Temporally Resolved Species Measurements from an Acoustically Forced Methane/Nitrogen Axi- Symmetric Flame Using Pulsed, Quartz Microprobe Gas Extraction Followed By Electron Impact Mass Spectrometry

摘要

Hydrocarbon growth processes in flames are important both to the understanding of soot production from combustion systems and for the development of continuous processes for the manufacture of carbon-based materials. In addition to direct health effects of combustion-generated soot and polyaromatic hydrocarbons, the temperature decrease due to radiative losses can affect flame length and other temperature-dependent processes such as the formation of NO_x. Similarly, in flames in which substantial fractions of fuel carbon are converted to soot, a shift in the local H_2/H_2O and CO/CO_2 conversion ratio can affect the local heat release and the local temperature. Time-varying flames are an important intermediate between laminar and turbulent combustion because they exhibit a larger range of combustion conditions than those observed in steady flames. Such flames may give insights into a variety of chemistry-flowfield interactions important in turbulent combustion - all of which occur in a reproducible flame cycle. For the past decade, several groups have studied time-varying, methane flames burning in air formed by imposing a periodic fluctuation to the fuel flow rate of a steady flame. The fuel for these flames has been "neat" methane, or diluted with either nitrogen or air. If the fuel flow perturbation is sufficiently large, these flames formed are distinguished by the formation of axi-symmetric time-dependent, large-scale, vortical structures caused by buoyancy-driven flow instabilities.