Flame-ion probe of the reaction zone in a CH4–O2–Ar flame with added HCN, NH3 and NO

1981 ◽  
Vol 59 (12) ◽  
pp. 1810-1818 ◽  
Author(s):  
John M. Goodings ◽  
Gary B. De Brou ◽  
Diethard K. Bohme
Keyword(s):  
Reaction Zone ◽  
Atmospheric Pressure ◽  
Protonated Form ◽  
Good Evidence ◽  
Ion Concentration ◽  
Bimolecular Reactions ◽  
Hydrocarbon Flames ◽  
Ion Probe ◽  
Increased Sensitivity ◽  
N Compounds

The addition of 0.3% of the fuel-nitrogen (fuel-N) compounds HCN, NH3, or NO to a premixed, fuel-rich, CH4–O2–Ar flame burning at atmospheric pressure demonstrated the rapid interconversion of nitrogenous intermediates in the reaction zone. The nitrogenous species (HCN/CN, HNCO/NCO, NH3, NH2, NH, NO, NO2) were observed as ions (CN−, H2CN+, NCO−, H2NCO+, NH4+, NH3+, NH2+, NO+, NO2−, and hydrate ions) formed in chemical ionization processes discussed previously (1). The ions were sampled directly into a flame-ion mass spectrometer which had sufficient spatial resolution for the measurement of ion concentration profiles through the reaction zone. The study bears on Fenimore's suggestion for the formation of "prompt NO" in fuel-rich hydrocarbon flames. These additive results were compared with previous results involving nitrogenous species present in a similar CH4–O2 flame doped with 10% N2. The increased sensitivity of the additive approach confirmed many of the mass assignments and mechanisms involved in the N2 study. Reasonably good evidence was obtained for the elusive intermediate HNCO (and possibly isomeric HCNO as well) in protonated form, and also formamide, NH2CHO, which had not been detected previously. Similarities in profile peak positions and magnitudes observed for many ions, irrespective of the nature of the fuel-N additive, indicated that the nitrogenous species were linked by a network of fast bimolecular reactions, many of which appeared to be balanced in the reaction zone.

Ion chemistry of second-row transition metals in hydrocarbon flames: cations and anions of Y, Zr, Nb, and Mo

1995 ◽  
Vol 73 (12) ◽  
pp. 2263-2271 ◽  
Author(s):  
Christine C.Y. Chow ◽  
John M. Goodings
Keyword(s):  
Transition Metals ◽  
Gas Phase ◽  
Atmospheric Pressure ◽  
Chemical Ionization ◽  
Negative Ions ◽  
Ion Concentration ◽  
Oxidation States ◽  
Metallic Ions ◽  
Ion Chemistry ◽  
Hydrocarbon Flames

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.

Sulphurous negative ions in a fuel-rich, CH4–O2 flame with OCS additive

1983 ◽  
Vol 61 (8) ◽  
pp. 1703-1711 ◽  
Author(s):  
John M. Goodings ◽  
Kamal Elguindi ◽  
Diethard K. Bohme
Keyword(s):  
Reaction Zone ◽  
Atmospheric Pressure ◽  
Negative Ions ◽  
Ion Concentration ◽  
Quadrupole Mass ◽  
Ion Chemistry ◽  
Naturally Occurring ◽  
Pressure Profiles ◽  
Ion Profiles ◽  
Carbonyl Sulphide

Sulphurous negative ions S • SH • SO • SO2/S2• SO3• HSO3• SO4• and HSO4 were observed when 0.2% of carbonyl sulphide (OCS) was added to a conical, laminar, premixed. fuel-rich (equivalence ratio [Formula: see text]) CH4–O2 flame burning at atmospheric pressure. Profiles were obtained of ion concentration vs. distance along the flame axis by sampling the flame through a pinhole into a quadrupole mass spectrometer. Some of the ion signals observed in the flame reaction zone are very large, particularly that for HSO4. None of the sulphurous ions detected contain carbon. Of those listed above, only S−,•SH, • SO • and SO2 persist downstream through the burnt gas. The sulphurous ions are formed by chemical ionization processes of neutral sulphurous intermediates reacting with the naturally-occurring ions present in any hydrocarbon flame. The ion chemistry is discussed, as is the underlying neutral chemistry of sulphur relevant to the flame environment. The ion profiles show the rapidity with which OCS is oxidized through SH and SO to SO2 even within the reaction zone of this fuel-rich flame. No evidence was obtained for the presence of sulphuric or sulphurous acids, and the presence of S2: was not confirmed.

