Optical diagnostic methods for the study of fuel fouling

An experimental study of fuel fouling using optical measurement methods was performed. These measurements included absorption from 350 to 750 nm, scattering at 514.5 nm, and fluorescence using a probe wavelength of 514.5 nm. Measurements were performed using a constant-temperature heating system which exited into an optical cell. Each of the measurements proved useful in monitoring changes in the test fuel, JP-4, at test temperatures up to 775 K and pressures of 400 psig. Absorption measurements demonstrated both molecular changes in the fuel composition and a marked increase in the particulate present in the flow as a result of thermal stress. Scattering measurements indicated room temperature fuel to contain particulate with average diameters greater than 0.1 mu m while thermally stressed fuel contained much larger concentrations of particulate with sizes below 0.06 mu m. This work clearly illustrates the possibilities of using optical methods for monitoring the fuel fouling process.