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Combustion Applications JOAKIM BOOD | DIV. OF COMBUSTION PHYSICS, LUND UNIVERSITY
CH CH2O OH
Combustion processes are very complex The chemistry is extremely complicated…
The most important reaction paths in acetylene oxidation is shown below
Turbulence Chemical reactions
Flow-field equations (Navier-Stokes)
Transport equations for species
Inter- action
then there is also interaction between the chemistry and the turbulent flow
Outline • Multi-spectral imaging concepts based on spontaneous
flame emission
• Introduction to laser-based combustion diagnostics
• Multi-species imaging with planar laser-induced fluorescence (PLIF)
• Two-dimensional thermometry using PLIF
• High-speed imaging
Multi-spectral imaging concepts based on spontaneous flame emission
Spontaneous flame emission (chemiluminescence) Images of Bunsen-type flames having different fuel/air-mixtures
Flame emission spectrum recorded with spectrograph
Spectrum recorded with Ocean Optics HR2000 spectrometer. It is not corrected for the wavelength-dependent variations in sensitivity (i.e. the intensity scale is not calibrated).
Multi-color imaging of flame emission
Setup Result
This is a line-of-sight imaging technique. Three-dimensional information requires tomographic inversion from multi-projection recordings.
C2 470 nm
OH 308 nm
CH 432 nm
C2H2/O2 flame
Heig
ht a
bove
bur
ner (
1 m
m/d
iv)
Thermometry in sooty flames
Total signal intensity depends on both soot volume fraction and temperature. We can measure the temperature in a flame if we can detect the emission intensity as a function of wavelength.
How can we measure the temperature in this flame?
Photo: Per-Erik Bengtsson
0
5E+10
1E+11
1,5E+11
2E+11
2,5E+11
3E+11
3,5E+11
4E+11
4,5E+11
400 800 1200 1600 2000 2400 2800
Wavelength (nm)
Inte
nsity
(W/m
3 )
T=1600KT=2000K
Visible region
Per-Erik Bengtsson
Planck radiation The spectral shape of the emission is temperature dependent
112)( /5
2
−= kThce
hcI λλπλ
mK10898.2 3max ⋅⋅= −Tλ
4TI σ=
Planck´s law
Wien´s displacement law
Stefan-Boltzmanns law:
Photo: Per-Erik Bengtsson
CCD- Camera 2
CCD-Camera 1
Temperature map
Optical filter λ=400 nm
Optical filter λ=470 nm
The ratio between the emission signals at two wavelengths is temperature dependent.
Still there is a line-of sight limitation!
Temperature imaging using 2-D pyrometry
Introduction to laser-based combustion diagnostics
• Nonintrusive
• High spatial resolution (<0.001 mm3)
• High temporal resolution (<10 ns)
• High spectral resolution (~MHz)
• Multiplex (multi-species, multi-point)
Why use lasers in combustion research?
Undisturbed pre- mixed flame
Premixed flame disturbed by a thermocouple
Photos by P.-E. Bengtsson
Photo by H. Bladh
What can be measured with laser-based combustion diagnostics?
