Study And Application Of PAHs Spectral Analysis Method Based On Laser Induced Fluorescence

PAHs is a carcinogenic toxic substance,which is often produced in the incomplete combustion of hydrocarbon fuels.The study on the fluorescence characteristics of PAHs and its evolution rule in flame is of guiding significance for the treatment of exhaust gas pollution.In this paper,the fluorescence characteristics of gas-phase PAHs and flame-formed PAHs were studied based on LIF technique,a non-invasive measurement method with high temporal and spatial resolution,combined with heating furnace system and burner system.The temperature dependence,concentration dependence and superposition regulation of gas-phase PAHs were studied.Based on these,a spectral analysis method for the complex PAH mixtures was constructed to optimize the traditional LIF technique.Chemkin Pro software and KAUST2 mechanism were used to simulate the PAH concentrations in flames,and the experimental results were further explained.The main results are as follows:?1?Temperature and concentration dependence of phase PAHs fluorescence spectrum:In terms of temperature,as the temperature gradually increased,the shape of PAHs spectrum gradually changes,and the phenomenon of red shift occurs.The fluorescence intensity of PAHs also decreased with the increase of temperature.In terms of concentration,with the increase of PAHs concentration,the fluorescence intensity of PAHs increased linearly,while the spectral shape did not change.?2?PAH fluorescence spectral analysis method:Based on the experimental data and theoretical formula,the extrapolation formula of PAHs fluorescence intensity and temperature was constructed,and PAHs fluorescence spectral shape extrapolation method was combined to establish the PAHs fluorescence spectral temperature extrapolation model.The fluorescence of PAHs mixed solution was tested and it was found that the fluorescence spectra of different types of PAHs could be linearly superimposed.?3?Fluorescence characteristics of PAHs in flame:The fluorescence intensity of PAHs in laminar premix C₂H₄ flame increases gradually with the increase of flame height,and the fluorescence spectral shape remains basically unchanged.With the increase of flame temperature,the red shift of PAHs fluorescence spectrum occurs,and the fluorescence intensity gradually decreases with the increase of temperature,and its attenuation rate is higher than that of gas phase PAHs fluorescence intensity,indicating that the rise of temperature will inhibit the generation of PAHs in the flame.The trend of simulation results is highly consistent with the experimental results,which verifies the reliability of the mechanism.According to the calculated ratio of PAHs concentration,the spectral fitting of gas phase PAHs was carried out,which fitted with the rising edge height of flame spectrum and verified the scientific of the spectral analysis method.