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Research Papers

Flame and Spray Dynamics During the Light-Round Process in an Annular System Equipped With Multiple Swirl Spray Injectors

[+] Author and Article Information
Kevin Prieur

Laboratoire EM2C,
CNRS,
CentraleSupélec,
Université Paris-Saclay,
3, rue Joliot Curie,
Gif-sur-Yvette cedex 91192, France;
Safran Tech,
E&P,
Châteaufort,
CS 80112,
Magny-Les-Hameaux 78772, France

Guillaume Vignat

Laboratoire EM2C,
CNRS,
CentraleSupélec,
Université Paris-Saclay,
3, rue Joliot Curie,
Gif-sur-Yvette cedex 91192, France,
e-mail: guillaume.vignat@centralesupelec.fr

Daniel Durox, Sébastien Candel

Laboratoire EM2C,
CNRS,
CentraleSupélec,
Université Paris-Saclay,
3, rue Joliot Curie,
Gif-sur-Yvette cedex 91192, France

Thierry Schuller

Institut de Mécanique des Fluides de Toulouse,
IMFT,
Université de Toulouse, CNRS,
Toulouse, France

1Corresponding author.

Manuscript received November 4, 2018; final manuscript received November 10, 2018; published online January 9, 2019. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(6), 061007 (Jan 09, 2019) (11 pages) Paper No: GTP-18-1671; doi: 10.1115/1.4042024 History: Received November 04, 2018; Revised November 10, 2018

A successful ignition in an annular multi-injector combustor follows a sequence of steps. The first injector is ignited; two arch-shaped flame branches nearly perpendicular to the combustor backplane form; they propagate, igniting each injection unit; they merge. In this paper, characterization of the propagation phase is performed in an annular combustor with spray flames fed with liquid n-hepane. The velocity and the direction of the arch-like flame branch are investigated. Near the backplane, the flame is moving in a purely azimuthal direction. Higher up in the chamber, it is also moving in the axial direction due to the volumetric expansion of the burnt gases. Time-resolved particle image velocimetry (PIV) measurements are used to investigate the evaporating fuel droplets dynamics. A new result is that, during the light-round, the incoming flame front pushes the fuel droplets in the azimuthal direction well before its leading point. This leads to a decrease in the local droplet concentration and local mixture composition over not yet lit injectors. For the first time, the behavior of an individual injector ignited by the passing flame front is examined. The swirling flame structure formed by each injection unit evolves in time. From the ignition of an individual injector to the stabilization of its flame in its final shape, approximately 50 ms elapse. After the passage of the traveling flame, the newly ignited flame flashbacks into the injector during a few milliseconds, for example, 5 ms for the conditions that are tested. This could be detrimental to the service life of the unit. Then, the flame exits from the injection unit, and its external branch detaches under the action of cooled burnt gases in the outer recirculation zone (ORZ).

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References

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Lancien, T. , Prieur, K. , Durox, D. , Candel, S. , and Vicquelin, R. , 2017, “ Large Eddy Simulation of Light-Round in an Annular Combustor With Liquid Spray Injection and Comparison With Experiments,” ASME J. Eng. Gas Turbines Power, 140(2), p. 021504. [CrossRef]
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Figures

Grahic Jump Location
Fig. 1

Left: photograph of the MICCA-spray annular combustor with sixteen liquid spray injectors. A detailed schematics of the injector is available on the bottom left of the image. Middle: schematic view of the chamber backplane showing the locations of the camera and of different microphones MCx (chamber microphone n°x) in the chamber and MPx (plenum microphone n°x) in the air plenum. The spark plug location is indicated and defines flame 1. A steel plate is added in the center to block the luminosity of the opposite flame branch. The aim of the camera is either one injector or between two injectors, depending on the experiment. Right: view of the position of the camera in black with a cut of two sectors of the annular combustor. The gray-dashed lines symbolize the field of view of the camera.

Grahic Jump Location
Fig. 2

Passage of the traveling flame at four different instants during the light-round. The camera is placed on the side of the combustor and its optical axis is at the level of the chamber backplane. The luminosity of the other flame branch propagating in the other half of the annular combustor is blocked by a steel plate placed in the central plane of the system. The origin of time t =0 ms corresponds to the ignition of a hot kernel by the spark plug. In the bottom image, one can see three different ignited injectors, while one other injector is being swept by the traveling flame front.

