This numerical study investigates the flame characteristics of premixed methane with various dilutions in order to simulate oxy-combustion of hydrocarbon fuels with flue gas recirculation system. In general, a recirculated flue gas consists of high concentration CO2/H2O and high gas temperature. The effect of various diluent gases on laminar burning velocity and adiabatic flame temperature is discussed via using Chemkin-pro simulation. By observing the resultant flame temperature and species concentration profiles one can identify that the flame front shifts, and the concentration profiles of major chemical reaction radicals varies, indicating the change of flame structure and flame chemical reaction paths. The dominant initial consumption reaction step of methane shifts from R53 (H + CH4CH3 + H2) to R98 (OH + CH4CH3 + H2O) when nitrogen is replaced by the recirculated gases. H and OH radical concentration would be influenced in various diluent gas cases, so that it leads to affect hydrogen formation and methane consumption. It is because that the chemical effects of the recirculated gases change the chemical reaction of the oxy-fuel combustion, and further affect reaction rate, species and radical concentrations.
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