Download - COMBUSTION DIAGNOSTICS – LIF
SLIDE 1 | JIMMY OLOFSSON | 2013A Nova Instruments company
COMBUSTION DIAGNOSTICS – LIFDr. Jimmy Olofsson
SLIDE 2 | JIMMY OLOFSSON | 2013A Nova Instruments company
Outline
• Why combustion diagnostics?
• Molecular spectroscopy in brief
• Combustion LIF system
• Time-resolved Combustion LIF
• Coffee break
• Applications
• Related Techniques
SLIDE 3 | JIMMY OLOFSSON | 2013A Nova Instruments company
Why combustion diagnostics?
SLIDE 4 | JIMMY OLOFSSON | 2013A Nova Instruments company
Benefits of analysing combustion
Combustion related applications:• Transportation• Electrical power production• Heating
Combustion analysis can be used for economic as well as environmental benefits by:
• Optimizing fuel economy• Improving performance and reliability• Reducing pollutant emissions
SLIDE 5 | JIMMY OLOFSSON | 2013A Nova Instruments company
Benefits of using lasers forcombustion diagnostics
• Non-intrusive• High spatial resolution• High temporal resolution• High sensitivity• Species selective• 2D measurements
Laser-based measurements techniques can provide information on species concentrations, temperature fields, flow velocities etc. and the measurements often have the following properties:
SLIDE 6 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combustion diagnostic techniques
Soot LII
Rayleigh Temperature
Fuel Tracer LIF
Combustion Radicals - LIF
Combined Measurements
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Molecular spectroscopyin brief
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Combustion species
• Gas with chemical reactions• Production of radicals• Qualitative concentration of radical
- OH- CH- NO- etc
• Concentration of larger molecules/tracers- Formaldehyde- Acetone- etc
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Laser-Induced Fluorescence
Excited State
Ground State
Photon
Absorption
Excited Molecule
Emission
Fluorescence
• Species selective measurements (OH, formaldehyde, fuel tracers, etc.)
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Molecular energy states: Electronic
e-
e-
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Molecular energy states:Vibrational and Rotational
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OH absorption spectrumSeveral absorption lines around 283 nm
• Air Wavelengths Excitation in UV
Wavelength (Å)
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OH absorption spectrumTwo narrow absorbtion regions within 100 nm range
240 260 280 300 320 340 360
Wavelength (nm)
0.05
0.04
0.03
0.02
0.01
0.00
Op
tica
l De
nsi
ty
O–H ~283 nm
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Temperature dependence
Choose a peak with for which the fluorescence is independent of temperature
in the measured temperature range
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Acetone absorption spectrumLarger molecules have wider absorption range
240 260 280 300 320 340 360
Wavelength (nm)
0.05
0.04
0.03
0.02
0.01
0.00
Op
tica
l De
nsi
ty
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Selection of excitation wavelength
• To excite atoms or diatomic molecules the laser wavelength must be precisely tuned to match molecular energy transition.
• Larger molecules, such as Acetone, 3-pentanone or Formaldehyde, have many more close-lying states, effectively making a wide continuous absorption band. Therefore, any wavelength within the absorption band can be used to excite the molecule.
