Droplet temperature measurement by Laser Induced Fluorescence

by Guillaume Castanet*

*Guillaume.Castanet@ensem.inpl-nancy.fr

Christophe Maqua

Fabrice Lemoine

Industrial burners

Heat engines Aeroengines

Context – Spray applications in combustion processes

Pollutants (NOx. HAP. CO. Soots.…)

Heat

Unburnt products

Atomization Local air/fuel ratio

Aims Optimization of the combustion efficiency

Reduction of pollution

Combustion of monodisperse droplet streams

Membrane

Water circulation for thermal regulation

Piezoceramic

Monodisperse stream

Rayleigh instability

Heated coil (combustion igniter)

Laminar flame

Fuel inlet

-Diameter -Interdroplet distance -Velocity -Temperature

Separation of parameters

Steady phenomenon

time

I- Measurement Technique

Laser excitation

Induced fluorescence

Liquid +

fluorescent tracer

Neglected absorption (short optical path in a droplet)

Optical constant

Laser intensity

Tracer concentration

Measurement volume

Dependence on temperature

( ) ( )( )

0 0T

fluo cI K I C V eβ λ

λ λ=

11 2

2

/'0

2

1/

0

c

c

T

T

I V C eR K eI VK e

KC

ββ β

β

−

= = T

•  Ratio of the fluorescence intensity on 2 bands

•  Fluorescence intensity

Two-color laser induced fluorescence

Measurement volume = Vdroplet I Laser beam I Vcollection

2nd band (>570 nm) 1st band 525-535 nm)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

510 530 550 570 590 610 630 650 670

Laser line (514,5 nm)

Selection of the spectral bands of detection

T=57°C

T=36°C

T=25°C

λ (nm)

Inte

nsity

(A.U

.)

-200

300

800

1300

1800

2300

β (K-1)

Temperature sensitivity β(λ)

Emission spectrum of rhodamine B dissolved in ethanol

( ) ( )( )

0 0T

fluo cI K I C V eλ λ=β λ

Fluorescence emission law in liquids:

Channel 1 Channel 2

PMT 2

PMT 1 Notch filter

Fluorescence +

Scattered light

Interference filter [525 nm ; 535 nm]

Interference filter [>570 nm]

PDA velocity + diameter

Acquisition board

Analog filters with selectable frequency

Amplificators

λ=514.5 nm

Laser beams

Experimental Setup

Dichroic beam splitter

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

L

D LCD

=Injection

Combustion of ethanol droplet streams

Heated coil igniting the combustion

Electrodes for the electrostatic deviation of the drops

C=6,6

C=14.1

C=11.5

C=18.4 C=16.7

C=9.1

flame

0,4

0,5

0,6

0,7

0,8

0,9

1

0 2 4 6 8 10 12

V/V0

t (ms) 0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 2 4 6 8 10 12

(D/D0)2

t (ms)

D0 about 85 µm Velocity Diameter

gur

Vur

dVm T mgdt

= − −

2 212

T V R Cdρ π=

2 2 '0D D K t= −

Velocity and size measurements

C=8,2 V=5,8 ms C=9,8 V=5,6 ms C=14,6 V=5 ms

C=5 V=7,2 ms C=6,6 V=6,3 ms

- Limited influence of C - More noticeable influences of D and V

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12

j5j6

j7j8

j9j1j2j3

D=85,3 µm, C=5, V=7,3 m/s D=85,2 µm, C=6,6, V=6,3 m/s D=85,4 µm, C=8,2, V=5,8 m/s

D=85,4 µm, C=9,8, V=5,6 m/s D=82,7 µm, C=14,6, V=5 m/s D=110,4 µm, C=4,5, V=6,7 m/s D=108 µm, C=4, V=4,6 m/s D=104,8 µm, C=4,2, V=8,2 m/s

t (ms)

