Experimental study and kinetics modeling of partial oxidation reactions in heavily sooting laminar premixed methane flames

Abstract

The partial oxidation (POX) of methane in heavily sooting laminar premixed methane/oxygen flames was studied with an emphasis on acetylene formation and depletion. The flame temperature profiles were measured with a Pt/Pt–Rh thermocouple coated with Y2O3–BeO ceramic. Gas species along the flame axis were sampled by a quartz probe for their concentrations to be measured by a mass spectrometer. The problem of soot deposition on the sampling probe was overcome by in situ cleaning of the nozzle orifice. The mole ratios of O2/CH4 in the experiments were 0.55, 0.60, 0.65 and the STP (standard temperature and pressure) reactant flow velocity was fixed at 4cm/s. Computational results based on the Curran, Wang–Frenklach and GRI 3.0 detailed chemistry mechanisms were compared with the experimental results. The values predicted by the Curran and Wang-Frenklach mechanisms for the reaction conditions of this study were within the acceptable range. The maximum concentrations of acetylene were positioned in the flame area at 4–8mm distance from the burner, and were behind the positions of the maximum mole fractions of ethane and ethylene. Much more diacetylene and benzene were generated in the post-flame area than in the flame. Recombination reactions to larger hydrocarbon molecules and oxidation with hydroxyl radicals in the post-flame region were the main reactions responsible for acetylene depletion in the fuel rich methane flame.