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Title: Diode laser absorption measurement and analysis of HCN in atmospheric-pressure, fuel-rich premixed methane/air flames

Abstract

Measurements of HCN in flat, fuel-rich premixed methane/air flames at atmospheric pressure are reported. Quartz-microprobe sampling followed by wavelength modulation absorption spectroscopy with second harmonic detection was used to obtain an overall measurement uncertainty of better than 20% for mole fractions HCN on the order of 10 ppm. The equivalence ratio, {phi}, was varied between 1.3 and 1.5, while the flame temperature was varied independently by changing the mass flux through the burner surface at constant equivalence ratio. Under the conditions of the experiments, the peak mole fractions vary little, in the range of 10-15 ppm. Increasing the flame temperature by increasing the mass flux had little influence on the peak mole fraction, but accelerated HCN burnout substantially. At high equivalence ratio and low flame temperature, HCN burnout is very slow: at {phi}=1.5, {proportional_to}10ppm HCN is still present 7 mm above the burner surface. Substantial quantitative disagreement is observed between the experimental profiles and those obtained from calculations using GRI-Mech 3.0, with the calculations generally overpredicting the results significantly. Changing the rates of key formation and consumption reactions for HCN can improve the agreement, but only by making unreasonable changes in these rates. Inclusion of reactions describing NCN formation andmore » consumption in the calculations improves the agreement with the measurements considerably. (author)« less

Authors:
;  [1];  [1];  [2]
  1. Laboratory for Fuel and Combustion Science, University of Groningen (Netherlands)
  2. (Netherlands)
Publication Date:
OSTI Identifier:
21116110
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 155; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; HYDROCYANIC ACID; NITRIC OXIDE; METHANE; LAMINAR FLAMES; AIR; ATMOSPHERIC PRESSURE; COMBUSTION PROPERTIES; TEMPERATURE DEPENDENCE; BURNERS; BURNOUT; MASS; MATHEMATICAL MODELS; ACCURACY; NITROGEN COMPOUNDS; CYANIDES; Diode laser absorption spectroscopy

