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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

# Large-Eddy Simulation of a Reacting Jet in Cross Flow With NOx Prediction

[+] Author and Article Information
Johannes Weinzierl

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: weinzierl@td.mw.tum.de

Michael Kolb, Denise Ahrens, Christoph Hirsch, Thomas Sattelmayer

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 23, 2016; final manuscript received June 27, 2016; published online September 27, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 031502 (Sep 27, 2016) (7 pages) Paper No: GTP-16-1273; doi: 10.1115/1.4034447 History: Received June 23, 2016; Revised June 27, 2016

## Abstract

The reduction of full and part load emissions and the increase of the turndown ratio are important goals for gas turbine combustor development. Combustion techniques, which generate lower $NOx$ emissions than unstaged premixed combustion in the full load range, and which have the potential of reducing minimum load while complying with emission legislation, are of high technical interest. Therefore, axial-staged combustion systems have been designed, either with or without expansion in a turbine stage between both stages. In its simpler form without intermediate expansion stage, a flow of hot combustion products is generated in the first stage of the premixed combustor, which interacts with the jets of premixed gas injected into the second stage. The level of $NOx$ formation during combustion of the premixed jets in the hot cross flow determines the advantage of axially staged combustion regarding full load $NOx$ emission reduction. Employing large-eddy simulation in openfoam, a tool has been developed, which allows to investigate staged combustion systems including not only temperature distribution but also $NOx$ emissions under engine conditions. To be able to compute $NOx$ formation correctly, the combustion process has to be captured with sufficient level of accuracy. This is achieved by the partially stirred reactor model. It is combined with a newly developed $NOx$ model, which is a combination of a tabulation technique for the $NOx$ source term based on mixture fraction and progress variable and a partial equilibrium approach. The $NOx$ model is successfully validated with generic burner stabilized flame data and with measurements from a large-scale reacting jet in cross flow experiment. The new $NOx$ model is finally used to compute a reacting jet in cross flow under engine conditions to investigate the $NOx$ formation of staged combustion in detail. The comparison between the atmospheric and the pressurized configuration gives valuable insight in the $NOx$ formation process. It can be shown that the $NOx$ formation within a reacting jet in cross flow configuration is reduced and not only diluted.

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## Figures

Fig. 3

Comparison of NOx production of a flat flame using detailed chemistry or the coupling of tabulation with partial equilibrium

Fig. 2

Overview of the contribution of the four NOx pathways depending on the total NOx production for a methane flame at Φ=0.66, a fresh gas temperature of 636 K, and a pressure of 20 bar. The second y-axis shows the progress variable. The time is set to zero at a temperature of 1000 K.

Fig. 1

Overview of the contribution of the four NOx pathways depending on the total NOx production for a methane flame at Φ=0.66, a fresh gas temperature of 636 K, and a pressure of 1 bar. The second y-axis shows the progress variable. The time is set to zero at a temperature of 1000 K.

Fig. 4

Outline of the simulation domain. All the dimensions are given in relation to the jet diameter D.

Fig. 5

Mean temperatures are displayed at x/D=8 on the left from atmospheric simulation and on the right from experiment

Fig. 6

NOx concentration of simulation of atmospheric configuration (left) and experiment (right) is displayed in ppm and normalized to 15%

Fig. 7

Mean temperature and residence time of atmospheric configuration at a plane normal to the x-direction at x/D=8

Fig. 8

Mean (left) and instantaneous (right) reaction rates ω˙NO on the symmetry plane of atmospheric configuration

Fig. 9

Mean (left) and instantaneous (right) NOx mass fraction on the symmetry plane for atmospheric configuration

Fig. 10

Mean (left) and instantaneous (right) NOx distribution at x/D=4 for pressurized conditions

Fig. 11

Mean (left) and instantaneous (right) reaction rates ω˙NO at y/D=0 for pressurized conditions

Fig. 12

Mean (left) and instantaneous (right) temperature from pressurized configuration at y/D=0. In black, an isocontour representing 1/10 of the maximum heat release rate.

Fig. 13

Mean (left) and instantaneous (right) NOx mass fraction at y/D=0 for pressurized conditions

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