0

0éq

T TT T−

−

D0=85,3 µm, C0=5, V0=7,3 m/s D0=85,5 µm, C0=6,6, V0=6,3 m/s D0=85,4 µm, C0=8,2, V0=5,8 m/s D0=85,4 µm, C0=9,8, V0=5,6 m/s D0=82,7 µm, C0=14,6, V0=5 m/s D0=110 µm, C0=4,5, V0=6,7 m/s D0=108 µm, C0=4, V0=4,6 m/s D0=104,5 µm, C0=4,2, V0=8,2 m/s

Equilibrium phase Heating phase

t (ms)

0

0éq

T TT T−

−

Teq»60°C <Tboiling

Volume averaged temperature measurements

Overall energy balance

= −L C vapQ Φ Φ

QL : Internal heat flux entering into the droplet

Φvap : Evaporation flux

vap vL mΦ = & ( )0m >&

ΦC : Convective heat flux between the droplet and the gaseous phase

(radiation neglected)

- Isolated droplet : Correlation of Ranz and Marshall (1952) + Film theory (Abramzon and Sirignano , 1989)

- Monodisperse streams : Interaction effects

Calculation of Nu/Sh :

Need of a correction

( ),

g

s r R

amb s

TD

rNu

T T>

∂ ⎞⎟∂ ⎠

=−

( )C g amb sD T T Nuπ λΦ = −

( ),

, ,

C

s r R

C amb C s

YDr

ShY Y

>

∂ ⎞− ⎟∂ ⎠=

−

g g Mm D D B Shπ ρ=&

Nusselt number : Sherwood number :

0

0,005

0,01

0,015

0,02

0,025

0,03

0 1 2 3 4 5 6 7

flux convectif j8Flux d'échauffement j8Flux d'évaporation j8Flux de fuite j8

0

0,005

0,01

0,015

0,02

0,025

0,03

0 1 2 3 4 5 6 7

flux convectif j8Flux d'échauffement j8Flux d'évaporation j8Flux de fuite j8

Vaporization flux:

Heat transfer from the environment

Sensible heat

Loss of enthalpy by shrinkage:

t (ms) 0

5

10

15

20

25

30

0 1 2 3 4 5 6 7

Flux (mW)

C0=5 V0=7,2 ms C0=6,6 V0=6,3 ms

C0=8,2 V0=5,8 ms C0=9,8 V0=5,6 ms

vL m&

mdTmCpdt

CΦ

( )m sCp T T m− − &

( )& &mC v m s

dTΦ = L m+mCp -Cp T -T mdt

Energy balance:

Evolution of the fluxes

Interactions between droplets

Sh/Shiso

C 0

0.2 0.4 0.6 0.8

1 1.2 1.4

2 4 6 8 10 12 14 16 18

Sherwood number

Nu/Nuiso

C 0

0.2 0.4 0.6 0.8

1 1.2 1.4

2 4 6 8 10 12 14 16 18

Nusselt number

( iso : isolated droplet

L

D

LCD

=

Normalization by the isolated droplet model

II- Evaporation of multicomponant droplets

Supported by the French ASTRA program

“Experiments and simulation of

multicomponent droplets evaporation”

Fluorescence intensity

( )fI λ =

Optical constant

( )optK λ

Tracer concentration

C

Laser intensity

0I

Collection volume

cV

Temperature dependence

( ),Te

β λ χ

( ),γ λ χ

Composition

Case of binary droplets: fluorescence intensity

χ volume fraction of one component (ethanol)

( )( )

( )( )

( ) ( )2 121 1212

12 2 1

ln ln ref ref

ref refref

RR T T

γ χ β χγ χ β χγ χ γ χ

⎛ ⎞⎛ ⎞⎜ ⎟= + −⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

( )( )

( )( )

