Fluorescence spectroscopy of aromatic species produced in rich premixed ethylene flames

The fluorescence spectra of the condensed species (CS) collected in the soo t inception region of a rich premixed laminar ethylene/oxygen flame have be en measured by excitation in the UV at 266 and 355 nm excitation wavelength . The contribution of the most abundant polycyclic aromatic hydrocarbons (P AH) to the CS fluorescence has been evaluated in order to attribute the CS fluorescence at different emission wavelengths to specific aromatic structu res. The fluorescence peaks detected in the UV region of the CS fluorescenc e spectrum was found to be mainly due to a typical PAH like fluorene, that is, the most fluorescent one among the PAH analyzed in the CS by chromatogr aphic analysis. The CS exhibited the larger emission in the visible where t he PAH contribution has been shown to be negligible and other fluorescing a romatic species, not identified by chromatographic analysis of the CS, have to be considered responsible for the visible fluorescence. Laser induced f luorescence (LIF) flame measurements excited at 266 nm and detected at two selected wavelengths (310 and 410 nm) have been performed along the flame a xis and compared with the CS fluorescence intensity. The LIF and CS fluores cence signals show quite similar axial trends demonstrating that the LIF si gnals are related to CS fluorescence. In particular, the LIF fluorescence s ignals detected in the UV could be attributed to the PAH fluorescence where as the unidentified species contained in the CS can be followed by LIF dete ction in the visible region. (C) 2001 Elsevier Science Ltd. All rights rese rved.