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Laser-Induced Fluorescence
0
0,2
0,4
0,6
0,8
1,0
200 250 300 350 400 450 500 550
Wavelength /nm
Fluorescencespectrum
No
rmal
ised
in
ten
sit
y
Bandpass
filter
Laserline
600
Absorptionspectrum
Detected LIF
Residual laser light
SLIDE 18 | JIMMY OLOFSSON | 2013A Nova Instruments company
SLIDE 19 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combustion LIF system
SLIDE 20 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combustion LIF system
CCD Camera
Burner
Nd:YAG Laser
Dye LaserSheet Optics
UV Camera Lens
Optical Filter
Image Intensifier
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Standard Nd:YAG pumped dye laser
Nd:YAG laser• Single cavity 10 Hz• Wavelengths: 1064 nm, 532 nm,
355 nm, 266 nm• Pulse length ~10 ns• Pulse energy 400 mJ @ 532 nm
Tuneable dye laser• Tunability range of fundamental:
380-750 nm• UV extension down to 200 nm• Line width: 0.8 cm-1
• Narrow band option: 0.08 cm-1
1090 mm
840 mm
250 mm
744 mm
250 mm
Nd:YAG laser
Dye laser
3ω/4ω 2ω
Beam combining output bench
Dye laser UV beams or 266nm or
355nm
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Tuneable dye laser oscillator
Dye Laser
4. Flowing dye cell5. High reflectivity mirror6. Focusing lens
1. Tuning mirror2. Grazing incidence
grating3. Beam expander prism
(NBP Option)
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Tuning curves for laser dyes
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Species and excitation wavelengths
SpeciesExcitation
wavelengthLaser pulse
energyProcess Type of dye
OH 283 nm 25 mJ Doubling Rh590
CH 389 nm 28 mJ Mixing Rh610+Rh640
CO 230 nm 13 mJMixing after
doublingRh610
NO 226 nm 4.5 mJMixing after
doublingRH590+Rh610
Our refecence species which we use during the lab training
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Light sheet forming optics
• Quartz optics for UV/visible transmission• Parallel light sheet
- Better control of reflections- Enhanced energy distribution
Beam waist adjusterSheet height adjuster
Holder & fixation system
Standard mount
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Detecting Laser-Induced Fluorescence
Image Intensifier • Image intensifier
- Amplifies the incoming light- Converts UV fluorescence to
visible light detectable by the CCD camera
- Allows gated detection with very short time gates, to minimise detection of natural flame emission
UV Camera Lens
• UV camera lens required for detection of UV fluorescence
Spectral Filter
• Spectral filter to eliminate detection of scattered laser light and flame emission
CCD Camera
• Sensitive, high-resolution CCD camera
SLIDE 27 | JIMMY OLOFSSON | 2013A Nova Instruments company
Optical filters
• Interference filters are used to transmitt only in the wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm
• All other wavelengths should ideally be blocket by the filter
SLIDE 28 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combustion LIF: Software and timing
• Synchronization unit
• Analog Input option. Includes the A/D board and software add-on
• Software:
- DynamicStudio acquisition and processing software
- Software add-ons for tracer LIF and combustion LIF
SLIDE 29 | JIMMY OLOFSSON | 2013A Nova Instruments company
Laser control from the software
Nd:YAG laser• Automatic detecion• Auto activation at
Preview/Acquisition• Q-switch activation/de-activation
during Preview/Acquisition• Interlock messages displayed in
Log
Tuneable Dye laser• Wavelength set• Wavelength fine-tune buttons• Wavelength scan• Output wavelength calculated
from fundamental depending on frequency conversion scheme
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Time-resolved Combustion LIF
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Framing rate requirements
EXAMPLE
• Heat release event in combustion engine running at 1200 rpm.
• The main heat release occurs within ~5CAD out of the entire 360CAD engine cycle.
J.Olofsson et al SAE 2005
Tim
e-r
eso
lved F
orm
ald
ehyde L
IF
• Resolution used in the study: 0.5CAD
• This corresponds to a 14kHz
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High-speed Nd:YLF laser
Output pulse energy (527 nm) vs repetition rate (single cavity laser)
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Pumping of dye lasers
Pumping of a dye laser with high repetition rate causes two major problems:
• Decrease in pulse energy• Deterioration of beam profile
Pulse separation: 75 µs
Rep. Rate: 13kHz
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TR C-LIF: YAG-based pump lasers
IS Series
• Repetition rate up to 10kHz
• Pulse length: ~10ns
• Pulse energy @ 4kHz: 8mJ
HD Series
• Repetition rate up to 10kHz
• Pulse length: ~10ns
• Pulse energy @ 10kHz: 12mJ
• Pulse energy @ 5kHz: 20mJ
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TR C-LIF: Dye laser
Example:
Pumping with 12W @ 1kHz => 12mJ / pulse
Dye: Rhodamine 6G (~570nm) gives 3.3mJ / pulse
Frequency doubling to ~283nm for OH LIF is estimated to give ~0.5mJ / pulse
This should be compared with the corresponding ~20mJ / pulse achieved by the standard 10Hz system!
