Flame characteristics and NO emission in methane/air-air counterflow premixed flames with applying FIR and FGR

Numerical study was conducted to grasp flame characteristics and NO emission behaviors in CH4/air-air premixed counterflow flames with applying Fuel induced recirculation (FIR) and Flue gas recirculation (FGR) with CO2 and H2O by varying global strain rate and the ratios of FIR and FGR. Chemical effects of additional CO2 and H2O via FIR and FGR were analyzed through comparing flame characteristics and NO behaviors from real species (CO2 and H2O) with those from their artificial species (XCO2 and XH2O) which have the same thermochemical, radiative, and transport properties to those for the real species. The results showed that flame temperature and NO emission with FIR varied much more sensitively than that with FGR. Those varied little via FIR with CO2 and H2O as well as XCO2 and XH2O. However, those varied complicatedly by chemical effects of added CO2 and H2O via FGR. In particular, there is a critical ratio of FGR below which NO emission index can be larger than those without applying FGR. Detailed analyses for them were made and discussed.