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

Ignition Probability in a Stratified Turbulent Flow With a Sunken Fire Igniter

[+] Author and Article Information
Brandon Sforzo

Ben T. Zinn Combustion Laboratory,
Guggenheim School of Aerospace Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0150,
e-mail: brandon.sforzo@gatech.edu

Jaecheol Kim, Jeff Jagoda, Jerry Seitzman

Ben T. Zinn Combustion Laboratory,
Guggenheim School of Aerospace Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0150

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 8, 2014; final manuscript received July 13, 2014; published online August 26, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(1), 011502 (Aug 26, 2014) (8 pages) Paper No: GTP-14-1331; doi: 10.1115/1.4028208 History: Received July 08, 2014; Revised July 13, 2014

The evolution of a spark kernel ejected by a sunken fire igniter into a turbulent, fuel–air stratified crossflow was studied both experimentally and using a model in a configuration that is similar to the conditions found in turbine engine combustors. This study allows for variations in the transit time of the kernel across a uniform nonflammable region, before entering a second stream containing a flammable fuel–air mixture. High speed schlieren and emission imaging systems are used to visualize the evolution of the kernel and determine the probability of ignition based on measurements over many spark events. Experiments are performed for a range of mean velocities, transit times, inlet (preheat) temperatures, flammable zone equivalence ratios, and nonflammable zone equivalence ratios. In addition to the typical dependence of ignition on the equivalence ratio of the flammable mixture, the results indicate the strong influence of the kernel transit time and the inlet flow temperature on the probability of ignition. The entrainment between the kernel and the surrounding flow appears to be primarily controlled by the kernel ejection-induced flowfield. Reduced-order modeling suggests that the lowering of the kernel temperature associated with entrainment of the nonflammable mixture significantly reduces the ignition probability, and leads to the conclusion that the presence of fuel close to the igniter is necessary to ensure reliable ignition under adverse conditions.

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Fig. 1

Annular combustor with (30) igniter mounted through the (26) outer casing and (14) outer liner [15]

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Fig. 2

Superposition of approximately ten kernel trajectories from a high-speed movie in a 25 m/s crossflow. The igniter is located at (0,0) and flow is left to right. Color bar indicates the number of times a kernel edge is observed at a given location.

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Fig. 3

Schematic of the stratified flow facility

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Fig. 4

Schematic of data acquisition system layout (HSC: high speed camera)

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Fig. 5

Two-stage reactor model for ignition kernel evolution including mass entrainment through nonflammable and flammable mixture zones

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Fig. 6

Time progression of a kernel ejected from igniter. Schlieren visualization depicts kernel reaching splitter boundary (overlaid white line) at 60 μs ± 10 μs.

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Fig. 7

Example long-exposure emission image showing developing flame kernel, edges highlighted; failed ignition attempts show no emission (flow is from right to left)

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Fig. 8

Parameters sorted by t-ratio representing their influence in the model. The vertical lines depict the 0.05 significance level (α).

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Fig. 9

Ignition probabilities at several splitter plate heights for varying equivalence ratios and 300 K inflow temperature

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Fig. 10

Probability of ignition at increased inlet temperatures, taken at two splitter plate heights

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Fig. 11

Temperature history for cases from Table 3

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Fig. 12

Selected species (CH4 and OH) time history for cases from Table 3




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