The influence of carbon monoxide and hydrogen on the structure and extinction of nonpremixed and premixed methane flames

An experimental and computational study is carried to elucidate the influence of carbon monoxide (CO) addition to nonpremixed methane (CH4) flames. A Burke-Schumann (flame-sheet) formulation is applied to laminar counterflow diffusion-flame experiments, reported here, in which CO was added to either methane-nitrogen mixtures or oxygen-nitrogen mixtures at normal atmospheric pressure, with both feed streams at normal room temperature. Experimental conditions were adjusted to fix selected values of the stoichiometric mixture fraction and the adiabatic flame temperature, and the strain rate was increased gradually until extinction occurred. At the selected sets of values, the strain rate at extinction was measured as a function of the CO concentration in the fuel or oxidizer stream. It was found that with increasing amounts of CO in the oxidizer stream, the strain rate at extinction first increased and then decreased. With increasing amounts of CO in the fuel stream, changes in values of the strain rate at extinction was small in comparison to those measured for CO addition to the oxidizer stream. The experimental results are in agreement with predictions obtained employing detailed chemistry. A numerical investigation was carried out to characterize the influence of hydrogen and carbon monoxide on the structure and burning velocities of stoichiometric premixed methane flames. The mass fraction of the reactants in the mixture were so chosen that the adiabatic temperature is constant. The flame speed increases when hydrogen is added to the reactant stream. For CO addition the flame speed first increases and then decreases.