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

Numerical Simulations of Turbulent Mixing and Autoignition of Hydrogen Fuel at Reheat Combustor Operating Conditions

[+] Author and Article Information
Elizaveta M. Ivanova1

 Institute of Combustion Technology, German Aerospace Centre (DLR), Stuttgart, 70569 Germanyelizaveta.ivanova@dlr.de

Berthold E. Noll

 Institute of Combustion Technology, German Aerospace Centre (DLR), Stuttgart, 70569 Germanyberthold.noll@dlr.de

Peter Griebel

 Institute of Combustion Technology, German Aerospace Centre (DLR), Stuttgart, 70569 Germanypeter.griebel@dlr.de

Manfred Aigner

 Institute of Combustion Technology, German Aerospace Centre (DLR), Stuttgart, 70569 Germanymanfred.aigner@dlr.de

Khawar Syed

Group Manager Combustor Technology  ALSTOM Power, Brown Boveri Strasse 7, 5400 Baden, Switzerlandkhawar.syed@power.alstom.com

GT24® and GT26® are registered trademarks of ALSTOM Technology Ltd.

1

Corresponding author.

J. Eng. Gas Turbines Power 134(4), 041504 (Jan 30, 2012) (7 pages) doi:10.1115/1.4004725 History: Received May 13, 2011; Revised May 19, 2011; Published January 30, 2012; Online January 30, 2012

Turbulent mixing and autoignition of H2-rich fuels at relevant reheat combustor operating conditions are investigated in the present numerical study. The flow configuration under consideration is a fuel jet perpendicularly injected into a crossflow of hot flue gas (T>1000K,p=15 bar). Based on the results of the experimental study for the same flow configuration and operating conditions, two different fuel blends are chosen for the numerical simulations. The first fuel blend is a H2/natural gas/N2 mixture at which no autoignition events were observed in the experiments. The second fuel blend is a H2/N2 mixture at which autoignition in the mixing section occurred. First, the non-reacting flow simulations are performed for the H2/natural gas/N2 mixture in order to compare the accuracy of different turbulence modeling methods. Here, the steady-state Reynolds- averaged Navier- Stokes (RANS) as well as the unsteady scale-adaptive simulation (SAS) turbulence modeling methods are applied. The velocity fields obtained in both simulations are directly validated against experimental data. The SAS method shows better agreement with the experimental results. In the second part of the present work, the autoignition of the H2/N2 mixture is numerically studied using the 9-species 21-steps reaction mechanism of O’Conaire (Int. J. Chem. Kinet., 36 (11), 2004). As in the reference experiments, autoignition can be observed in the simulations. Influences of the turbulence modeling as well as of the hot flue gas temperature are investigated. The onset and the propagation of the ignition kernels are studied based on the SAS modeling results. The obtained numerical results are discussed and compared with data from experimental autoignition studies.

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Figures

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Figure 10

Distribution of flow temperature T non-dimensionalized by the crossflow inlet temperature Tcf. Tcf is 60 K lower than in the basic case, t = 2 ms. The isolines of YOH=0.0001 are shown to indicate the flame front position.

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Figure 4

Distribution of the (time-averaged) y-component of the velocity vector Uy non-dimensionalized by the mean crossflow velocity Ucf. Horizontal white lines in the plots of the simulation results mark the edges of the optical access window of experiments [4]. (a) Experiment [4]. (b) RANS (c) SAS.

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Figure 3

Distribution of the (time-averaged) x-component of the velocity vector Ux non-dimensionalized by the mean crossflow velocity Ucf. Horizontal white lines in the plots of the simulation results mark the edges of the optical access in the experiments [4]. (a) Experiment [4]. (b) RANS (c) SAS.

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Figure 2

Computational grid for the sas simulations. Cross-sections in different positions along the mixing zone of the main channel.

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Figure 1

Computational domain

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Figure 9

Distribution of flow temperature T non-dimensionalized by the crossflow inlet temperature Tcf. The isolines of YOH = 0.0001 are shown to indicate the flame front position. (a) t = 0 ms (b) t = 0.1 ms (c) t = 0.3 ms (d) t = 1 ms (e) t = 2 ms.

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Figure 8

Distribution of the YOH contours. The isolines of Ux=0 are shown to indicate the recirculation zone position. (a) t = 0 ms (b) t = 0.1 ms (c) t = 0.3 ms (d) t = 1 ms (e) t = 2 ms.

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Figure 7

Distribution of the x-component of the velocity vector Ux non-dimensionalized by the mean crossflow velocity Ucf. The isolines of YOH=0.0001 are shown to indicate the flame front position. (a) t = 0 ms (b) t = 0.1 ms (c) t = 0.3 ms (d) t = 1 ms (e) t = 2 ms.

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Figure 6

Stable flame isosurfaces of YOH  = 0.0001 (a) RANS (b) SAS.

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Figure 5

Isosurfaces of YOH=0.0001 at different time points of the SAS simulation (a) t = 0 ms (b) t = 0.1 ms (c) t = 0.3 ms (d) t = 1 ms (e) t = 2 ms.

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