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INTRODUCTION: Soot : a black, carbonaceous substance produced
during the incomplete combustion of organic substances such as
coal, wood, oil, etc.
Soot formation in turbulent flames:Turbulence and combustion are
intimately relatedA Complex process: involves complex interactions
among the turbulence, thermochemistry, diffusion,Nucleation,
oxidation and agglomeration processes.Important in combustion
devices such as :industrial furnaces, gas turbines , internal
combustion enginesUnavailability of an universal theory or model
that is applicable to different fuels and a wide range of flow
conditions OBJECTIVE:better understanding of soot formation process
in turbulent flames. Provide a new data base for modelling soot
formation in turbulent flamessince limited data base
Method: Stereoscopic Particle Image Velocimetry technique (SPIV)
coupled with Laser Induced Incandescence (LII).SPIV: measure the
instantaneous 3 velocity components whereas LII provides
instantaneous 2D soot distribution.
Figure: SPIV/LII Experimental optical set up
Figure : Burner SchematicThe BurnerFuel: mixture of pure
ethylene and pure methaneThe fuel jet is surrounded by co-annular
dry air flow of 400 mm in diameter in order to provide a
homogeneous and controlled co-flow oxidizer.
Four fuel mixtures of ethylene and methane have been used The
total flow rate is 10L/min.Fuel compositionEthylene (L/min)Methane
(L/min)100E-0M10075E-25M7.52.550E-50M5530E-70M37
100% E- 0 % M75% E- 25 % M50% E- 50 % M30% E- 70 % MThe higher
the ethylene mole fraction is, the brightest the flame is.Soot
Volume fraction increases with the ethylene proportion.
Post Processing of the LII Images:The first post-processing
consists of the subtraction of raw LII images by the background
flame luminosity as shown in the FigFigure : Post-processing of LII
image (100% ethylene, 100 mm HAB(a) The background flame luminosity
(max intensity about 1100 u.a),(b) The LII signal + the background
flame luminosity (max intensity about 11000 u.a), (c) resulting
image after post-processing (max intensity about 10000 u.a)
Figure 6: instantaneous PIV image with corresponding velocity
field of SCMOS camera 1(upper) and camera 2 (bottom) for 50 mm HAB
in the 50E-50M flame
Figure : Resulting instantaneous SPIV image at 50 mm HAB in the
50E-50M flame. (a) Vector length in y direction, (b) Magnitude of
the planar velocity SPIV vectors were obtained by stereo
reconstruction using Davis 8 software.
Figure: Instantaneous LII image recorded simultaneously with the
previous SPIV image at 50 mm HAB in the 50E-50M flame
Further Processing of the LII images: (Thresholding, Dilation
and Erosion, Labeling and Measuring Objects in the binary
Image)
Figure: u_meanFigure: v_meanFigure: w_mean
Figure: c_mean
Figure: cc Figure: cu Figure: cv Figure: cw Mean
ComponentsCorrelations
Turbulent StressesFigure: uuFigure: vvFigure: vwFigure:
wwFigure: uvFigure: uw
Figure: Instantaneous Velocity field with missing particles due
to vaporization of the seeding (olive oil) particlesFigure:
Instantaneous Velocity Field with interpolated missing data Figure:
Vorticity Field
Figure: Kinetic EnergyFigure: RMS of a series of 150 fields
CONCLUSION:SPIV technique has been combined with instantaneous
LII measurements in turbulent sooting flames. Statistical
investigation to determine the correlation between soot formation
areas and the turbulent flow in the different flames. Further works
will be focused on the simplification of the optical set-up in view
of industrial applications and on the acquisition of a detailed
database SPIV/LII in the new-designed burner.
ACKNOWLEDGEMENTS:The work is supported by the AFDAR project
(Advanced Flow Diagnostics for Aeronautical Research) funded by the
European Communitys Seventh Framework programme.
ECOLE CENTRALE DE LILLELABORATOIRE MECANIQUE DE LILLE
SUBJECT OF THE PRACTICE: PROCESSING OF COMBINED MEASUREMENTS OF
VELOCITY AND SOOT VOLUME FRACTION FIELDS IN A TURBULENT JET
FLAME
Prepared by: Suman Khanal Advisor: Prof. Michel
StanislasInternational Masters in Turbulence L.M.L. UMR CNRS
8107Ecole Centrale de Lille
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