Comparative study of the influence of СО$_2$ and Н$_2$О on the chemical structure of lean and rich methane-air flames at atmospheric pressure

A comparative study of the influence of СО$_2$ and Н$_2$О on both lean and rich CH$_4$-air laminar flames is performed. Six premixed flames are stabilized on a flat flame burner at atmospheric pressure: lean (with the equivalence ratio maintained constant at $\phi$ = 0.7) and rich (with the equivalence ratio maintained constant at $\phi$ = 1.4) CH$_4$-air, CH$_4$-CO$_2$-air, and CH$_4$-H$_2$O-air flames. These flames are studied experimentally and numerically. The [CO$_2$]/[CH$_4$] and [H$_2$O]/[CH$_4$] ratios are kept equal to 0.4 for both flames series. Species mole fraction profiles are measured by gas chromatography and Fourier transform infrared spectroscopy analyses of gas samples withdrawn along the vertical axis by a quartz microprobe. Flames structures are computed by using the ChemkinII/Premix code. Four detailed combustion mechanisms are used to calculate the laminar flame velocities and species mole fraction profiles: GRI-Mech 3.0, Dagaut, UCSD, and GDFkin®3.0.