Kinetic analysis of the addition of CO_2 to the flame in the combustion of methane

摘要

The paper presents the results of the calculation of the effect of the CO_2 addition in the combustion of methane in air enriched in oxygen up to 25 vol% on the variations in the concentrations of free radicals, CO and NO. The calculations constitute a complement to performed experiments with injecting CO_2 at varying distances from the burner. Modelling of the kinetics of methane combustion was done in the Chemked II program by implementing the reaction mechanism GRI-Mech, version 3.0. Residence times of the reagents at temperatures of 1200, 1500 and 1800 K, necessary for obtaining the peak concentrations of H, OH, O and CO, have been determined. It has been demonstrated that the addition of CO_2 reduces the peak concentrations of H, OH and O the stronger, the higher the temperature is. If the temperature in the flame region is at a level of 1200 K, then the CO_2 addition lengthens the time necessary for achieving the peak reagent concentrations. For T=1100 K, a negligible effect of adding CO_2 on the variation in the mole fractions of H, OH, O, CO was noted. The paper enumerates the predominant reactions included in the employed GRI-Mech system, which determine the consumption and production of H, OH, O, CO and NO in the flame.