Laminar flame speeds and extinction strain rates of mixtures of carbon monoxide with hydrogen, methane, and air

Abstract

The effect of hydrogen and methane addition on the propagation and extinction of atmospheric CO/airflames was investigated experimentally and numerically. Experiments were conducted by using the counterflow, twin-flame technique and laser-Doppler velocimetry for the determination of laminar flame speeds and extinction strain rates. The simulation was conducted by using the one-dimensional flame code, and by solving the conservation equations of mass, momentum, energy, and species along the stagnation stream-line of the counterflow. In both cases, detailed description of the chemistry and transport was used. Results indicate that the addition of small amounts of hydrogen and methane to CO flames increases the laminar flame speeds and extinction strain rates by accelerating the main CO oxidation reaction. The sensitivity of the mass burning rate to this reaction is particularly high when trace amounts of hydrogen and methane are added. For large amounts of additives, the chemistry shifts toward that of the additive, and the advantages of the CO kinetic simplicity are lost. The experimental data were closely predicted by the numerical calculations for both propagation and extinction, indicating that existing CO, hydrogen, and methane kinetics can be used with confidence for similar studies. Detailed analysis of the flame structure revealed that, when CO and methane are both supplied as reactants, the CO oxidation follows that of methane, and that, for methane-rich mixtures, the supplied CO remains unreacted until the intermediate CO has been completely formed.