Experimental Study on the Emissions Characteristics of a Premixed Axial-Fuel-Staged Model Combustor

Axial-fuel-staged combustion is a promising technology to reduce NO_x emission at high turbine inlet temperatures and provide extended gas turbine operational flexibility. To investigate the emissions characteristics of the axial-fuel-staged combustion, a staged model combustor was constructed and a parametric study was performed at atmospheric pressure. Fuel distribution, equivalence ratio, and jet velocity effects on the emissions characteristics have been studied in the present research. Results show that the influence of fuel distribution on emissions is depending on the combustor outlet temperature. The NO_x emissions increase with secondary fuel fraction when the combustor outlet temperature is low but decrease when the combustor outlet temperature is high. Investigation of the equivalence ratio on each stage shows that a lower relative NO_x increase in secondary combustion zone is achieved at higher first-stage equivalence ratio. Moreover, the secondary stage jet velocity was varied to study the jet mixing influence on the emissions. The results show that a higher jet velocity will enhance the mixing between the secondary jet and the upstream first-stage burnt gases, producing lower NO_x emissions. Finally, a simplified axial-fuel-staged combustion chemical reactors network (CRN) model was established to study the mixing of the secondary fresh fuel/air mixture and the first-stage burnt gases. The CRN modeling results show that a poor mixing in the secondary stage will significantly increase the NO_x emission, which means that the mixing enhancement at the secondary stage is important for the axial-fuel-staged combustor design.