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

Autoignition Limits of Hydrogen at Relevant Reheat Combustor Operating Conditions

[+] Author and Article Information
J. Fleck

 German Aerospace Center (DLR), Institute of Combustion Technology, Pfaffenwaldring 38-40, 70569 Stuttgart, GermanyJulia.Fleck@DLR.de

P. Griebel, A.M. Steinberg, M. Stöhr, M. Aigner

 German Aerospace Center (DLR), Institute of Combustion Technology, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

A. Ciani

 ALSTOM Power Ltd., Brown-Boveri-Strasse 7, 5400 Baden, Switzerland

ALSTOM® is a registered trademark; GT24® , GT26® are registered trademarks of ALSTOM Technology Ltd.

J. Eng. Gas Turbines Power 134(4), 041502 (Jan 25, 2012) (8 pages) doi:10.1115/1.4004500 History: Received April 27, 2011; Revised May 27, 2011; Published January 25, 2012; Online January 25, 2012

The use of highly reactive fuels in the lean premixed combustion systems employed in stationary gas turbines can lead to many practical problems, such as unwanted autoignition in regions not designed for combustion. In the present study, autoignition characteristics for hydrogen, diluted with up to 30 vol. % nitrogen, were investigated at conditions relevant to reheat combustor operation (p = 15 bar, T >1000 K, hot flue gas, relevant residence times). The experiments were performed in a generic, optically accessible reheat combustor, by applying high-speed imaging and particle image velocimetry. Autoignition limits for different mixing section (temperature, velocity) and fuel jet (N2 dilution) parameters are described. The dominant factor influencing autoignition was the temperature, with an increase of around 2% leading to a reduction of the highest possible H2 concentration without “flame-stabilizing autoignition kernels” of approximately 16 vol. %. Furthermore, the onset and propagation of the ignition kernels were elucidated using the high-speed measurements. It was found that the ability of individual autoignition kernels to develop into stable flames depends on the initial position of the kernel and the corresponding axial velocity at that position. While unwanted autoignition occurred prior to reaching the desired operating point for most investigated conditions, for certain conditions the reheat combustor could be operated stably with up to 80 vol. % H2 in the fuel.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Reheat combustor

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Figure 2

Example of a chronological sequence of the H2 mass flow rate, temperature and pressure in the mixing section at ignition (black line). The data are logged every second.

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Figure 3

H2 concentration in the fuel in vol. % versus temperature TMS in mixing section at flame-stabilizing autoignition, normalized by the nominal baseline temperature TBL-H2

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Figure 4

H2 concentration in the fuel in vol. % versus uMS at flame-stabilizing autoignition for TBL-H2 , normalized by the nominal baseline velocity uBL-H2

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Figure 5

Single shot high-speed images (side and top view) extracted from two cases, one flame-stabilizing (a) and one non-stabilizing (b) ignition event (test case B2 and E2, respectively). Red lines indicate leading edge of the initial ignition kernel occurrence.

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Figure 6

Typical plots for the positions of the first ignition kernel occurrence derived from the side and top-view high-speed images. Top line: A; bottom line: D2. Open markers: non-stabilizing kernels, closed markers: flame-stabilizing kernels.

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Figure 7

Axial mean and axial rms velocities measured at the z = 0 mm and z = −7 mm planes for H2 /NG/N2  = 74/4/22 vol. % (J = 1.5) and H2 /NG/N2  = 62/8/30 vol. % (J = 3.5), normalized by uBL-H2 . Black lines: axial position of the fuel injector, red lines: region in which the flame-stabilizing ignition kernels occurred, blue lines: downstream of these lines the non-stabilizing kernels were located.

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