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

Numerical Investigation of the Parameter Governing the Ignitability of a Spray Flame

[+] Author and Article Information
J. M. Boyde

e-mail: jan.boyde@dlr.de

M. Aigner

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

1Address all correspondence to this author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 23, 2012; final manuscript received August 1, 2012; published online November 30, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(1), 011506 (Nov 30, 2012) (9 pages) Paper No: GTP-12-1296; doi: 10.1115/1.4007377 History: Received July 23, 2012; Revised August 01, 2012

This paper contains a numerical examination concerning the ignition behavior of a spray nozzle mounted in a rectangular channel under atmospheric conditions, which is run with Jet A-1. On the basis of a comprehensive data set of experimental results, the numerical approach is verified primarily by means of a comparison of the flame growth and position after ignition. In the following, several distinct igniter positions and boundary condition settings are simulated. The conditions that prevail at the location of the ignition are investigated with respect to how they influence the ignition process. Due to changes in the fuel placement and flow field characteristics, which follow from alternating the boundary conditions, such as air and fuel mass flow, ignition is either promoted or impeded. The underlying causes that can lead to a success or failure of the ignition are analyzed. The ignition in the experiment is achieved through a laser-induced breakdown, which is modeled through a turbulent flame speed closure combustion model with an additional spark ignition extension. A comparison with the ignition statistics from the experiment shows that numerical tools can be used to determine preferential boundary conditions and igniter locations to accomplish a successful ignition in multiphase flow configurations.

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Fig. 1

Sketch of the domain. Air enters from the top. The fuel droplets emerge from the spray injector in the upper half of the channel. The measurement area is located underneath the injector exit plane.

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Fig. 2

Dimensions of the numerical domain

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Fig. 3

Left: comparison of measured velocities (left half) and simulated velocities (right half) for the single phase flow of 40 m3/h. Right: droplet velocities in the experiment and simulation for 40 m3/h and 15 SLM. (Note that, in the simulation, insufficient droplet parcels have passed for the 10 mm plane for r > 3 mm to obtain meaningful values.)

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Fig. 4

Investigated ignition locations. The cross-axis displacement is kept constant at z = −4 mm. For the axis location, four distinct distances to the nozzle exit plane are chosen: x = 1 cm, 2 cm, 3 cm, 4 cm.

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Fig. 5

Left: maximum temperature for the ignition occurring at 1 cm downstream location for three different nozzle air flows. Right: maximum temperature for a fixed nozzle air flow with the ignition location varied between 1-cm, 2-cm, 3-cm, and 4-cm downstream position.

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Fig. 6

Experimentally derived ignition probability for all investigated conditions and igniter positions

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Fig. 7

Maximum and mean fuel vapor mass fractions (of the entire domain) for the ignition taking place at 1 cm for the 10 SLM (successful) and 15 SLM (unsuccessful) setting and at 2 cm for the 15 SLM (successful) setting. Circles represent the ignition for 10 SLM at 1-cm position. Triangles correspond to the ignition for 15 SLM at 1-cm position. Diamonds relate to the ignition for 15 SLM at 2-cm position. Solid lines are the maximum values. Dotted lines represent the mean value × 103.

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Fig. 8

Gas flow velocities at 1-cm distance from the injector plane. Larger spray cone angle for the 10 SLM case leads to an increased velocity in the ignition region.

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Fig. 10

Left: averaged values of T and Yfuel for the 3 cm and 4 cm ignition normalized with the averaged values of the initial conditions before ignition. The value for T is multiplied by 3 to emphasize the differences. Right: maximum values of T and Yfuel for the 3-cm and 4-cm ignition normalized with the maximum value occurred.

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Fig. 11

Cross correlation of temperature and fuel mass fraction. The plot corresponds to the expression y = max(T-300,0.0)·YC10H22 within the investigated volume, as specified. The values are normalized with the maximum value.

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Fig. 9

Gas and droplet velocities at 3 cm and 4 cm downstream of the nozzle exit plane. The droplets are grouped in classes (C1=∧d < 15 μm, C2 =∧ d < 40 μm).




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