Extinction Measurements Near 3.0 Micrometers in Nitrogen-diluted, Ethylene, Non-Premixed Flames

摘要

Several recent studies have reported substantial aliphatic composition in collected nascent particulate from rich flames. These results would have a profound impact on a conventional view of soot nucleation that begins with the agglomeration of polynuclear aromatic hydrocarbons. To rule out sampling artifacts that might accompany sample extraction, the current study was initiated to explore an in situ optical measurement of extinction in the carbon-hydrogen stretching fingerprint region using an external-cavity, quantum cascade laser operating between 2980 and 3170 cm~(-1). The target system for this work is a nitrogen-diluted, ethylene air flame supported on a "Yale", co-annular burner. This work uses a similar optical train as has been reported for recent work from our laboratory in which visible light from a supercontinuum light source was employed to determine the optical band gap of soot in this and other non-premixed flame systems. The spectral region of the mid infrared laser spans frequencies diagnostic for carbon-hydrogen stretching vibrations typical of single, double, and tripled bonded carbon as well as those typical of aromatic C-H bonds.