Direct Sampling Mass Spectrometry for the Study of Polynuclear Aromatic Hydrocarbons and Other Combustion Intermediates and Products
Open AccessThe goal of this work is the analysis of combustion intermediates and products from non-premixed flames, in particular polynuclear aromatic hydrocarbons (PAH). These molecules have often been proposed as key intermediates in the pathways that lead from fuel to soot formation. Identification and quantification of these species from combustion systems is critical for the validation of computational simulations which model soot formation in flames. Generally, PAH and small hydrocarbons are examined through microprobe extraction from the flame followed by mass spectrometry. In this work, electron impact mass spectrometry (EI/MS) with an ionization energy of 70 eV was used. This technique is shown to provide sub part-per-million sensitivity of a large range of major and minor carbon-containing species ranging in size from C3 to C12 hydrocarbons. The near real-time sampling and analysis time and the relatively high sensitivity make this technique preferable to other extractive approaches of comparable flame measurements.The microprobe extraction 70 eV EI/MS technique was employed to examine a host of combustion systems. The goal of these studies is two-fold. The first is to characterize base-case (unperturbed) flames through the measurement of major and minor species concentrations. The second goal of these studies is to analyze the effects of perturbations to the fuel of the base-case flames. For instance, the measurements shown in Chapter 6 represent the first time-resolved measurements of PAH from flickering flames reported in the literature. Chapter 7 presents measurements from a pyridine-doped methane flame. Pyridine is a fuel-bound-nitrogen containing molecule found in coal and its derivatives. The combustion of such fuels is associated with increased production of NOx, a toxic by-product of combustion important in the formation of acid rain and photochemical smog.Chapter 8 presents measurements from a methyl butanoate doped methane flame. Methyl butanoate has recently been proposed as a surrogate for the analysis of biodiesel combustion and contains all of the functional groups of a more complex biodiesel. The results presented in Chapter 8 show that consumption of methyl butanoate is initiated by unimolecular decomposition.
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