SLIDE 36 | JIMMY OLOFSSON | 2013A Nova Instruments company
TR C-LIF: SpeedSense camera series
Model example SpeedSense v711
Maximum fps at full res.
7500 at1280 x 800
Resolution at 10kHz (example)
1280 x 600
Resolution at 15kHz (example)
896 x 544
SLIDE 37 | JIMMY OLOFSSON | 2013A Nova Instruments company
TR C-LIF: Image intensifiers
Model H Series9138A1178
Maximum repetition rate
200 kHz
Minimum gate time
10 ns
Diameter (input/output)
24 mm
Photocathode material
Multialkali
Phosphor screen material
P46
L Series9138A1180
100 kHz
40 ns
25 mm
S20(as
Multialkali)
P46
SLIDE 38 | JIMMY OLOFSSON | 2013A Nova Instruments company
SLIDE 39 | JIMMY OLOFSSON | 2013A Nova Instruments company
COMBUSTION DIAGNOSTICS – APPLICATIONSDr. Jimmy Olofsson
SLIDE 40 | JIMMY OLOFSSON | 2013A Nova Instruments company
Mixing and heat transfer Pre- / Post-combustion Combustion
Liquid flowsGaseous flows
(non reactive)
Gaseous flows
(reactive)
Image intensifier unit
Applicat
ions
Hardwar
e
Tuneable Dye LaserNd:YAG Laser
Scalar imaging applications
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Fuel Tracer-LIF
Two different approaches to fuel visualization
• ”Real” fuels- Real engine conditions- Unknown fluorescent
properties (temperature, pressure, quenching etc.)
• Non-fluorescing reference fuel with added fluorescent tracer
- Well-known fluorescent properties
- Allows for quantification- Further from real engine
conditions
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Fluorescent tracer spectra
• Acetone fluorescence spectrum • Formaldehyde fluorescence spectrum
- A: in a flame- B: in an engine
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Application example 1
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How to acheive homogeneous Acetone concentration for calibration
Example:Quantification of fuel vapour in constant pressure vessel using liquid fuel
“Iso-octane was used as substitute of real gasoline in PLIF experiment and 10% acetone was added in as tracer.”
…
“To get a homogeneous mixture, a small amount of fuel was injected into vessel. Waited about 30 seconds for vaporization, then, recorded 100 LIF signal images. After averaged the images and subtracted the background, the result gave the relationship between current equivalence ratio and the LIF signal.”
Tsinghua UniversityBeijing, China
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Tracer-LIF calibration
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Application example 2
SLIDE 47 | JIMMY OLOFSSON | 2013A Nova Instruments company
Formaldehyde visualization in anHCCI engine
Homogeneous Charge Compression Ignition Engine
Advantages• Lower NOx levels and less soot formation
compared to the Diesel engine• Higher part load efficiency compared to the
SI engine
Disadvantage• Difficult to control ignition timing
For some fuels formaldehyde is formed in the cool-flame region
J.Olofsson et al SAE 2005
SLIDE 48 | JIMMY OLOFSSON | 2013A Nova Instruments company
Formaldehyde LIF in an engine
Wavelength: 355 nmFuel: N-Heptane
Field-of-view
J.Olofsson et al SAE 2005
High-speed laser
SLIDE 49 | JIMMY OLOFSSON | 2013A Nova Instruments company
Cycle-resolvedFormaldehyde consumption
Single-cycle-resolved formaldehyde fluorescence imaged with a time separation of ~70 µs (0.5 CAD).
