Basic Research for Reduction of NO_x Emission in Premixed combustion

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The structure of the premixed turbulent flame is divided into two categories, namely, wrinkled laminar flame and distributed reaction zone. Extremely strong turbulence is required to produce the distributed reaction zone, and our knowledge on the emission characteristics of this flame structure is insufficient. In the present study, a ceramic opposed jet burner was designed to assure the adiabaticity. NO_x concentration was measured by two chemiluminescence NO-NO_x analyzers and the stable chemical species were measured by the simultaneous multi-species analyzing system designed using 3 gas chromatographs. The burner has the bell-mouthed exits of propane/air mixture supply tube to eliminate the production of the recirculation zones around the exits. Purely one-dimensional concentration field was established due to the strong mixing perpendicular to the radially stretched vortex vector.In the distributed reaction zone, NO_x formed in the flame zone originates mainly from the prompt-NO mechanism rather than the Zeldovich mechanism and increased with the equivalence ratio. However, in the completely burned gas region, the NO_x formed through the Zeldovich mechanism is predominant and reaches a maximum at the stoichiometric concentration. The amount of NO_x emitted from this burner is extremely small and the emission index is of the order of 1g/kgfuel.By the simultaneous multi-species analyzing system, the concentrations of O_2, N_2, H_2, CO,CO_2, CH_4, C_2H_2, C_2H_4, C_2H_6, C_3H_6, C_3H_6, C_3H_8, i-C_4H_<10>, n-C_4H_<10> are able to be measured simultaneously. The sensitivity of the analyzing system was calibrated against the pure gases. The lower hydrocarbons which are formed by pyrolysis of propane on the unburned gas side of the flame zone are consumed rapidly on the unburned gas side. On the burned gas side, no such lower hydrocarbons were found and the chemical stucture is different from that on the unburned gas side.