12. New techniques
• Measurements in areas with limited optical access– Single ended experiments
• ps-lidar, p ,• Structured illumination
• Measurements in optically dense environment (e.g. sprays)
Ballistic imaging– Ballistic imaging– SLIPI (Structured Laser Illumination Planar Imaging)
• Measurements of ”new” species– Photofragmentation LIF; PF-LIFg ;
Limited optical accessFurnaces, boilers, fires
How can spatially resolved measurementsHow can spatially resolved measurements be made in situations with very limited
ti l ?optical access?
Can a backscattered technique be developed for sub-cm resolution?
• Potential approach: ps-LIDARP t ti l h St t d ill i ti• Potential approach: Structured illumination
LIDAR concept
Basic principle of LIDARZ
Laser
Pulsed laser system
Detector2D measurement
gnal
gnal
1D measurement
posi
tion
Sig
Ti Di t
Sig
Z-p
Time/DistanceTime ~ Distance Time ~ DistanceSignal
Courtesy: Kaldvee and Bood 2010
Lidar equation
RR
bbp dss
RRrnDWRI
02 ,2exp,
• D is a system constant,
• Wp is the transmitted laser pulse energy,
• nb is the number density of scattering objects,
• σb is the backscattering cross section of the scattering objects,
• ∆R is the range resolution of the system depending on the time between the samplings ofdepending on the time between the samplings of the signal
• α is the extinction coefficient.α is the extinction coefficient.
Differential Absorption Lidar (DIAL)p ( )
2121 ,,ln
21
2 RIRIRIRI
RRRRN OFFON
2112 ,,22 RIRIRR ONOFF
C ti l lid 1Conventional lidar 1: SO2 measurements at Etna
Ref: Per Ragnarsson PhD thesis
C ti l lid 2Conventional lidar 2: Hg measurements
Ref: Per Ragnarsson PhD thesis
Conventional LIDAR – ps LIDAR
• Due to a laser pulse of ~10 ns the spatial resolution is ~ 1 5 m far much higher thanresolution is ~ 1.5 m, far much higher than required.
• Using a ps laser (~10ps) the spatial resolution is a couple of mmis a couple of mm.
A d t t lt f t i l• As detector an ultrafast response is also required; a streakcamera.
Streak camera
E i t l t f lidExperimental set-up for ps-lidar (proof of principle)
Streak camera Water aerosolsf = 10 cm
Streak camera Water aerosolsStreak camera Water aerosolsf = 10 cm
CCD Streak tube Lenses
Water aerosols
CCD Streak tube Lenses
Water aerosols
CCD Streak tube Lenses
Water aerosols
Trigger unit
Nebulizerspulse = 30 ps = 532 nm
Delay unitTrigger unit
Nebulizerspulse = 30 ps = 532 nm
Delay unitTrigger unit
Nebulizerspulse = 30 ps = 532 nm
Delay unit
ked
G2
ked
G2
ked
G2
ode-
lock
Nd:
YA
God
e-lo
ckN
d:Y
AG
ode-
lock
Nd:
YA
GM
oM
oM
o
Results
a) Nebulizers positioned 65 cm apart. The range resolution is in this case limited to 3 cm) p p gdue to the slow streak rate (1 ns/mm) of the streak camera necessary to cover atotal measurement range of 3 m. b) Nebulizers localized 7 cm from each other, range resolution is 5 mm set by the pulse duration f th l (30 )of the laser (30 ps).
Laboratory LIDAR feasability studiesRayleigh scattering
Photo: Henrik Bladh
1 D 2 DPhoto: Henrik Bladh
Photo
LIDAR signal
1600 K1800 K1.3
cm
LIDAR signal
Temperatureimage
200 202 204 206 208 210 212 cm1200 K1400 K1600 K
2.7g
< 1000 K
Courtesy: Kaldvee and Bood 2010 Kaldvee et al. Appl. Opt 2009
ps-LIDAR in a fire experiment
Experimental set-up ”DIAL”p p
DIAL results
How can spatially resolved measurementsHow can spatially resolved measurements be made in situations with very limited
ti l ?optical access?
Can a backscattered technique be developed for sub-cm resolution?
• Potential approach: ps-LIDARP t ti l h St t d ill i ti• Potential approach: Structured illumination
Conventional backscattering arrangement
Light that is back-Light that is back-scattered is collected from ALL sections of the samplesample.
NO depth-resolution possiblepossible.
Conventional backscattering arrangement
Light that is back-Light that is back-scattered is collected from ALL sections of the samplesample.
NO depth-resolution possiblepossible.
New backscattering arrangement
Light that is back-scattered is STILLcollected from ALLcollected from ALLsections of the sample.
