Laser Excited Fluorescence Measurements in Spray Oil Flames for the Detection of Polycyclic Aromatic Hydrocarbons and Soot

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Abstract
Broad band fluorescence emissions excited by a c.w. argon ion laser have been measured in the initial zone of a spray flame of light oil Previous studies by other authors on gaseous flames have suggested that the polycyclic aromatic hydrocarbons (PAH) were responsible of this emission, however, the presence and properties of laser excited fluorescence in flames produced by liquid fuels have not been the object of study Measurements of the elastic scattered light analyzed in the vertical and horizontal plane and thermocouple temperatures were also carried out in order to characterize the spatial distribution of the fuel droplets and soot particles Two flames with different tangentiality of the fluid dynamic pattern were investigated and the presence of PAH was detected in well characterized regions The analysis of the fluorescence coefficient and the assessment of the PAH concentrations on isothermal and burning sprays showed that the main contribution to the fluorescence was due to the product formed in the pyrolytic process more than the PAH present in the oil The highest concentration of PAHs was found in low temperature pyrolysis regions which are not necessarily coincident with the regions of maximum production of soot particles and which seem to require a higher temperature level.