Monitoring of fuel consumption and aromatic formation by fluorescence techniques in spray flames

The large presence of light aromatic compounds in distillate fossil fuels should allow, in line of principle, to follow the fuel consumption and/or the presence of unburned fuel in a high temperature environment like a burner or the exhaust of combustion systems by exploiting the high fluorescence emission of aromatic fuel components. To this aim an uv-excited fluorescence source has to be used since the aromatic fuel components are strongly fluorescing in the uv region of the emission spectrum. In this work uv-excited Laser Induced Fluorescence (LIF) diagnostics was applied to spray flames of kerosene in order to follow the fuel consumption and the formation of aromatic species. A strong uv signal was detected in the spray region of the flame that presented a shape similar to that found in the LIF spectra preliminary measured on the cold spray and in the room-temperature fluorescence of fuel solutions. The decrease of uv signal along the spray flame region was associated to the consumption of the fuel, but more difficult seems to be the attribution of a broad visible emission, that is present downstream of the flame. The visible emission feature could be assigned to flame-formed PAH species contained in the high molecular weight species, hypothesizing that their fluorescence spectra are shifted toward the visible for effect of the high temperature flame environment.