Development of Laser Diagnostic Method for Nano-PM Precursor Formed in Flames

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Laser induced fluorescence(LIF) method for the measurement of PAHs(Polycyclic Aromatic Hydrocarbons) in diffusion flames was developed. A KrF excimer laser and a dye-laser pumped by a XeF excimer laser were used to excite the PAHs molecules. Two-dimensional images of PAHs concentrations in the flame could be obtained by using the temporally resolved LIF method. From the data of emission spectra of PAH vapors, it was found that the peak wavelength in the emission spectrum of LIF shifted to the longer wavelength side with an increase of PAH carbon numbers. By using of this data, carbon numbers of PAH in a diffusion flame was presumed. It was confirmed that the carbon numbers of PAHs in the diffusion flame increased with approaching to the flame surface. The maximum carbon number was about 26 at the layer close to the flame surface of laminar diffusion flames.