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Droplet temperature measurement by Laser Induced Fluorescence

Droplet temperature measurement by Laser Induced Fluorescence. by Guillaume Castanet *. Christophe Maqua. Fabrice Lemoine. * Guillaume.Castanet@ensem.inpl-nancy.fr. Context – Spray applications in combustion processes. Heat engines. Aeroengines. Industrial burners. Heat.

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Droplet temperature measurement by Laser Induced Fluorescence

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  1. Droplet temperature measurement by Laser Induced Fluorescence by Guillaume Castanet* Christophe Maqua Fabrice Lemoine *Guillaume.Castanet@ensem.inpl-nancy.fr

  2. Context– Spray applications in combustion processes Heat engines Aeroengines Industrial burners Heat Local air/fuel ratio Pollutants (NOx. HAP. CO. Soots.…) Atomization Unburnt products Optimization of the combustion efficiency Aims Reduction of pollution

  3. Combustion of monodisperse droplet streams Monodisperse stream Laminar flame time Heated coil (combustion igniter) Separation of parameters • -Diameter • -Interdroplet distance • -Velocity • -Temperature Membrane Rayleigh instability Steady phenomenon Water circulation for thermal regulation Piezoceramic Fuel inlet

  4. I- Measurement Technique

  5. Two-color laser induced fluorescence • Fluorescence intensity Liquid + fluorescent tracer Laser intensity Measurementvolume Induced fluorescence Optical constant Tracer concentration Dependence on temperature Laser excitation Neglected absorption (short optical path in a droplet) • Ratio of the fluorescence intensity on 2 bands Measurementvolume = Vdroplet Laser beam Vcollection

  6. 1st band 525-535 nm) 2nd band (>570 nm) 2300 1800 1300 800 300 -200 Selection of the spectral bands of detection Laser line (514,5 nm) T=25°C 1 0.9 Temperature sensitivity b(l) T=36°C 0.8 0.7 b (K-1) 0.6 T=57°C Intensity (A.U.) 0.5 0.4 0.3 0.2 0.1 0 510 530 550 570 590 610 630 650 670 l (nm) Emission spectrum of rhodamine B dissolved in ethanol Fluorescence emission law in liquids:

  7. Experimental Setup Interference filter [525 nm ; 535 nm] Dichroic beam splitter Fluorescence + Scattered light PMT 1 Notch filter Interference filter [>570 nm] Laser beams PMT 2 l=514.5 nm Analog filters with selectable frequency Channel 2 PDA Amplificators Channel 1 velocity + diameter Acquisition board

  8. II- Modeling of the aerothermal droplet-to-droplet interactions

  9. Combustion of ethanoldropletstreams C=9.1 C=11.5 D Injection flame L C=6,6 Heated coil igniting the combustion C=14.1 C=16.7 C=18.4 Electrodes for the electrostatic deviation of the drops

  10. Velocity and size measurements V/V0 Diameter Velocity (D/D0)2 D0 about 85 µm t (ms) t (ms) C=5 V=7,2 ms C=6,6 V=6,3 ms C=8,2 V=5,8 ms C=9,8 V=5,6 ms C=14,6 V=5 ms

  11. Volume averaged temperature measurements Heating phase Equilibrium phase Teq»60°C <Tboiling t (ms) - Limited influence of C - More noticeable influences of D and V

  12. Overall energy balance (radiation neglected) FC :Convective heat flux between the droplet and the gaseous phase Fvap :Evaporation flux QL: Internal heat flux entering into the droplet Sherwood number : Nusselt number : Calculation of Nu/Sh : • Isolated droplet : Correlation of Ranz and Marshall (1952) • + Film theory (Abramzon and Sirignano , 1989) - Monodisperse streams : Interaction effects Need of a correction

  13. Evolution of the fluxes Energy balance: Flux (mW) 30 25 Heat transfer from the environment 20 Vaporization flux: 15 C0=9,8 V0=5,6 ms C0=8,2 V0=5,8 ms 10 C0=5 V0=7,2 ms Sensible heat C0=6,6 V0=6,3 ms 5 Loss of enthalpy by shrinkage: t (ms) 0 0 1 2 3 4 5 6 7

  14. L Interactions between droplets Nu/Nuiso 1.4 1.2 1 0.8 Nusselt number 0.6 D 0.4 ( iso : isolated droplet C 0.2 0 2 4 6 8 10 12 14 16 18 Sh/Shiso 1.4 1.2 1 0.8 Sherwood number 0.6 0.4 C 0.2 0 2 4 6 8 10 12 14 16 18 Normalization by the isolated droplet model

  15. II- Evaporation of multicomponant droplets Supported by the French ASTRA program “Experiments and simulation of multicomponent droplets evaporation”

  16. Case of binary droplets: fluorescence intensity Laser intensity Optical constant Composition Tracer concentration Temperature dependence Fluorescence intensity Collection volume c volume fraction of one component (ethanol)

  17. Two equations Two unknown parameters Measurement principles Ifi : Fluorescence intensity over the ith band of detection

  18. 1- Sensitive to composition Low sensitive to T 2- Sensitive to composition Mildly sensitive to T Sensitivity to temperature and composition Acetone-Ethanol mixture,c0=60% 3- Sensitive to composition Very sensitive to T Sensitivity of fluorescence emission to temperature T and ethanol volume fraction c as a function of the wavelength

  19. Experimental set-up 100 150 200 250 300 350 400 450 500 550 Notchfilter Neutral beamsplitter] Collectionoptic D I.F. 3 [570nm 590nm] L Incident laser beams I.F. 2 [535nm 545nm] PMT 3 Hot air plume Desintegration PMT 2 I.F. 1 [525nm 535nm] PMT 1 Heated Air PMT = PhotomultiplicatorIF = Interference filter Thermocouple Injector

  20. Comparisons experiments/simulations T (°C) 30 28 26 24 22 20 18 16 14 0 2 4 6 8 10 12 14 16

  21. 1500 bars t = 9.6 ms 100 T (°C) 50 110 90 70 50 30 10 0 -50 -100 -100 -50 0 50 100 Conclusion Many other possible application of the 2-color LIF thermometry : - Measurements in diesel sprays - Heat advection within droplets - Droplet impingement onto heated surface Twall = 400°C (Thomas Liénart)

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