Experimental and Numerical Study on NOx Emissions Characteristics in a Coaxial Staged Combustor

Abstract A deep understanding of NOx formation characteristics and correlations can significantly enhance the operational adjustment efficiency of gas turbine combustors. To reduce pollutants emissions, this study proposed a coaxial staged combustion technology, experimental and numerical work was further conducted to investigate the impact of fuel stage ratio on NOx formation in an industrial gas turbine combustor operating at different loads. The dome equivalence ratio was ranging from 0.455 to 0.635, the fuel stage ratio was ranging from 0.27 to 3.23. Experimental results show that NOx emissions can be controlled within 25 ppm at 15% O2 with the combustor outlet temperature up to 1673 K. There exists an optimal fuel stage ratio that leads to the lowest NOx emissions. Moreover, as the dome equivalence ratio increases, the optimal fuel stage ratio decreases. Numerical results indicate that NOx generation through the prompt mechanism is negligible. At low-power conditions, NOx is primarily generated at the flame front through the N2O intermediate pathway. In contrast, at high-power conditions, NOx is mainly produced in the burnout and recirculation zones through the thermal pathway. Thermal NOx is highly sensitive to fuel stage ratios, unlike the relatively stable NOx production via the N2O intermediate mechanism. Based on the experimental data, it was found that the inner stage flame temperature has a more significant impact on NOx emissions. Furthermore, a new NOx emissions prediction model within an error of 20% that considers the impact of two-stage swirl flames was proposed.