( ) ( )3 232 2323

23 3 2

ln ln ref ref

ref refref

RR T T

γ χ β χγ χ β χγ χ γ χ

⎛ ⎞⎛ ⎞⎜ ⎟= + −⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

Measurement principles

Two equations

Two unknown parameters

( ) ( ) ( )i j i jβ χ β χ β χ= −iij

j

IfRIf

=

Ifi : Fluorescence intensity over the ith band of detection

0

1000

2000

3000

525 545 565 585 605 625 645 6650

1

2

3

4

5

6

7

8

9

10

( ) ( )0, ,γ λ χ γ λ χ

30%χ =

60%χ =

90%χ =

20%χ =

40%χ =

80%χ =( )nmλ

( ) ( ), Kβ λ χ 1- Sensitive to composition Low sensitive to T

Sensitivity to temperature and composition

2- Sensitive to composition Mildly sensitive to T

3- Sensitive to composition Very sensitive to T

Sensitivity of fluorescence emission to temperature T and ethanol volume fraction χ as a function of the wavelength

Acetone-Ethanol mixture, χ0=60%

Incident laser beams

Desintegration

Injector Thermocouple

Collection optic

100 150

200

250

300

350

400

450

500

550

( )T Co

D

L Vr

Heated Air

Hot air plume

PMT 1

PMT 2

PMT 3

I.F. 1 [525nm 535nm]

I.F. 2 [535nm 545nm]

I.F. 3 [570nm 590nm]

Neutral beamsplitter]

Notch filter

PMT = Photomultiplicator IF = Interference filter

Experimental set-up

( )t ms

T (°C)

Comparisons experiments/simulations

230 , 9 / , 3.8D m V m s Cµ= ≈ =

100%χ =75%χ =50%χ =25%χ =00%χ =

100%χ =75%χ =50%χ =25%χ =00%χ =

230D mµ=Experiment

Model

14 16 18 20 22 24 26 28 30

0 2 4 6 8 10 12 14 16

100%χ =

75%χ =

50%χ =

25%χ =

00%χ =

Conclusion

Many other possible application of the 2-color LIF thermometry :

- Measurements in diesel sprays

- Droplet impingement onto heated surface

- Heat advection within droplets

t = 9.6 ms 100

50

0

-50

-100 -100 -50 0 50 100

32 34 36 38 40 42 44 46 48 50T(°C)

1500 bars1500 bars

110 90 70 50 30 10

T (°C)

1500 bars

(Thomas Liénart)

Twall = 400°C

III- Modeling of the internal advection

Internal temperature distribution measurement

convergent lens ( f = 80 mm )

Laser beams

y

z

volume seen by the collection optics

collection x excitation

volume

y measurement volume z

collection x

68 µm

20 µm

D » 200 µm

droplet

motion

Beams refraction

Jet axis

Trajectory of the beams intersection

Beams refraction

Jet axis

Trajectory of the beams intersection

Beams refraction

Jet axis

Trajectory of the beams intersection

Beams refraction

Jet axis

Trajectory of the beams intersection

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 500.7

0.75

0.8

0.85

0.9

0.95

1

1- Signal processing

Fluorescence intensities

(geometrical optics/GLMT) 3- Axisymetry

2- Positioning

Blind zone

4- Interpolation

time

T Channel 1

Channel 2

Map realization

Internal temperature distribution measurement

5.3 ms

6.9 ms

8.6 ms 9.6 ms

time t = 5.3 ms

100

50

0

-50

-100 -100 -50 0 50 100

t = 5.9 ms 100

50

0

-50

-100 -100 -50 0 50 100

t = 6.9 ms 100

50

0

-50

-100 -100 -50 0 50 100

t = 8.6 ms 100

50

0

-50

-100 -100 -50 0 50 100

t = 8.9 ms 100

50

0

-50

-100 -100 -50 0 50 100

t = 9.6 ms 100

50

0

-50

-100 -100 -50 0 50 100

Motion of the droplet

Application to the case of a monodisperse stream

32 34 36 38 40 42 44 46 48 50 T ( ° C)

Conditions: D0=216 µm, T0=38°C and V0=9.2 m/s

r (µm)

y (µ

m)