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A combined ab initio and photoionization mass spectrometric study of polyynes in fuel-rich flames

Physical Chemistry Chemical Physics

Hansen, Nils H.; Klippenstein, S.J.; Westmoreland, P.R.; Kasper, Tina K.; Kohse-Höinghaus, K.; Wang, J.; Cool, T.A.

Polyynic structures in fuel-rich low-pressure flames are observed using VUV photoionization molecular-beam mass spectrometry. High-level ab initio calculations of ionization energies for C2nH2 (n = 1-5) and partially hydrogenated CnH4 (n = 7-8) polyynes are compared with photoionization efficiency measurements in flames fuelled by allene, propyne, and cyclopentene. C2nH2 (n = 1-5) intermediates are unambiguously identified, while HC≡C-C≡C-CH=C= CH2, HC≡C-C≡C-C≡C-CH=CH2 (vinyltriacetylene) and HC≡C-C≡C-CH=CH-C≡CH are likely to contribute to the C7H4 and C8H4 signals. Mole fraction profiles as a function of distance from the burner are presented. C7H4 and C8H4 isomers are likely to be formed by reactions of C2H and C4H radicals but other plausible formation pathways are also discussed. Heats of formation and ionization energies of several combustion intermediates have been determined for the first time. © the Owner Societies.

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TYPE Conference YEAR 2008
ScopusOSTI

MBMS investigation of a laminar tetrahydrofuran flame

Western States Section/Combustion Institute Fall Meeting 2007

Kasper, T.; Hansen, Nils H.; Wang, J.; Yang, B.; Cool, T.A.; Westmoreland, P.R.

Cyclic ethers, like tetrahydrofuran (THF), are formed during the autoignition of alkanes and subsequently influence their combustion chemistry. To learn more about the oxidation chemistry of these ether intermediates, a fuel-rich THF flame (π = 1.75) has been studied using the versatile technique of flame-sampling Molecular Beam Mass Spectrometry (MBMS) in combination with single-photon ionization. Several cyclic intermediates which are potentially formed by dehydrogenation of the fuel are identified by their ionization energies. Ethylene, propene, ketene and formaldehyde are major stable decomposition products of THF and their mole fraction profiles are presented. Detected oxygenated species include ethenol, acetaldehyde and propanal. Despite the fuel-rich conditions, the concentrations of benzene and other aromatic hydrocarbons are near the detection limit.

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TYPE Conference YEAR 2007
ScopusOSTI

Photoionization mass spectrometric studies and modeling of fuel-rich allene and propyne flames

Proceedings of the Combustion Institute

Hansen, Nils H.; Miller, James A.; Taatjes, Craig A.; Wang, Juan; Cool, Terrill A.; Law, Matthew E.; Westmoreland, Phillip R.

Flame-sampling photoionization mass spectrometry is used for measurements of the absolute molar composition of fuel-rich (φ = 1.8) low-pressure laminar flames of allene and propyne. The experiment combines molecular-beam mass spectrometry with photoionization by tunable vacuum-ultraviolet synchrotron radiation. This approach provides selective detection of individual isomers and unambiguous identifications of other flame species of near-equal mass by near threshold photoionization efficiency measurements. Mole fraction profiles for more than 30 flame species with ion masses ranging from 2 to 78 are presented. The isomeric composition is resolved for most intermediates, for example, mole fraction profiles are presented for both benzene and the fulvene isomer. The results are compared with predictions based on current kinetic models. The mole fractions of the major species are predicted quite accurately, however, some discrepancies are observed for minor species. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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TYPE Conference YEAR 2007
ScopusOSTI

The influence of ethanol addition on premixed fuel-rich propene-oxygen-argon flames

Proceedings of the Combustion Institute

Kohse-Höinghaus, Katharina; Oßwald, Patrick; Struckmeier, Ulf; Kasper, Tina; Hansen, Nils H.; Taatjes, Craig A.; Wang, Juan; Cool, Terrill A.; Gon, Saugata; Westmoreland, Phillip R.

The role of ethanol as a fuel additive was investigated in a fuel-rich, non-sooting (C/O = 0.77) flat premixed propene-oxygen-argon flame at 50 mbar (5 kPa). Mole fractions of stable and radical species were derived using two different in situ molecular beam mass spectrometry (MBMS) set-ups, one located in Bielefeld using electron impact ionization (EI), and the other at the Advanced Light Source (ALS) at Berkeley using vacuum UV photoionization (VUV-PI) with synchrotron radiation. A rich propene flame, previously studied in detail experimentally and with flame model calculations, was chosen as the base flame. Addition of ethanol is believed to reduce the concentrations of benzene and small aromatic compounds, while augmenting the formation of other regulated air toxics such as aldehydes. To study the chemical pathways responsible for these effects, quantitative concentrations of about 35 species were determined from both experiments. This is also the first time that a detailed comparison of quantitative species concentrations from these independent MBMS set-ups is available. Effects of ethanol addition on the species pool are discussed with special attention on benzene precursor chemistry and aldehyde formation. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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TYPE Conference YEAR 2007
ScopusOSTI
Results 76–100 of 104
Results 76–100 of 104