A Study on Thermo-Acoustic Instability of Downward-Propagating Hydrocarbon Flames in a Tube

A pair of laminar, premixed, CH4–O2 flames above 2000 K at atmospheric pressure, one fuel-rich (FR) and the other fuel-lean (FL), were doped with ~10−6 mol fraction of the second-row transition metals Y, Zr, Nb, and Mo. Since these hydrocarbon flames contain natural ionization, metallic ions were produced in the flames by the chemical ionization (CI) of metallic neutral species, primarily by H3O+ and OH− as CI sources. Both positive and negative ions of the metals were observed as profiles of ion concentration versus distance along the flame axis by sampling the flames through a nozzle into a mass spectrometer. For yttrium, the observed ions include the YO+•nH2O (n = 0–3) series, and Y(OH)4−. With zirconium, they include the ZrO(OH)+•nH2O (n = 0–2) series, and ZrO(OH)3−. Those observed with niobium were the cations Nb(OH)3+ and Nb(OH)4+, and the single anion NbO2(OH)2−. For molybdenum, they include the cations MoO(OH)2+ and MoO(OH)3+, and the anions MoO3− and MoO3(OH)−. Not every ion was observed in each flame; the FL flame tended to favour the ions in higher oxidation states. Also, flame ions in higher oxidation states were emphasized for these second-row transition metals compared with their first-row counterparts. Some ions written as members of hydrate series may have structures different from those of simple hydrates; e.g., YO+•H2O = Y(OH)2+ and ZrO(OH)+•H2O = Zr(OH)3+, etc. The ion chemistry for the production of these ions by CI in flames is discussed in detail. Keywords: transition metals, ions, flame, gas phase, negative ions.

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Soot formation in chlorine-hydrocarbon flames

Combustion Explosion and Shock Waves ◽

10.1007/bf00749188 ◽

1988 ◽

Vol 24 (2) ◽

pp. 199-201 ◽

Cited By ~ 2

Author(s):

A. V. Steblev ◽

Yu. E. Frolov

Keyword(s):

Soot Formation ◽

Hydrocarbon Flames

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Measurements of the Collisionally Quenched Lifetime of CO in Hydrocarbon Flames

Applied Spectroscopy ◽

10.1366/0003702944029514 ◽

1994 ◽

Vol 48 (9) ◽

pp. 1118-1124 ◽

Cited By ~ 17

Author(s):

Sara Agrup ◽

Marcus Aldén

Keyword(s):

Laser Induced Fluorescence ◽

Polyaromatic Hydrocarbon ◽

Time Decay ◽

Collisional Quenching ◽

Time Resolved ◽

Hydrocarbon Flames ◽

Effective Lifetime ◽

Ethylene Flame ◽

Oxygen Flame ◽

Different Parts

Time-resolved laser-induced fluorescence (LIF) from CO molecules in hydrocarbon flames was studied. Collisional quenching constants were evaluated on the basis of the exponential decays. Effective lifetime in a methane/oxygen flame was observed to vary between 250 and 400 ps depending on the position within the flame, and from 400 to 600 ps in the non-sooty parts of an ethylene/air flame. Fluorescence, constituting simultaneous spatially and temporally resolved decays, was also registered from various sections along a laser beam that probed different parts of the flame. Spectral recordings revealed not only the expected CO peaks but also, in the ethylene flame, laser-induced emission from C2 Swan bands and from polyaromatic hydrocarbon (PAH) emission that affected the fluorescence time decay in the sooty part of the flame.

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Dual-broadband rotational CARS thermometry in the product gas of hydrocarbon flames

Proceedings of the Combustion Institute ◽

10.1016/j.proci.2004.08.043 ◽

2005 ◽

Vol 30 (1) ◽

pp. 1673-1680 ◽

Cited By ~ 48

Author(s):

Fredrik Vestin ◽

Mikael Afzelius ◽

Christian Brackmann ◽

Per-Erik Bengtsson

Keyword(s):

Hydrocarbon Flames ◽

Product Gas

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The effect of diluent gases on ion formation in hydrocarbon flames

Canadian Journal of Chemistry ◽

10.1139/v78-374 ◽

1978 ◽

Vol 56 (17) ◽

pp. 2273-2277 ◽

Cited By ~ 4

Author(s):

Brenda L. Chawner ◽

Arthur T. Blades

Keyword(s):

Diffusion Flame ◽

Formation Process ◽

Hydrocarbon Flames ◽

Ion Formation ◽

Air Diffusion

It has been demonstrated that the addition of N2, CO, Ne, Ar, Kr, Xe, CO2, and CF4 to a H2-air diffusion flame containing He and traces of CH4 enhances the level of ion formation. This enhancement is proportional to the concentration of both CH4 and the diluent gas, consistent with the proposition that the diluent gas participates in the ion formation process.

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Ion chemistry of transition metals in hydrocarbon flames. II. Cations of Sc, Ti, V, Cr, and Mn

Canadian Journal of Chemistry ◽

10.1139/v88-353 ◽

1988 ◽

Vol 66 (9) ◽

pp. 2219-2228 ◽

Cited By ~ 12

Author(s):

John M. Goodings ◽

Quang Tran ◽

Nicholas S. Karellas

Keyword(s):

Transition Metals ◽

Metal Atom ◽

Chemical Ionization ◽

Metallic Ions ◽

Ion Chemistry ◽

Hydrocarbon Flames ◽

Basic Series ◽

First Time ◽

Isomeric Structures

The same fuel-rich, premixed, conical, methane–oxygen flame at 2200 K and atmospheric pressure used for studies of Fe, Co, Ni, Cu, and Zn in Part I (1) is doped with the same concentration (~1 ppm) of Sc, Ti, V, Cr, and Mn to complete the first row of ten transition metals. Metallic ions of these metals and their compounds formed by chemical ionization reactions with H3O+ are observed by sampling the flame through a nozzle into a quadrupole mass spectrometer. Concentration profiles of individual and total cations are measured as a function of distance along the flame axis, and also mass spectra at a fixed point in the burnt gas. If A is the metal atom, the observed ions can be represented by four hydrate series including (a) A+•nH2O, (b) AOH+•nH2O, (c) AO+•nH2O, and (d) AO2H+•nH2O with n = 0–3 or 4, giving a maximum of four ligands around the metal atom. However, alternative isomeric structures are possible for each of the four basic series (e.g. AO+•2H2O ~ A(OH)2+•H2O ~ A(OH)3H+). The ions observed with Cr and Mn, in common with those of Fe, Co, Ni, and Cu, strongly favour series (a). On the other hand, Sc is completely different; the ions of series (c) are dominant. All four series are observed with each of Ti and V. Series (b) dominates for Ti and series (c) for V; ions from series (d) were observed for the first time. The ion chemistry of these metals is discussed in detail with emphasis on the probable chemical ionization reactions responsible for metallic ion formation. The pre-eminent role of proton transfer processes is apparent.

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