Testing the degradation of lubricants using normalized time-resolved fluorescence spectral subtraction

A new method of Normalized Time-Resolved Fluorescence Spectral Subtraction (NTRFSS) was used to determine the degradation of lubricating oils. The method relied on measuring the laser-induced time-resolved fluorescence (TRF) spectra of the degraded oils at successive narrow time-gates within the temporal span of the laser pulse and subtracting them from the corresponding spectra of their neat samples. Contour maps were then constructed from the resulting TRF spectral subtraction to act as accurate indicators of the degradation conditions of the oils. Tests were conducted on an automobile lubricant at different degradation stages and also on a gas turbine lubricant. The results showed that the shapes of the NTRFSS contours were very sensitive to the degradation condition and also to the type of the lubricant used. The method is totally non-destructive and provides an enhancement over our recently introduced technique¹ in terms of the distinguishing ability between degraded oils.