Depth resolution isDepth-resolution is possible as a section is different from the othersothers.
New backscattering arrangement
Light that is back-scattered is STILLcollected from ALLcollected from ALLsections of the sample.
Depth resolution isDepth-resolution is possible as a section is different from the othersothers.
Stuctured Illumination - Illustration
32131 IIIIC 2/12
322
312
2132 IIIIIIIS 3213C 3
Modulation In focus visible
Out of focusModulation not visiblenot visible
The difference between ”normal” imaging and structured
Courtesy: Elias Kristensson
Three images with the modulation moved. This does not change the image in the lower plane, only in the upper one.
The difference between normal imaging and structured illumination. In the image to the left, the lower plane is still visible, while it is removed in the image to the right.
Experimental Setup
A = aperture, L = lens, SF = spatial filter, M = mirror, R = Ronchi ruling, G = glass plate, BS = beam splitter
Kristensson et al. Appl. Opt . 2008 .
Results
Kristensson et al. Appl. Opt . 2008 .
Depth-resolution
4 mm
Depth-resolution approximately 4 mm
Limited optical access: Engines, gasturbines
Endoscopic hybrid imaging systemFuel +tracer
Simple quartzMultifunctional hybridrela elements (effecti eSimple quartz
endoscope d = 1 cm
relay elements (effective aberration correction)
Beam-shapingendoscope (266 nm)d = 9 mm
Courtesy C. Schultz (C. Gessenhardt, F. Zimmermann, C. Schultz, R. Reichle, C. Pruss and W. Osten, Hybrid endoscopes for laser based imaging diagnostics in IC engines, SAE 2009-01-0655)
Challenges in optical dense mediumChallenges in optical dense medium
• Extinction• Multiple scattering
Possible techniques:Ballistic imaging (Linne et al Proc 32 Comb Symp )Ballistic imaging (Linne et al. Proc. 32 Comb. Symp.)X-ray scattering (Wang et al. Nat. Phys. (2008)Structured laser illumination planar imaging SLIPIStructured laser illumination planar imaging, SLIPI
Motivation
• To burn liquid fuels at an effective rate, the liquidTo burn liquid fuels at an effective rate, the liquid must be rapidly dispersed into the air using a sprayMi t ti i i h bi ff t• Mixture preparation in an engine has a big effect on flame propagation, extinction, and emissions formationformation
• Sprays are complex flow fields that behave quite differently in different flow regimes:- steady or transient spray- ratio of fuel density to gas density- fuel vapor pressurefuel vapor pressure- injector pressure drop- fuel stream Reynolds number- fuel surface tension and viscosity- internal architecture of the injector
Spray fluid-mechanical zonesp y
a liquid core that intrudes into the gas phase- a liquid core that intrudes into the gas phase- a primary breakup region where the liquid core breaks
into large dropletsd b k i h i d l- a secondary breakup region where primary droplets
break into smaller droplets- a vaporization region where the small droplets are
evaporated prior to burning
Meas rements in opticall denseMeasurements in optically dense environment:
- SLIPI
- Ballistic imaging- Ballistic imaging
Examples of planar laser imagesExamples of planar laser images
Aureole of light blurring the image
Wrong light intensity contribution blurring the imagecontribution
Planar Laser Imaging is principally restricted by errors introduced by Multiple Scattering especially in the Dense Spray Regionby Multiple Scattering, especially in the Dense Spray Region
Courtesy: Elias Kristensson, Edouard Berrocal
Scattering from a dense mediumScatte g o a de se ed u
Light is collected from many different sections of thedifferent sections of the sample.
Can be thought of as out ofCan be thought of as out-of-focus light and can be reduced by Structured Illumination!Illumination!.