• Temperatures (rotational/vibrational)
• Species concentrations (atoms, molecules, radicals)
• Velocities
• Particle number densities/diameters
• Surface characteristics
For example • Mie/Rayleigh scattering • Laser-induced fluorescence (LIF) • Laser-induced incandescence (LII) • Laser-induced phosphorescence (LIP) • Raman scattering
Laser Lens
Spectrograph & detector
For example • Coherent anti-Stokes Raman scattering (CARS) • Polarization spectroscopy (PS) • Degenerate four-wave mixing (DFWM) • Stimulated Emission (SE)
Laser techniques used in combustion research
Coherent techniques
Incoherent techniques
Joakim Bood
Laser-induced fluorescence (LIF) is the most widely used laser diagnostic for combustion studies
Simultaneous OH-LIF and PIV measurements in a turbulent CH4/H2/N2/air flame
Rapid development of lasers and detectors over the last decades has made LIF a very powerful tool in both fundamental and
applied combustion research
125 µsec between images, Image size: 14 × 16 mm
X
v’
v’’
re’’
De’’
Pote
ntia
l ene
rgy
Internuclear distance
A
v’
X
A
v’’ = 0
v’’ = 1
J’’ = 0 J’’ = 1 J’’ = 2
J’ = 0 J’ = 1 J’ = 2
⇒ fluorescence spectrum
Laser-induced fluorescence - basics
v’
X
A
v’’ = 0
v’’ = 1
J’’ = 0 J’’ = 1 J’’ = 2
J’ = 0 J’ = 1 J’ = 2
Excitation spectrum Fluorescence spectrum
X
A
v’’ = 0
v’’ = 1
J’’ = 0 J’’ = 1 J’’ = 2
J’ = 0 J’ = 1 J’ = 2
v’
Laser tuned to a specific absorption line and the spectrometer is scanned
Laser is tuned across the various absorption lines and the total fluorescence is monitored
Fluorescence spectrum and excitation spectrum
Fluorescence spectrum
Excitation spectrum
2-D measurements using planar laser-induced fluorescence (PLIF)
Sheet-forming optics
Side view
View from above
OH-PLIF image
Multi-species imaging with planar laser-induced fluorescence (PLIF)
Setup for multi-species imaging
Toluene CH2O OH CH
Exc. (nm) 266 355 309 431
Det. (nm) 275-290 385-500 309±5 431±10
OH CH CH2O Toluene
20
Multi-species imaging in laminar flame
Jet speed 120m/s Jet speed 60m/s
Sjöholm et al., Proc. Combust. Inst. 34, 1475-1482 (2013).
Multi-species imaging in turbulent flames
OH CH
CH2O CH
CH2O Toluene
OH CH
CH2O CH
CH2O Toluene
• Tunable (740-790 nm)
• High pulse energy: ~400 mJ @ 776 nm, ~ 70 mJ @ 387 nm, ~10 mJ @ 259 nm
• Long pulse length: ~150 ns • Single mode (~100 MHz linewidth) • Multimode (~ 8 cm-1 linewidth) • Example: 5 mJ single mode at 226 nm!
Strong potential for CH (doubling) and HCO (tripling) PLIF imaging by long pulse and broadband excitation to avoid saturation
Improved sensitivity using Alexandrite laser
1
2
3
4
pumping Lasing
(700-820 nm)
Rapid non-rad. decay
Rapid relax
Alexandrite (BeAl2O4:Cr3+) energy level scheme
23
Spectral investigation of CH-PLIF
CH visualization
Thanks to long and broad pulse ~ two orders of magn. increased sensitivity compared with conv. Nd:YAG/dye system (~25 mJ)
Co-axial jet flame
Motivation: Intermediate species in NOx formation Flame front marker Approach: Excitation B ← X at ~ 387 nm Emission B → X, A → X at ~430 nm Broadband excitation
Excitation scan over band head CH-PLIF
Li et al., Proc. Comb. Inst. 31, 727 (2007)
Simultaneous PLIF imaging of CH and OH CH OH
Excitation (nm) ∼387 ∼283
Detection (nm) ∼430 ∼310
CH OH
Simultaneous CH/CH2O PLIF
Li et al., Combustion and Flame 157, 1087-1096 (2010). 26
Li et al. Comb. and Flame, 2010
Simultaneous PLIF imaging of CH and CH2O Burner Flames PLIF images (CH anf CH2O)
Phi=1.0, Ujet = 100 m/s; Ka ~90
Simultaneous imaging of CH, CH2O, and OH in a turbulent flame
2-D thermometry with PLIF
LIF thermometry
• Any method that reflects the distribution of population over two or more individual vibrational rotational states can in principle be used for temperature measurement. LIF is such a method.
• LIF thermometry restricted to high temperatures if molecular
radicals are employed. For OH temperatures above 1500 K are needed.
