A reactor model for the NOx formation in a reacting jet in hot cross flow under atmospheric and high pressure conditions

Staged combustion is a promising technology for gas turbines to achieve load flexibility and low NOx emission levels at the same time. Therefore, a large scale atmospheric test rig has been set up at the Institute of Thermodynamics, Technical University of Munich to study NOx emission characteristics of a reacting jet in hot cross flow. The premixed primary combustion stage is operated at Φ = 0.5 and provides the hot cross flow. In the second stage a premixed jet at Φ = 0.77 is injected perpendicular to the first stage. In both stages natural gas is used as fuel and air as oxidant. This paper presents a reactor model approach for the computation of the resulting NOx concentrations. The mixing and ignition process along the jet streamline of maximum NOx formation is simulated using a perfectly stirred reactor with Cantera 1.8. The reactor model is validated for the ambient pressure case using experimental data. Afterwards, a high pressure simulation is performed in order to investigate the NOx emission characteristics under gas turbine conditions. The NOx formation is divided into flame NOx and post flame NOx. The reactor model reveals that the formation of post flame NOx in the second combustion stage can be efficiently suppressed due to fast mixing with cross flow material and the corresponding temperature reduction. Compared to single stage combustion with the same power output, no NOx reduction was observed in the experiment. However, the results from the reactor model suggest a NOx reduction potential at gas turbine conditions caused by the increased influence of post flame NOx production at high p ressure.