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70 . OilExpress System User's Guide
Background to Used Oil Analysis
Infrared Absorption
The chemical bonds within organic molecules are in a state of continual vibration, with bonds
stretching and contracting as well as bending relative to each other. When an infrared beam
falls on a molecule, waves of specific frequencies are absorbed from the beam by the
molecule. The actual frequencies absorbed depend on the types of bonds present in the
molecule structure. Chemical bonds within a molecule are said to exhibit “characteristic
infrared absorptions”.
A record of the frequencies at which absorption takes place for an organic compound is
called its infrared spectrum. An infrared spectrum of a compound will reveal information
about molecular structure as the existence of specific groups of atoms may be confirmed
from the presence of their characteristic absorptions.
Why Analyze Used Oils?
Infrared analysis of used oils provides critical information regarding the state of the lubricant
itself and the engine from which it comes.
Used oil analysis provides a great deal of information in two areas:
1. The physical condition of the lubricating oil, such as its viscosity, neutralization number,
or level of contamination.
2. The condition of the component or system from which the sample was taken.
The presence of chemical degradation products due to oxidation, nitration, sulfate formation,
ester breakdown, and anti-wear additive depletion, and contaminants such as soot, water,
ethylene glycol and unburned fuel is used to measure the degradation of the oil.
Analyzing used oil samples and comparing the resulting spectrum (showing characteristic
absorptions of the degradation products, oil and contaminants) with an unused oil spectrum
contained in a “new oil” library accurately monitors the chemical degradation of engine
lubricants.