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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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