Survey of Optical Diagnostic Methods for the Study of Fuel Fouling

摘要

An experimental study of fuel fouling using optical measurement methods wasperformed. 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 at temperatures between ambient and 860 K indicated dramatic changes in the thermally stressed fuel. These changes included indications of both molecular changes in the fuel composition and a dramatic increase in the particulate present in the flow. Relative kinetic behavior for the absorption measurement indicated that both temperature and residence time were controlling variables in the fouling process. Arrhenius plots of the absorption results illustrated that the fouling behavior could be grouped into two constant slope regions with a transition region near 525 K. Scattering measurements indicated room temperature fuel to contain particulate with average diameters greater than 0.1 micrometer while thermally stresses fuel contained much larger concentrations of particulate with sizes below 0.06 micrometer. Fluorescence signal intensities behaved, over the experimental temperature range in a manner similar to scattering intensities and displayed significant variations in spectral structure with temperature. This work clearly illustrates the possibilities of using optical methods for monitoring the fuel fouling process.