Sulphur anion chemistry in hydrocarbon flames with H2S, OCS, and SO2 additives

1986 ◽  
Vol 64 (4) ◽  
pp. 689-694 ◽  
Author(s):  
John M. Goodings ◽  
Diethard K. Bohme ◽  
Kamal Elguindi ◽  
Arnold Fox
Keyword(s):  
Rate Constants ◽  
Atmospheric Pressure ◽  
Room Temperature ◽  
Negative Ions ◽  
Ion Concentration ◽  
Concentration Profiles ◽  
Hydrocarbon Flame ◽  
Flowing Afterglow ◽  
Hydrocarbon Flames ◽  
Oxygen Flame

A premixed, fuel-rich, methane–oxygen flame at atmospheric pressure was doped separately with 0.2 mol% of H2S, OCS, and SO2 to probe the behaviour of fuel sulphur during combustion. These three additives represent compounds occurring early, intermediate, and late in the oxidation sequence of fuel sulphur. They are chemically ionized in the reaction zone of a hydrocarbon flame to give large signals of sulphurous negative ions. Those detected include S−, SH−, SO− (uncertain), SO2− (S2−), SO3−, HSO3−, CH3O−•SO2, SO4− (S2O2−, S3−), and HSO4−. Ion concentration profiles of these ions were measured along the conical flame axis by sampling the flame into a mass spectrometer. The shapes of the profiles are insensitive to the nature of the additive, but their relative magnitudes are indicative of the additive's position in the sulphur oxidation sequence. For each additive, the very large HSO4− signal has analytical implications as an indicator for total fuel sulphur. The sulphurous anion chemistry is discussed for each additive in terms of roughly twenty ion (electron)-molecule reactions of six basic types, whose rate constants were known previously, or were measured at room temperature using the York flowing afterglow apparatus.

Sulphur cation chemistry in a fuel-rich, CH4–O2 flame with OCS additive

1986 ◽  
Vol 64 (9) ◽  
pp. 1733-1742 ◽  
Author(s):  
Nicholas S. Karellas ◽  
John M. Goodings
Keyword(s):  
Reaction Zone ◽  
Atmospheric Pressure ◽  
Mass Spectra ◽  
Mass Range ◽  
Major Product ◽  
Premixed Flame ◽  
Ion Concentration ◽  
Concentration Profiles ◽  
Ion Chemistry ◽  
Ion Molecule Reactions

A fuel-rich, methane–oxygen, premixed flame at atmospheric pressure was doped with 0.2 mol% of OCS. More than 40 different sulphurous cations were observed in the mass range < 100 u by sampling the flame into a flame-ion mass spectrometer. Ion concentration profiles along the flame axis are presented, together with mass spectra at fixed points in the flame. In the reaction zone, primary sulphur ions CHxS+ (x = 1, 3, 5) undergo extensive ion–molecule reactions (association and condensation) with CH4/CH3, C2H2, and OCS to form a considerable variety of secondary sulphurous cations. Just downstream of the reaction zone, the ion chemistry is somewhat different; it appears to be dominated by reactions of primary sulphur ions including HxS+ (x = 0–3) with C2H2 present as an intermediate. A few ions (HxS+, OS+, S2+) persist throughout the burnt gas region in equilibrium with the natural flame ions CHO+ and H3O+. These sulphurous cation signals show the evolution of the sulphur chemistry, both ionic and neutral, through the flame reaction zone into the burnt gas downstream where H2S, not SO2, is the major product in fuel-rich combustion.

Ventilatory response to fixed acid evaluated by ‘iso-Pco2’ technique

1959 ◽  
Vol 14 (4) ◽  
pp. 557-561 ◽  
Author(s):  
Dario B. Domizi ◽  
John F. Perkins ◽  
Joan S. Byrne
Keyword(s):  
Carbon Dioxide ◽  
Ventilatory Response ◽  
Carbon Dioxide Tension ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Control Value ◽  
Anesthetized Dogs ◽  
Increased Sensitivity ◽  
Small Increments ◽  
Fixed Acid

In order to avoid changes in a second stimulus to ventilation, i.e. carbon dioxide, while measuring the response to fixed acid, a technique was utilized whereby alveolar carbon dioxide tension (PaCOCO2) could be held constant. This technique includes continuous recording of PaCOCO2 with an infrared type analyzer and addition of sufficient CO2 to the inspired air to keep PaCOCO2 at its control value (near 40 mm Hg). The response of anesthetized dogs to infusion of 0.5 m HCl was measured when the PaCOCO2 was held at the control value and also at various other levels. Other experiments measured the effect of CO2 when it was not allowed to change arterial hydrogen ion concentration [H+]. It was found that both these substances are potent respiratory stimuli and that their effects may be considered essentially separate and additive, as suggested by Gray. The experiments also demonstrated a slightly increased sensitivity to CO2 at increased arterial [H+], but this effect was not found necessary to explain the response to acid. Responses to successive small increments in PaCOCO2 failed to reveal any ‘threshold,’ even with CO2 tensions as low as 15 mm during acidosis. Submitted on December 29, 1958

