NOx Formation in a Reacting Premixed Jet in Hot Cross Flow

Abstract

The NOx emissions of a premixed jet in hot cross flow configuration have been studied experimentally and with simple Cantera models. Staged combustion is realized by a first reaction zone providing a flow of fully combusted products and a secondary combustion stage downstream which consists of a premixed jet injected into the hot cross flow. The focus of the study lies on the overall NOx emission reduction potential of this generic configuration with respect to single stage premixed combustion employed in the high load regime of most large gas turbines for power generation. Cantera benchmark calculations were made to address that question. The second stage reaction was modeled using two different configurations: The worst case scenario being the combustion of the mixture in the jet without any interaction with the hot cross flow, and the most favorable case being the jet and the cross flows perfectly mixed and then burned. All calculations were performed under atmospheric and high pressure conditions to illustrate the influence of pressure on the potential of staging on the reduction of NOx emissions. In parallel to the modeling the NOx formation was studied in an atmospheric test rig. For that purpose emission and temperature data were collected with single orifice probe traverses four jet diameters downstream. The thermocouple probe was calibrated against CO-equilibrium concentration data from thermodynamic modeling. Furthermore, a planar laser diagnostic technique using Mie scattering was applied for determining the mixing of jet and cross flow. The mixture field was statistically analyzed to detect differences in spatial and temporal mixing. Finally all data were used to study NOx formation under atmospheric pressure and to transfer the results to gas turbine combustor conditions.