Detailed analysis of low-pressure premixed flames of CH4 + O2 + N2: a study of prompt-NO

Abstract A detailed experimental study of low-pressure premixed CH 4 /O 2 /N 2 flames has been undertaken for equivalence ratios of 0.8–1.2, to provide an experimental data base for testing chemical mechanisms of hydrocarbon combustion and their ability to predict NO formation. The experimental procedure involved microprobe sampling and gas chromatographic analysis (GC), together with laser-induced fluorescence (LIF). The major and intermediate stable species were determined using GC. Concentrations of OH, CH, and NO were measured by one-photon LIF; those of CO, H, and O by a two-photon excitation scheme. All concentrations, except that of CH, were measured absolutely using an appropriate calibration method. Temperature was measured using the LIF excitation technique on the OH radical. Predictions from three chemical kinetic models, based on the Miller and Bowman (MB) and Gas Research Institute (GRI) mechanisms, are compared with the experimental results. In the case of major and reactive species, the experimental results are well reproduced by the modeling. However some discrepancies are observed for the C 2 hydrocarbon intermediates. The measured concentrations of CH and NO vary with equivalence ratio as predicted by the MBGRI 1.2 mechanism (the MB scheme for forming NO has been added to the GRI 1.2 one for the oxidation of CH 4 ). Under our experimental conditions the kinetic analysis shows a preponderance of prompt-NO formation. Trends in the evolution of CH with equivalence ratio are well predicted by the GRI 2.11 mechanism, but important disagreements are pointed out for predictions of NO. Important discrepancies are also observed in the amounts of CH and NO with the MB mechanism. These discrepancies are developed and could be directly linked to uncertainties in the reactions of CH and H 2 .

[1]  Robert W. Dibble,et al.  Experimental and numerical comparison of extractive and in situ laser measurements of non-equilibrium carbon monoxide in lean-premixed natural gas combustion , 1995 .

[2]  C. Carter,et al.  Laser-Saturated Fluorescence Measurements of Nitric Oxide in Laminar, Flat, C2H6/O2/N2 Flames at Atmospheric Pressure , 1993 .

[3]  J. Jeffries,et al.  LIF measurements in methane/air flames of radicals important in prompt-NO formation , 1992 .

[4]  J. W. Fleming,et al.  Kinetic study of the reaction CH(X 2Π)+H2⇄CH2(X 3B1)+H in the temperature range 372 to 675 K , 1986 .

[5]  James A. Miller,et al.  Mechanism and modeling of nitrogen chemistry in combustion , 1989 .

[6]  Peter Glarborg,et al.  Kinetic modeling and sensitivity analysis of nitrogen oxide formation in well-stirred reactors , 1986 .

[7]  R. Borghi,et al.  Further Results on Nitrogen Oxides Production in Combustion Zones , 1981 .

[8]  J. W. Fleming,et al.  Comparison of species profiles between O2 and NO2 oxidizers in premixed methane flames , 1995 .

[9]  R. Cattolica.  OH radical nonequilibrium in methaneair flat flames , 1982 .

[10]  A. Dean,et al.  Laser induced fluorescence and absorption measurements of NO in NH3/O2 and CH4/air flames , 1983 .

[11]  J. Goldsmith,et al.  Photochemical effects in 205-nm, two-photon-excited fluorescence detection of atomic hydrogen in flames. , 1986, Optics letters.

[12]  Robert S. Barlow,et al.  Raman/Rayleigh/LIF measurements of nitric oxide formation in turbulent hydrogen jet flames , 1994 .

[13]  N. Laurendeau,et al.  Laser-Induced Fluorescence Measurements and Modeling of Nitric Oxide Formation in High-Pressure Flames , 1994 .

[14]  J. W. Fleming,et al.  Comparative species concentrations in CH4/O2/Ar flames doped with N2O, NO, and NO2 , 1994 .

[15]  Gregory P Smith,et al.  Pressure and temperature dependence of the reactions of CH with N2 , 1996 .

[16]  N. Laurendeau,et al.  Quantitative LIF measurements and modeling of nitric oxide in high-pressure C2H4/O2/N2 flames , 1995 .

[17]  Michael C. Drake,et al.  Calculations of NOx Formation Pathways in Propagating Laminar, High Pressure Premixed CH4/Air Flames , 1991 .

[18]  Y. Matsui,et al.  Spectroscopic study of prompt nitrogen oxide formation mechanism in hydrocarbon-air flames , 1978 .

[19]  R. Hanson,et al.  Quantitative two-photon LIF imaging of carbon monoxide in combustion gases. , 1987, Applied optics.

[20]  U. Meier,et al.  Quenching of two-photon-excited H(3s, 3d) and O(3p 3P2,1,0) atoms by rare gases and small molecules , 1988 .

[21]  J. Goldsmith,et al.  Photochemical effects in two-photon-excited fluorescence detection of atomic oxygen in flames. , 1987, Applied optics.

[22]  P. Desgroux,et al.  Improvement of two-photon laser induced fluorescence measurements of H- and O-atoms in premixed methane/air flames , 1997 .