Comparative sulphur cation chemistry in a hydrocarbon flame with H2S, OCS, and SO2 additives

1986 ◽  
Vol 64 (12) ◽  
pp. 2412-2417 ◽  
Author(s):  
Nicholas S. Karellas ◽  
John M. Goodings
Keyword(s):  
Reaction Zone ◽  
Atmospheric Pressure ◽  
Mass Spectra ◽  
Chemical Ionization ◽  
Negative Ions ◽  
Mass Range ◽  
Total Ionization ◽  
Ion Recombination ◽  
Diffusion Mass ◽  
Oxygen Flame

A fuel-rich, conical, premixed, methane–oxygen flame at atmospheric pressure was doped separately with 0.2 mol% of H2S, OCS, and SO2 to probe the chemistry of sulphur at its source during combustion. These three additives represent a broad range of fuel-sulphur contaminants since they occur early, intermediate, and late in the sulphur oxidation sequence. A wide variety of sulphurous cations, formed by chemical ionization reactions, is observed for each additive by sampling the flame into a mass spectrometer. The total ionization profile measured along the flame axis is enhanced in the reaction zone when a sulphur additive is present; the mechanism involves the formation of sulphurous negative ions which reduces the rates of cation loss by electron–ion recombination and ambipolar diffusion. Mass spectra measured in the mass range 10–110 u at fixed points on the flame axis are very similar for all three additives, and are not helpful in the identification of the additive. However, the general presence of sulphur is evident from large signals measured near the reaction zone at five principal mass numbers; namely, 45 u (CHS+), 47 u (CH3S+), 58 u (C2H2S+), 59 u (C2H3S+), and 69 u (C3HS+) related to CS, thioformaldehyde, thioketene, and C3S.

The chemical structure of premixed fuel-rich methane flames: the effect of hydrocarbon species in the secondary reaction zone

1991 ◽  
Vol 433 (1887) ◽  
pp. 1-21 ◽  
Keyword(s):  
Reaction Zone ◽  
Chemical Structure ◽  
Reaction Rates ◽  
Secondary Reaction ◽  
Partial Equilibrium ◽  
Oh Radicals ◽  
Primary Reaction ◽  
Bimolecular Reactions ◽  
Atom Concentration ◽  
Secondary Reaction Zone

In a previous paper the analysis of a fuel-rich, ф =1.60, methane flame using a four-stage molecular beam inlet to a quadrupole mass spectrometer was described. The results were used to investigate the chemical structure of the primary reaction zone of the flame. In this paper, results from a richer flame, ф = 2.00, are presented and analysed. This premixed, laminar, flat flame had the following composition (all molar percentages) and conditions: 35.0% (CH 4 ), 35.0% (O 2 ), 30% (Ar); pressure = 8.00 kPa; cold-gas velocity at 293 K = 0.47 m s -1 . Mole fraction profiles through each flame were measured for a large number of stable and radical species, and those for the ф = 2.00 flame are presented in this paper and are compared with the results from the ф = 1.60 flame published earlier. Analysis and discussion in the present paper concentrates on the secondary reaction zone of both fuel-rich flames. Comparison of the profiles shows that hydrocarbon species survive the primary reaction zone in increasing concentrations as ф increases. It is shown that the reaction H + O 2 ⇌ OH + O (21, -21 ) does not achieve the partial equilibrium condition that is found in leaner flames, although the remaining bimolecular reactions of the H 2 -O 2 system do so. The competition between various species for the H, O and OH radicals is analysed using a convenient parameter which allows comparison of reaction rates and which has been called the 'characteristic reaction time’, r . It is concluded that the direct cause of the inability of (21, -21) to achieve partial equilibrium is the removal of O atoms from the available pool of H, O and OH radicals by reaction with hydrocarbon species, particularly C 2 H 2 . The rate of decrease of the H atom concentration in the secondary reaction zone is shown to be too fast to be the result of termolecular recombination reactions; it is suggested that the cause is the rapid response of the fast bimolecular reactions of the H 2 -O 2 system to the removal of O atoms via OH + H → O + H 2 , (-22) OH + OH → O + H 2 O (-23) thus reducing the concentrations of H and OH radicals. This mechanism explains the reduction in the excesses of the H, O and OH radicals above their thermodynamic equilibrium levels that is observed with increasing ф . It is concluded that it is possible to view a rich flame as consisting entirely of an extended primary reaction zone in which the concentrations of the H, O and OH radicals are controlled by bimolecular reactions throughout.

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