Temporally-Resolved Measurements of PAH Concentrations in an Acoustically-Forced Methane/Air, Non-Premixed Flame

摘要

Polynuclear aromatic hydrocarbons (PAH) have often been invoked as important intermediates in the chemistrythat leads from simple fuels to carbonaceous particulate matter in flames. The goal of this work is to present anapproach for the analysis of sample mixtures drawn from the molecular growth region of both steady andacoustically forced flames that can report directly mixing ratios of several substituted one and two ring aromaticcompounds. Acoustically forced flames are an important intermediate between laminar and turbulent combustionbecause they exhibit a larger range of combustion conditions than those observed in steady flames. Thus, theseflames may give insights into a variety of chemistry-flowfield interactions important in turbulent combustion - allof which occur in a reproducible flame cycle. Most of the measurements of flame species in these unsteadyflames have been accomplished by in situ, laser-based methods. Unfortunately, it has not been possible to makespecies-selective determinations of PAH concentrations using optical techniques. In this paper, spatially andtemporally resolved concentrations of aromatic concentrations are presented for a 10 Hz, acoustically forced,methane/air non-premixed flame supported on an axially symmetric diffusion burner. Samples were withdrawnfrom the flame using a modified quartz microprobe designed to minimize dead volume in the probe during thesampling event. Valve opening and closing was synced to the forcing waveform. Extracted gases were analyzedusing direct sampling mass spectrometry.