Method for characterization of petroleum oils using normalized time-resolved fluorescence spectra

A method for monitoring the degradation over time petroleum lubricants and transformer oils using normalized time-resolved fluorescence comprising the following steps:

• exposing an unknown petroleum lubricant or transformer oil sample to a pulse of ultraviolet laser radiation;
• measuring the intensities of resulting fluorescence over the spectrum of wavelengths of light from said petroleum lubricant or transformer oil sample at specific narrow time gates within the temporal response of said laser pulse to form a time-resolved spectrum;
• normalizing said time-resolved spectrum at a particular emission wavelength;
• plotting said time-resolved spectrum in contours as functions of wavelength and time simultaneously;
• comparing the resultant plots of said plotting step with those of similar samples taken at known levels of degradation;
• and
• characterizing said unknown sample based on similarity of said resultant plots with those of a particular known sample.

A method for estimation of the ∘API gravity of crude oils using the shapes of time-resolved fluorescence spectra comprising the following steps:

• exposing an unknown crude oil sample to a pulse of ultraviolet laser radiation;
• measuring the intensity of resulting fluorescence over the spectrum of wavelengths of light from said crude oil sample at a specific narrow time gate within the temporal response of said laser pulse to form a time-resolved spectrum;
• plotting said time-resolved spectrum;
• determining the ratio of the area under a first segment off said time-resolved spectrum to at least a second segment of said time-resolved spectrum;
• and
• determining the ∘API gravity of said sample by comparing said ratio to a plot of ratios as a function of ∘API gravities for known crude oils.