J.Olofsson et al SAE 2005
SLIDE 50 | JIMMY OLOFSSON | 2013A Nova Instruments company
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Fluorescence spectra diatomic radicals
• OH radical
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Application example 3
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PIV/PLIF investigation of two-phase vortex-flame interactions
• Study of two-phase vortex-flame interaction in a counterflow burner
• Local flame extinction events
• PIV for flow velocity field measurements giving the local strain rates
• PLIF of CH (389.5 nm) for diffusion flame front location and flame extinction zones
Investigation done in collaboration between École Centrale Paris, France, Innovative Scientific Solutions, and Wright-Patterson Air Force Base, OH, USA
SLIDE 54 | JIMMY OLOFSSON | 2013A Nova Instruments company
Simultaneous CH PLIF and PIV
By courtesy of
École Centrale Paris, France, Innovative Scientific Solutions, and Wright-Patterson Air Force Base, OH, USA
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Application example 4
SLIDE 56 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combined OH LIF, fuel tracer LIF and PIV
SLIDE 57 | JIMMY OLOFSSON | 2013A Nova Instruments company
Combined OH LIF, fuel tracer LIF and PIV
Simultaneous flow field (PIV), fuel (tracer-LIF) (blue) and OH (LIF) (green) visualisation in a turbulent atmospheric flame. Courtesy of R. Collin and P. Petersson, Division of Combustion Physics, Lund University, Sweden.
OH radical
Fuel tracer / Acetone
Flow velocity field
• Local flame extinction events
• Create a data base of measurement data
• Data used for model comparison
SLIDE 58 | JIMMY OLOFSSON | 2013A Nova Instruments company
Simultaneous PIV and TR OH LIF local flame extinction
BurntCoflow
Unburnt: Methane&Air
Air&Burnt
OH
OH
OH: Intermediate combustion product in hydrocarbon combustion. Flame front marker.
Time-resolved OH LIF at 2.5kHz framing rate
Lund University P.Petersson and J.Olofsson
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Multi-dye laser cluster
J.Olofsson
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Application example 5
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Planar Laser-Induced Fluorescence (PLIF) system
Diode pumped Nd:YAG laser is used to pump a high repetition rate dye laser.
The emitted 283 nm laser pulses excites OH radicals in the flame –> imaged on an intensified high-speed camera.
Combined with high repetition rate Nd:YLF laser for simultaneous TR PIV.
Combined TR PIV and TR OH LIFwith Lund University, Sweden
SLIDE 62 | JIMMY OLOFSSON | 2013A Nova Instruments company
Flow field and flame front at 4 kHz
Lund University P.Petersson and J.Olofsson
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COMBUSTION DIAGNOSTICS – RELATED TECHNIQUESDr. Jimmy Olofsson
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Laser-Induced Incandescence
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Soot in combustion
• Soot is a hazardous pollutant emission
• Soot is related to incomplete combustion which has an impact on combustor performance
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Laser-Indusced Incancescence
• Soot particles are heated up by laser radiation• The increased particle temperature results in increased emission of
Plank radiation
Size decreases
Time (ns)
LII i
nten
sity
(a.
u.)
0 100 200 300 400 500
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LII measurement systems
Image Intensifier
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Application example 6
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Laser diagnostics in an IC engine
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Quantitative LII
Soot-volume-fraction in a Diesel engine
Work done by H. Bladh et al, at Combustion Physics, Lund University, Sweden
Soot
volu
me f
rati
on
(p
pm
)
• Soot formation at different EGR rates
• Soot formation at different piston bowl geometries
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Rayleigh Thermometry
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Rayleigh Thermometry
• The Rayleigh signal is dependent on:
- Laser intensity- Scattering cross section- Number density
• If species composition and pressure are known in the gas the gas temperature can be determined from imaging of the Rayleigh scattering.
SLIDE 73 | JIMMY OLOFSSON | 2013A Nova Instruments company
Required data sets forRayleigh Thermometry
Reference imageMeasurement image
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Results of Rayleigh Thermometry analysis
Mean: 1120 K
RMS: 61,3
Mean: 295 K
RMS: 12,2
Mean: 1350 K
RMS: 106
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Rayleigh Thermometry results
Takes into account:• Scattering cross-section• Pressure• Laser pulse energy
SLIDE 76 | JIMMY OLOFSSON | 2013A Nova Instruments company
Thank you for your attention!
DANTECD Y N A M I C S