Citation Formats

Gersen, S., Mokhov, A.V., Levinsky, H.B., and Gasunie Engineering and Technology, N.V. Nederlandse Gasunie, Groningen. Diode laser absorption measurement and analysis of HCN in atmospheric-pressure, fuel-rich premixed methane/air flames. United States: N. p., 2008. Web. doi:10.1016/J.COMBUSTFLAME.2008.04.006.
Gersen, S., Mokhov, A.V., Levinsky, H.B., & Gasunie Engineering and Technology, N.V. Nederlandse Gasunie, Groningen. Diode laser absorption measurement and analysis of HCN in atmospheric-pressure, fuel-rich premixed methane/air flames. United States. doi:10.1016/J.COMBUSTFLAME.2008.04.006.
Gersen, S., Mokhov, A.V., Levinsky, H.B., and Gasunie Engineering and Technology, N.V. Nederlandse Gasunie, Groningen. Wed . "Diode laser absorption measurement and analysis of HCN in atmospheric-pressure, fuel-rich premixed methane/air flames". United States. doi:10.1016/J.COMBUSTFLAME.2008.04.006.
@article{osti_21116110,
title = {Diode laser absorption measurement and analysis of HCN in atmospheric-pressure, fuel-rich premixed methane/air flames},
author = {Gersen, S. and Mokhov, A.V. and Levinsky, H.B. and Gasunie Engineering and Technology, N.V. Nederlandse Gasunie, Groningen},
abstractNote = {Measurements of HCN in flat, fuel-rich premixed methane/air flames at atmospheric pressure are reported. Quartz-microprobe sampling followed by wavelength modulation absorption spectroscopy with second harmonic detection was used to obtain an overall measurement uncertainty of better than 20% for mole fractions HCN on the order of 10 ppm. The equivalence ratio, {phi}, was varied between 1.3 and 1.5, while the flame temperature was varied independently by changing the mass flux through the burner surface at constant equivalence ratio. Under the conditions of the experiments, the peak mole fractions vary little, in the range of 10-15 ppm. Increasing the flame temperature by increasing the mass flux had little influence on the peak mole fraction, but accelerated HCN burnout substantially. At high equivalence ratio and low flame temperature, HCN burnout is very slow: at {phi}=1.5, {proportional_to}10ppm HCN is still present 7 mm above the burner surface. Substantial quantitative disagreement is observed between the experimental profiles and those obtained from calculations using GRI-Mech 3.0, with the calculations generally overpredicting the results significantly. Changing the rates of key formation and consumption reactions for HCN can improve the agreement, but only by making unreasonable changes in these rates. Inclusion of reactions describing NCN formation and consumption in the calculations improves the agreement with the measurements considerably. (author)},
doi = {10.1016/J.COMBUSTFLAME.2008.04.006},
journal = {Combustion and Flame},
number = 1-2,
volume = 155,
place = {United States},
year = {Wed Oct 15 00:00:00 EDT 2008},
month = {Wed Oct 15 00:00:00 EDT 2008}
}
  • The profiles of C{sub 2}H{sub 2} mole fractions were measured in flat atmospheric-pressure rich-premixed methane/air flames using microprobe gas sampling followed by tunable diode laser absorption spectroscopy (TDLAS), and compared the results with predictions of one-dimensional flame calculations. Acetylene concentrations are also determined by spontaneous Raman scattering to quantify possible uncertainties due to chemical reactions on the probe surface or acceleration of the combustion products into the probe.
  • Effects of pressure on NO formation in CH{sub 4}/air flames at a fixed equivalence ratio of 1.3 are investigated. The axial profiles of temperature, OH, CH, and NO mole fractions are measured using laser-induced fluorescence and compared with one-dimensional flame calculations. The measured and calculated temperature, CH, and NO profiles in free flames are observed to vary upon increasing the pressure from 40 to 75 Torr, following a scaling law derived for a chemical mechanism containing only second-order reactions. At pressures 300-760 Torr, the measurements and calculations in burner-stabilized flames show increasing flame temperature and NO mole fractions when themore » mass flux is increased linearly with pressure, while the CH profiles remain unchanged. The observed deviation from the scaling law in the temperature profiles arises from the increasing contribution of three-body reactions to the flame front propagation velocity, leading to a decrease in the degree of burner stabilization. The deviation from the pressure scaling law for the NO mole fractions is due to the temperature dependence of the rate coefficient for the reaction between CH and N{sub 2} and the fact that the temperature profiles themselves do not scale. In contrast, the surprisingly good scaling of the CH mole fractions with pressure indicates the dominant role of two-body reactions participating in the chain of chemical reactions leading to CH formation. The calculations using GRI-Mech 3.0 substantially overpredict (up to 50%) the measured nitric oxide concentrations for all pressures studied. The observed differences in the NO mole fraction may be addressed by improving the CH prediction. (author)« less
  • No abstract prepared.
  • This work presents results from detailed chemical kinetics calculations of electronically excited OH (A{sup 2}{sigma}, denoted as OH{sup *}) and CH (A{sup 2}{delta}, denoted as CH{sup *}) chemiluminescent species in laminar premixed and non-premixed counterflow methane-air flames, at atmospheric pressure. Eight different detailed chemistry mechanisms, with added elementary reactions that account for the formation and destruction of the chemiluminescent species OH{sup *} and CH{sup *}, are studied. The effects of flow strain rate and equivalence ratio on the chemiluminescent intensities of OH{sup *}, CH{sup *} and their ratio are studied and the results are compared to chemiluminescent intensity ratio measurementsmore » from premixed laminar counterflow natural gas-air flames. This is done in order to numerically evaluate the measurement of equivalence ratio using OH{sup *} and CH{sup *} chemiluminescence, an experimental practise that is used in the literature. The calculations reproduced the experimental observation that there is no effect of strain rate on the chemiluminescent intensity ratio of OH{sup *} to CH{sup *}, and that the ratio is a monotonic function of equivalence ratio. In contrast, the strain rate was found to have an effect on both the OH{sup *} and CH{sup *} intensities, in agreement with experiment. The calculated OH{sup *}/CH{sup *} values showed that only five out of the eight mechanisms studied were within the same order of magnitude with the experimental data. A new mechanism, proposed in this work, gave results that agreed with experiment within 30%. It was found that the location of maximum emitted intensity from the excited species OH{sup *} and CH{sup *} was displaced by less than 65 and 115 {mu}m, respectively, away from the maximum of the heat release rate, in agreement with experiments, which is small relative to the spatial resolution of experimental methods applied to combustion applications, and, therefore, it is expected that intensity from the OH{sup *} and CH{sup *} excited radicals can be used to identify the location of the reaction zone. Calculations of the OH{sup *}/CH{sup *} intensity ratio for strained non-premixed counterflow methane-air flames showed that the intensity ratio takes different values from those for premixed flames, and therefore has the potential to be used as a criterion to distinguish between premixed and non-premixed reaction in turbulent flames. (author)« less
  • A detailed experimental investigation has been performed on the structures of five low-pressure CH{sub 4}/O{sub 2}/Ar flames at equivalence ratios of 0.92--1.94 (20--60 Torr). Stable compounds, atoms and radicals have been monitored using molecular beam mass spectrometry. The maximum mole fraction of CH{sub 3} radicals is roughly similar in all the flames investigated, whereas those of C{sub 2}H{sub 2}, C{sub 2}H{sub 4}, C{sub 3}H{sub 3}, C{sub 3}H{sub 4} and C{sub 4}H{sub 2} increase strongly with the equivalence ratio. For these species there is a dependence on the equivalence ratio ({Phi}). These results have been supported by a simple kinetic mechanismmore » involving these species. The exponent on {Phi} depends on the species considered and varies as follows: C{sub 4}H{sub 2} > C{sub 2}H{sub 2} >C{sub 3}H{sub 3} > C{sub 3}H{sub 4} > C{sub 2}H{sub 4}. This means that the peak mole fraction of C{sub 4}H{sub 2} increases faster than that of C{sub 3}H{sub 4} with the equivalence ratio. From the net reaction rate of C{sub 2}H{sub 4}, the rate coefficient has been determined for the reaction CH{sub 3} + CH{sub 3} {yields} C{sub 2}H{sub 6}, which is the main process leading to the first C{sub 2} compound. Moreover, it has been established that the formation of C{sub 3}H{sub 4} must proceed through the formation of the propenyl radical C{sub 3}H{sub 5} by reaction between C{sub 2}H{sub 2} and CH{sub 3}. The experimental rate coefficient of this reaction is 5.5 {+-} 2.5 {times} 10{sup 10} cm{sup 3}/mol s at 1,670 K. In addition, disappearance of C{sub 2}H{sub 2}, C{sub 3}H{sub 4} and C{sub 4}H{sub 2} by reaction with H atoms has been examined. The deduced rate coefficients at 1,650 K are 3 {+-} 1 {times} 10{sup 11}, 1.75 {+-} 0.5 {times} 10{sup 12}, 8.1 {+-} 3 {times} cm{sup 3}/mol s, respectively.« less