PerkinElmer OilExpress 4, User Manual

Page: 13 / 152

Introduction . 13
Antioxidant
Pheonolic antioxidant compounds are often used in turbine lubricants. Depletion of
antioxidant is followed by a rapid increase in the rate of oxidation.
Common Contaminants
Soot
Soot particles result from the incomplete combustion of fuel and, since they are too small to
be removed by the filter, remain suspended in the oil. Soot builds up continuously until it
reaches an unacceptable level; that level depends on the type of engine and lubricant. Diesel
oils tolerate higher soot levels than gasoline oils. The rate of soot build-up depends on
engine design, type of fuel and operating conditions. A high soot value may indicate poor
combustion due to an incorrect fuel/air ratio, a clogged air filter or an over-extended oil
change period.
Water and glycol
The presence of water and glycol in crankcase oil indicate a leak from the cooling system. It
is essential to detect such a problem early to avoid a serious failure. The presence of water
alone does not necessarily indicate a coolant problem, but may result from condensation due
to a low operating temperature.
Water contamination can also occur in hydraulic systems through leakage or condensation in
reservoirs.
Unburned fuel
The presence of fuel in the oil indicates poor combustion due to an incorrect fuel/air ratio, a
clogged air filter or an ignition problem. It may also indicate an over-extended oil change period.
NOTE: The fuel measurement depends not only on the level of contamination, but also on
the aromatic hydrocarbon content of the fuel. The aromatic content of fuels varies
with location and season, so it may be appropriate to perform a calibration with the
fuel being used.
Standard Methods for Lubricants Analysis by FT-IR
Spectral-subtraction and direct-trending methods
Because of the wide variety of lubricating oils available, it is essential to consider the oil type
when interpreting the spectrum. The changes due to wear may be quite subtle compared to
the differences between different oils. One approach to this problem is to measure the
spectrum of the unused oil (if this is available) and subtract this from the used oil.