- Author
- Norton, T. S. | Smyth, K. C.
- Title
- Laser-Induced Fluorescence of CH in a Laminar CH4/Air Diffusion Flame: Implications for Diagnostic Measurements and Analysis of Chemical Rates.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Journal
- Combustion Science and Technology, Vol. 76, 1-20, 1991
- Keywords
- lasers | fluorescence | laminar flames | diffusion flames | radicals
- Abstract
- Relative CH radical concentration profiels have been measured in a laminar, co-flowing methane/air diffusion flame using laser-induced fluorescence from the (0,0) band of the [equation] transition. CH has the narrowest profiel of any species yet measured in this flame. The CH peak does not coincide with the position of the OH and temperature maxima, but appears on the fuel-rich side, between the peak concentrations of hydrogen atoms and methyl radicals. If CH fluorescnce is detected with a narrow bandpass dielectric filter, rather than using amonochromator, severe interference attributed to fluorescence from polycyclic aromatic hydrocarbons (PAH) is observed. The CH concentration decreased, while PAH fluorescence interference increases rapidly with height above the burner. Implications for CH imaging experiments in turbulent diffusion flames are discussed. The net chemical production/destruction rate of CH is determined as a function of flame poisition at a height H of 9 mm above the burner. This CH production rate profile is used to derive a relative mole franction profile for triplet methylene [equation]. The concentration ratio [equation] is found to be 13-300, where the major source of uncertainty is the reaction rate of [equation]. Maximum concentrations of the CHx radicals are not well established in this flame. However, if the derived [equation] ratio is combined with the calculated value of 25 ppm for [equation] from Puri et al. (1987), one estimates that the peak CH mole fraction lies between 0.08 and 2 ppm at H = 9 mm.