Kinetic Modeling Study on the Emission Characteristics of an Axial-Fuel-Staged Model MILD Combustor

Abstract

Axial-fuel-staged combustion is a promising technology that can be applied to lower emission, higher combustor outlet temperature, and extended operational flexibility of gas turbines. In this paper, two simplified chemical reactors network (CRN) models based on the staged combustion were established to investigate the emission characteristics of an axial-fuel-staged MILD (moderate or intense low-oxygen dilution) combustor. Firstly, an atmospheric experiment of a staged MILD combustor was performed to validate the CRN model. Results show that the experimental NOx emission trend is well captured by this CRN model and a NOx reduction of approximately 30% was also achieved by the staged combustion. Subsequently, based on the validated CRN model, a parametric study was conducted and the effects of fuel distribution, residence time, mixing characteristics in the secondary stage and heat losses were systematically analysed. The results show that the NOx emission can be reduced by more than 40% with an unaffected combustion efficiency by both increasing the ratio of secondary fuel and decreasing the ratio of secondary residence time. On the other hand, poor mixing in the secondary stage will significantly increase the thermal NO formation by 140% due to the local high temperature region. Finally, a non-adiabatic CRN model was studied and it was found that the heat loss would exaggerate the NOx-abatement potential of the axial-fuel-staged MILD combustor.