• If atomic species, such as metal atoms, are used, these have to
be seeded into the flame or flow. • If LIF was used for concentration measurements it is definitely
convenient to apply it for thermometry too.
Two-line LIF thermometry
0
1
2
λ02
λ12 F21
F20
Basic idea: To measure the relative population of two states ⇒ T from Boltzmann expression
Excitation to the same upper state ⇒ F21 and F20 are equally affected by quenching and energy transfer processes
( )C
II
FF
kEETlnln4lnln
20
21
02
12
20
21
01
+++
−=
λλ C non-dimensional system
Dependent calibration constant
PCylindricaltelescope
CCD-camera
PBurner
Interference filter ND filter
Dye cell
Quartz plate
Quartz plate
Laser systems
Power meter
Two-Line Atomic Fluorescence (TLAF) thermometry
High-speed imaging
• Multi YAG/framing camera approach
• kHz laser/CMOS high-speed camera approach
t
t
Ordinary Nd:YAG laser
Nd:YAG laser cluster
Specs. max rep. rate: ~200 kHz (8 pulses), max pulse energy ~350 mJ/pulse @ 532 nm ~ 220 mJ/pulse @ 355 nm ~ 70 mJ/pulse @ 266 nm Possible to pump dye lasers and OPO units for tunable radiation Multiple dye lasers: 20–30 mJ/pulse @ 283nm One OPO unit: ~10 mJ/pulse @ 283nm
CC
D 1
CC
D 8
Beam
spl
itter
Opt
iona
l im
age
inte
nsifi
er
MC
P 1
MC
P 8
Fram
e st
ore
Mas
s st
orag
e
Iris
Lens
mou
nt
CC
D 2
-6
Mirror
Mirror
Beam splitter optics
Different approaches for high-speed visualization
Turbulent non-premixed CH4/air flame, Re=5500
Air CH4 CH4
C.F. Kaminski et al. Appl. Phys. B 68, 757 (1999) Courtesy: J. Sjöholm 2010
First objective: Temporally resolved OH visualization
More recent work: CH visualization
Δt = 100 µs
Pumping an OPO → 30 mJ/pulse at 430 nm Bunsen burner flame
Δt = 125 µs
1 4 3 2
6 5 7 8
High-speed PLIF imaging with multi-Nd:YAG cluster
Courtesy: J. Hult, M. Richter
Fuel-tracer PLIF (fuel: iso-octane, tracer: 6% 3-pentanone)
OH-PLIF
Multi-YAG applications Single-cycle-resolved engine diagnostics using PLIF
7o 7.75o 8.5o 9.25o 10o 10.75o 11.5o 12.25o
• Information on “flame” topology • Rapid slicing of the measurement volume • 3-D data reconstructed from the eight resulting 2-D
measurements
The multi-YAG-cluster also opens up for single-shot 3-D measurements
1 2 3 4
5 6 7 8
3-D fuel tracer PLIF in an engine
Sheet spacing: 0.5 mm
Measurement at +6 CAD
Iso-concentration surface
Isolated fuel islands
Nygren et al . 29th Comb Symp.
High-speed simultaneous CH2O/OH PLIF Experimental setup
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,0us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,20us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,40us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,60us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,80us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,100us OH&CH2O
-5 0 5
45
40
35
30
horizontal location/mm
dist
ance
abo
uve
the
nozz
le/m
m
Phi=0.6,120m/s,120us OH&CH2O
-5 0 5
45
40
35
30
High-speed simultaneous CH2O/OH PLIF
![Quantitative Analysis of Planar Laser-Induced Fluorescence ... · Thermometry of the current NO-PLIF data, also performed in a previous work [17], showed good agreement with CFD predictions,](https://img.pdfslide.net/doc/110x75/5f0f6d1d7e708231d4441a41/quantitative-analysis-of-planar-laser-induced-fluorescence-thermometry-of-the.jpg)
