Numerical Investigation of the Pressure Effect on the NOx Formation in a Lean-Premixed Gas Turbine Combustor

In this work, the influence of pressure on NOx formation in a lean-premixed gas turbine combustor is investigated at both atmospheric (1 atm) and elevated (15 atm) pressures. A network of chemical reactors was developed based on the flow, temperature, and species fields obtained using CFD to model the combustion process. Detailed chemical kinetics were developed with a combination of GRI Mech 3.0 and the lately proposed nitrogen chemistry. A premixed combustor was developed for a full-scale atmospheric combustion test. The model predictions with the proposed mechanism were validated with the experimental data at atmospheric pressure. The combustion in the gas turbine combustor was simulated at 1 and 15 atm and equivalence ratios of 0.45, 0.5, and 0.55. The present study focuses on the effects of pressure on NOx emissions by analyzing the NO formation pathways. In the zone of the main flame, prompt and NNH NO formations are relatively similar to thermal and N2O NO formations; however, thermal and N2O NO formations are dominant in the recirculation and the post flame zone. The predicted NOx emission at the elevated pressure (15 atm) increases at the equivalence ratio 0.55 showing the positive pressure exponential dependency, but at the equivalence ratio of 0.45, it shows the negative pressure exponent dependency. At the equivalence ratio F = 0.5 the predicted NOx emissions were similar showing the weak negative pressure dependency. The path analysis was conducted to understand the effect of pressure.