UV-visible spectroscopy of organic carbon particulate sampled from ethylene/air flames

A systematic comparison of spectra obtained with extra and in situ diagnost ics in the soot preinception region of rich, premixed ethylene air flames s uggests that combustion generated organic carbon (OC) particulate can be ex tracted from flames and isolated from other flame material for further chem ical analysis. Both the trend with height above the burner and the form of UV fluorescence and absorption spectra from extra situ sampled material cap tured in water agree with those measured in situ. These results show that t he OC particulate formed in flames is partially water soluble. However, the collection efficiency can be increased using less polar solvents, like ace tonitrile and dichloromethane. The fluorescence spectra from the water samp les are comprised both a naphthalene-like component and a broad band UV flu orescence component similar to that observed in situ which is attributed to flame generated OC particulate. The broad band UV fluorescence centered ar ound 320 nm is also observed very early in flames and does not change consi derably with increasing flame residence time. These results support previou s hypotheses that the UV broad band fluorescence is from carbonaceous mater ial comprised two-ring aromatics, formed earlier than soot in the flame, an d is still present along with soot at higher heights or flame residence tim es. (C) 2001 Elsevier Science Ltd. All rights reserved.