Spectroscopic Measurement of Used Lubricating Oil Quality

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Abstract
Used lubricating oils have been examined by a number of spectroscopic techniques to assess whether it might be possible to improve turn-around time for laboratory analyses or to develop a simple oil quality sensor which could be used in a service workshop. Investigation shows that the development of an oil quality sensor based on discrete wavenumber measurements in the mid-infrared region would not be warranted, but heptane-insolubles can be estimated from a single measurement in the near-infrared region, and this could form the basis of a simple sensor. Considerable information about the quality of a used oil is available through a thorough examination of its mid-infrared spectrum. Use of the computer program CIRCOM, which employs factor analysis followed by multiple linear regression, allowed useful correlations to be obtained for n-heptane—insolubles level and viscosity and total base number of the oil sample. This supplements and extends the previously described methods for obtaining information such as fuel and water levels by IR analysis.