The relation between ultraviolet-excited fluorescence spectroscopy and aromatic species formed in rich laminar ethylene flames

The exploitation of fluorescence techniques for the characterization of aro matic pollutants formed in combustion processes needs a reliable interpreta tion for the assignment of fluorescence emission to specific products. To t his aim, ultraviolet-excited LIF (laser-induced fluorescence) spectra were measured in premixed rich ethylene/oxygen flames having a different PAH mas s loading as verified by sampling and chomatographic analysis of the conden sed species produced along the flames. Fluorescence emission in the ultraviolet was mainly found in the flames whe re PAH formation is relatively low indicating that ultraviolet-fluorescence emission is not related to PAH species. On the opposite, broad visible emi ssion features became prevalent in PAM-rich flames suggesting that the fluo rescence of PAH species could be shifted toward the visible for effect of t he high-temperature flame environment. In alternative to this hypothesis th e visible fluorescence could be due to the heavier unidentified part of the condensed species whose fluorescence emission is shifted toward the visibl e. (C) 2001 by The Combustion Institute.