This paper describes the investigation on the characteristics of a two-stage lean premix combustion technique for gas turbine combustors. Numerical as well as experimental methods have been applied to gain detailed understanding of the combustion phenomena. Emphasis has been put on the oxidation behavior of CH_4 and CO in the secondary stage in which the primary hot combustion product mixes with the secondary ultra lean premixture. The computer code CHEMKIN has been used to numerically analyze the chemical kinetics of combustion. The effects of process parameters on the oxidation of CH_4 and CO have been identified. A test combustor has been used to examine the results of the numerical analysis and to gain further understanding of the combustion phenomena in a practical combustor. It has been demonstrated that temperature is the most important parameter for the oxidation of CH_4 and CO. When the temperature in the secondary stage is maintained higher than approximately 900-1000 deg C, the secondary ultra lean premixture can be successfully oxidized for a wide range of operating conditions, in particular for that of the secondary excess air ratio, even though it is out of the flammability limit. By using the knowledge gained by this study, ultra low NO_x emission (10 ppm 0percent O_2 at 1 ata) and high combustion efficiency have been successfully accomplished.
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