Courtesy: Elias Kristensson
Experimental set-upp p
• Water spray• Pressure-swirl nozzle• Type: Danfoss 1910• Injection pressure: 50 bars• 50 averaged images• 12-bit intensified CCDs
Kristensson et al. Opt Lett. 2008
Structured Laser lllumination Planar Imaging SLIPIImaging - SLIPI
Ф = 0o Ф = 120o Ф = 240o
2/12
322
312
21 )()()(32 IIIIIIIS
3321 IIIIC
33
The SLIPI technique
Conventional
Berrocal et al. Opt Express. 2008Kristensson et al. Opt Lett. 2008
Meas rements in opticall denseMeasurements in optically dense environment:
- SLIPI
- Ballistic imaging- Ballistic imaging
A diesel spray in the atomization regimep y g• Need direct experimental evidence
regarding breakup of the liquid core at the g g p qexit of a spray
• The centerline of the near field (within 10 orifice diameters) is so dense that most )optical beams are lost
• Light is highly attenuated in turbid media:II
Diesel jets have an optical depth in the
L
o
exteII scattabsext N L
o
exteII scattabsext N , where
- Diesel jets have an optical depth in the range ext L ~ 5 - 15 (one measurement gives ext L = 8), human tissue has ext L = 11
• Need a high-resolution, single-shot imaging system for the liquid core despitethe turbidity of the spray → ballisticthe turbidity of the spray ballistic imaging, a technique originally developed for medical imaging
Mark Linne
Introduction to ballistic imagingg g
input
lightdiff h t
snake-like photonballistic photon
Even in dense media, some photons do not g
diffuse photon scatter, passing directly through the medium – called “b lli ti h t ”
ballisticphotons
diffuse
scattering medium “ballistic photons”
inputpulse
snake-likephotons
diffusephotons
t tBecause they do not scatter, ballistic photons have the
t
pulse photons photons have the shortest path length and exit first
Mark Linne
Transient time-gated ballistic imagingTransient time gated ballistic imaging
it hi b short pass filterpolarizer + rotator (45 )o
switching beam
CS cell2
short pass filter
displayscreen
rotator (45 )
long pass filter
bj timaging beam
CCD
mode-locked f Ti hi
fier
timedelay
object
crossed polarizers
u)
fs Ti:sapphire laser
kHz
ampl
i
OKE gate
2 ps
tran
smis
sion
(au
measured OKE gate
1
-3 -2 -1 0 1 2 3 4 5 6 7 psdelay timeO
KE
Mark Linne
Diesel spray result (1)p y ( )Example ballistic image during
steady periodsteady period
small
100 m
smallvoid
periodicstructure 3.5 mm
liquid
gasphaseliquidphase
Mark Linne
Diesel spray result (2)p y ( )Ballistic images of the spray developing over early
timestimes(times are all given after the start of injection)
a. 2 µs b. 10 µs c. 94 µs d. 980 µs
Mark Linne
”New” species detection”New” species detection
Photofragmentation laser-induced fluorescence (PF-LIF)
1. H2O2 + h→ OH + OH
( )
fluorescence2. OH + h→ OH*
3. OH* → OH + h
OH radical
OH radical
Hydrogen peroxidey g
H2O2 detection using PF-LIF
Excitation scan
Signal vs [H2O2] (g)
Johansson et al., Appl. Spectr. 62, 66-72 (2008).
L hL h
PF-LIF imaging of H2O2Laser sheetsLaser sheets
AirVapor consisting of
H2O and H2O2
AirVapor consisting of
H2O and H2O2
Liquid consisting of50% H2O and 50% H2O2
Liquid consisting of50% H2O and 50% H2O2
Single-shot images
Johansson et al., in The Conference on Lasers and Electro-Optics (CLEO)/The International Quantum Electronics Conference (IQEC) (Optical Society of America, Washington, DC, 2009), presentation CThI4.
Measurement of the total H2O2 + HO2 concentrationH /O flame on welding nozzle ( = 2 2)H2/O2 flame on welding nozzle ( = 2.2)
282 nm
266 nm266 and 282 nmFlame
Image after subtraction of natural OH Comparison with modeling
Application of PF-LIF in a HCCI Engine
Bo Li et al.
PF-LIF Excitation ScanPF LIF Excitation Scan-23 CAD
Bo Li et al.
PF-LIF signal at different CADPF LIF signal at different CAD-23 CAD 12 CADTDC
266+283
283
283 offline
White tip: injectorCircles at each side: valvesCircles at each side: valves
Bo Li et al.
Future laser diagnostic challenges
• Multiple-parameter visualization (, T, v, soot) 4D i li ti (3D t)• 4D visualization (3D + t)
• Accurate species concentration measurements Q tit ti h t i ti f ( /li id• Quantitative characterization of sprays (gas/liquid distribution, temperature, droplet size,,,), dense sprays2D elocit meas rements itho t seeding• 2D velocity measurements without seeding
• Quantitative fuel visualization without seederA t 2D t t t• Accurate 2D temperature measurements
• On/near surface measurements (LIP, FRS, picosec.)S ti ll l d t i i d lid• Spatially resolved measurements using picosecond lidar
• Spatially resolved identification of different HC’s, f G (CO )• Measurements of EGR (CO2)
LIF image of CO2 (at 4.26 m, right) from a 5 mm diameter nozzlea 5 mm diameter nozzle
Acknowledgements• All present and previous members of the
Division of Combustion Physics, LU
• Numerous collaborating patners in Lund, Sweden and internationally
Sponsors
Thank you for listening!
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