Grahic Jump Location
Fig. 3

Result of a PIV processing of the flame passage at two different instants during the light-round. Regions I and II correspond to different flame propagation behaviors and are explained in the text. The origin of time t =0 ms corresponds to the ignition of a hot kernel by the spark plug. Velocity vectors are colored by their magnitude using the colormap inserted below the images. See online figure for color.

Grahic Jump Location
Fig. 4

Top: Images of the flame propagation with a laser slice to visualize the motion of the droplet spray. Camera position is given in Fig. 1. Bottom: Velocity fields calculated using PIV on the n-heptane droplets. False vectors have been eliminated. The time origin t =0 ms corresponds to the ignition of a hot kernel by the spark plug. Velocity vectors are colored by their magnitude using the colormap inserted on the right of the images. See online figure for color.

Grahic Jump Location
Fig. 5

Four ignition sequences showing the evolution of the time-averaged flame shape after the passage of the flame front. The time origin t =0 ms corresponds to the instant when the injector is ignited by the incoming flame front.

Grahic Jump Location
Fig. 6

Left: flame shape 5 ms after the flame front ignites this injector (top, shape A) and Abel transform of the flame (bottom, shape A). Right: flame shape 88 ms after the flame front ignites this injector (top, shape B) and Abel transform of the flame (bottom, shape B). Images are represented in false colors and saturated to highlight their different structures. Yellow and white correspond to high light intensities, while dark red represents low light emission levels. The Abel transform gives rise to errors in the near vicinity of the axis so that the values in this region should not be considered. See online figure for color.

Grahic Jump Location
Fig. 7

Mean images of three consecutive flames of the annular combustor progressively switching from shape A to shape B. In the first image, the flame front propagates from right to left. The first flame to be ignited is flame α.

Grahic Jump Location
Fig. 8

Acoustic pressure recorded by four pressure sensors in the plenum (first and third graphs) and by eight pressure sensors in the chamber (second and fourth graphs) before and after the light-round. Note that the third and fourth figures are expanded views of the pressure tracks in the plenum and in the chamber during ignition. In the bottom graph, the black lines correspond to successive pressure peaks, each associated with the ignition of an injector. For clarity, the signals are low-passed filtered with a cutoff frequency of 500 Hz.

Grahic Jump Location
Fig. 9

Schematic representation of the SICCA-spray burner with key dimensions

Grahic Jump Location
Fig. 10

Top: True-color ignition sequences in SICCA-spray. Bottom: Close-up images at t =5 and 21 ms. Extra white luminosity is due to the sparks used to ignite the system, which are continuously operated at 100 Hz. See online figure for color.

Grahic Jump Location
Fig. 11

Top: Velocity u and flame luminosity I signals during ignition of the single SICCA-spray injector. The black-dotted line corresponds to the mean velocity at nominal operating conditions. The red dotted line is a linear regression of the measured air velocity. Bottom: The signals are processed using a Butterworth low pass filter at 200 Hz, underlining the sudden decrease of the flowrate and its readjustment after the flame passage. See online figure for color.

Grahic Jump Location
Fig. 12

Pressure loss measurements in the SICCA-spray burner as a function of the velocity at the hot-wire probe position. The values are fitted with the model of Eq. (3). The value at the nominal operating conditions is indicated by a red dot.

Grahic Jump Location
Fig. 13

Velocity obtained at the hot wire position using model M1 (blue, Eq. (2)) and M2 (red, Eq. (4)). The velocity measured by the hot wire is shown as a thin black line. The pressure perturbation used for the present calculation is shown as a thicker black line on top, associated with the right axis. See online figure for color.

Grahic Jump Location
Fig. 14

Top: True-color low-speed images of the light-round in the MICCA combustion chamber under premixed propane-air conditions with ϕ = 0.76 and P=60 kW. Bottom: Three ignition sequences of the SICCA burner equipped with the premixed swirled injector with ϕ = 0.76 and P=3.75 kW.

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