Mapping of Trace Hydrocarbon Concentrations in Two-Dimensional Flames Using Single-Photon Photoionization Mass Spectrometry

Single-photon photoionization mass spectrometry (SPPI-MS) with a vacuum ultraviolet laser beam at 118 nm has been used to quantify trace hydrocarbons sampled with a quartz microprobe from an axisymmetric nonpremixed methane/air jet flame. More than 20 C3−C12 hydrocarbons were detected, including linear species, single-ring aromatics, and two- or three-ring polynuclear aromatic hydrocarbons. For each of these species, high-resolution two-dimensional concentration maps were obtained that are suitable for comparison with detailed computer models of aromatic hydrocarbon formation and growth. Preliminary comparison with such a model indicates that the sampling process accurately captures the spatial structure of the flame. In general, the results show that the broad-band sensitivity, part-per-million detection limits, negligible ion fragmentation, and rapid data acquisition rate of SPPI-MS make it an ideal technique for studying the complex hydrocarbon chemistry that occurs in flames.