Gas Turbine Handbook : Principles and Practices

Accessories 103
Carbon Residue
Measures the amount of residue left after evaporation and burning
of a sample of oil under standard conditions. Distillate oils leave
less carbon residue than residual oils and most naphthenic oils leave
less carbon residue than paraffin oils.
Ash Content
Measures the ash that remains after burning a sample of oil.
Clean, straight mineral oils have zero ash content. This test is useful
for non-additive oils to detect contamination.
Emulsion Characteristics
Measures the ability of oil to separate from water. This is important
in lube oil circulating systems where contamination by water
may occur.
Oxidation Characteristics
Measures the ability of the oil to resist oxidation. All oils oxidize
and deteriorate in service. Therefore, good resistance to oxidation
should be built into the oil selected for the lube oil service.
Neutralization Number
An increase in the Neutralization Number (NV) indicates an
increase in acidity due to oxidation of the oil. To determine the NV a
used oil value must be compared with the value for the new oil.
Effective Additive
This test compares the total base number (TBN) of a used oil
sample with the TBN of the new oil. This test is used to determine
the effectiveness of the remaining additives in the oil.
Water Content
This test measures the actual water content of the oil. However,
a visual inspection for cloudiness or an opaque yellow appearance will
usually suffice to indicate the presence of water.