Effects of N2 dilution on laminar burning velocity, combustion characteristics and NOx emissions of rich CH4-air premixed flames

Effects of N-2 dilution on laminar burning velocity (LBV), adiabatic flame temperature (AFT), intermediate radicals (CH3, H) and NOx emissions (NO, N2O) of methane were investigated using Bunsen burner under the condition of fuel-rich combustion (equivalence ratio 1.0 to 1.4). The Aramco mechanism was selected to analyze the effect of N-2 blending on the adiabatic flame temperature and the intermediate radicals of CH4 premixed flame under the equivalence ratios (Phi = 0.8, 1.0, 1.2). The effect of different N-2 doping ratios on the NOx emissions (NO, N2(O)) of methane was analyzed by using GRI 3.0 mechanism. The experimental and numerical results showed that as the equivalence ratio increased (from 1.0 to 1.4), the laminar burning velocity first increased and then decreased, reaching a maximum when the equivalence ratio was about 1.05. The mole fraction changes of intermediate radicals and NOx emissions also showed a trend of increasing first and then decreasing with the increasing of equivalence ratios. Under the same equivalence ratio, the mole fraction of intermediate radicals and NOx decreased as the N-2 doping ratio increased. The sensitivity analysis showed that the major elementary reactions that inhibits the generation of intermediate radicals and NOx emissions were different under different equivalence ratios and N-2 doping ratios. In addition, the sensitivity coefficients of the elementary reactions that mainly promotes or inhibits the generation of free radicals and NOx decreased with the increasing of the N-2 addition.