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Research Papers: Gas Turbines: Heat Transfer

A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

[+] Author and Article Information
Michael Kolb

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

Denise Ahrens, Christoph Hirsch, Thomas Sattelmayer

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

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received December 5, 2015; final manuscript received December 11, 2015; published online March 1, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(8), 081901 (Mar 01, 2016) (9 pages) Paper No: GTP-15-1560; doi: 10.1115/1.4032421 History: Received December 05, 2015; Revised December 11, 2015

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multistage combustion to lower nitric oxide emissions and enhance turn-down ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large-scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off (LO) behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet LO depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K), and jet momentum ratio (6–210). The differences to existing LO studies are the high cross flow temperature and applying a premixed jet. The LO height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the LO height for similar staged combustion systems. A main outcome of this work is that the LO height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz-number. Furthermore, the ignition delay time scale τign also misses part of the LO height mechanism. The presented model uses turbulent time scales, the ignition delay, and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

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References

Figures

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Fig. 1

Scheme of jet in cross flow experiment

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Fig. 8

Sensitivity of LO to changes of the jet and cross flow temperature as well as the equivalence ratio of the jet: ϕj=0.66−0.82, TX = 1643–1821 K, Tj = 288–673 K, and J = 210

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Fig. 7

Influence of jet equivalence ratio on LO for different momentum ratios: ϕj=0.59−0.82, TX = 1643 K, Tj = 288 K, amd J = 6–210

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Fig. 6

Influence of cross flow temperature on LO for different momentum ratios: ϕj=0.82, TX = 1643–1821 K, Tj = 288 K, and J = 6–210

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Fig. 5

Influence of jet temperature on LO for different momentum ratios: ϕj=0.82, TX = 1643 K, Tj = 288–673 K, and J = 6–210

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Fig. 4

Influence of jet velocity on LO for different momentum ratios: ϕj=0.66, TX=1643 K, Tj=288 K, J=6−210, uj=13−82 m/s,andDj=0.015−0.1 m

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Fig. 3

Image series of the flame chemiluminescence. An auto-ignition event at the flame base can be observed.

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Fig. 2

Method to measure the LO height from the OH* chemiluminescence images

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Fig. 17

LO of all operation points over a Karlovitz mixture and ignition delay Damköhler number with mixture fraction f = 0.6 assumed

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Fig. 9

Laminar flame speed for different jet preheat temperatures over a preflame mixture of jet and cross flow using the correlation for methane from Ref. [20]. One corresponds to jet material and zero to cross flow material only: ϕj=0.82, TX = 1643 K, and Tj = 288–673 K.

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Fig. 10

Calculated laminar flame speeds of different preflame mixtures and measured inverse flame surface area over ϕ: ϕj=0.59−0.82, TX = 1643 K, and Tj = 288 K

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Fig. 11

LO over a Karlovitz number using only the jet composition for ϕj=0.82, TX = 1643 K, Tj = 288–673 K, and J = 6–210

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Fig. 12

LO over a Karlovitz mixture number of a jet cross flow mixture for ϕj=0.82, Tx = 1643 K, Tj = 288–673 K, and J = 6–210

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Fig. 13

LO over a Karlovitz mixture number for different crossflow temperatures Tx = 1643–1832 K: ϕj=0.66−0.82, Tj = 288–673 K, and J = 6–210

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Fig. 14

LO over a ignition delay Damköhler number using constant equivalence ratio ϕj=0.82 and jet temperature Tj = 288 K with momentum ratio range J = 6–210

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Fig. 15

LO over a ignition delay Damköhler number for ϕj=0.66−0.82 and Tj = 288–673 K with momentum ratio range J = 6–210

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Fig. 16

LO of all operation points over a Karlovitz mixture and ignition delay Damköhler number

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