise, or of an advanced state of oxidation of the oil. Viscosity drop can be caused by fuel dilution (for dual-fuel engines).
SAE 40 limits are applied.

● IR oxi meas (A/cm)
Measurement of gross oil oxidation value by infrared spectrum analysis.

● IR oxi net (A/cm)
Calculation of real oil oxidation value, by comparison between fresh oil initial oxidation and gross oil oxidation values.

● IR nitr net (A/cm)
Calculation of real oil nitration value, by comparison between fresh oil initial nitration and gross oil nitration values.

● ipH: pH initial
It is a pH measurement adapted to non-aqueous fluids.