Flue gas recirculation(FGR) induces the change of combustion temperature

oxygen volume fraction and residence time

thus to affect the NO formation during the combustion process. By using the perfectly-stirred reactor computations with detailed chemical kinetics

this paper numerically studies the effect of FGR on NO formation during CH4 combustion. The FGR induced temperature and oxygen concentration reduction and residence time variation were particularly considered. The results showed that

10 % of the FGR rate resulted in a significant NO reduction by 40%～60%

while the NO suppression effect of FGR became limited when the FGR ratio exceeded 30%. The NO formation pathways differed at varied excess air ratios. The FGR induced temperature reduction dominated the overall NO reduction

while the reduced oxygen concentration played a minor role. The NO formation during the CH_4 combustion could be effectively inhibited if FGR was adopted with proper residence time control.