12/8/2015
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
then there is also interaction between the chemistry and
the turbulent flow
Turbulence
Chemical reactions
Inter‐
action
Flow‐field equations
(Navier‐Stokes)
Transport equations
for species
1
12/8/2015
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
2
12/8/2015
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
Height above burner (1 mm/div)
C2H2/O2 flame
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
3
12/8/2015
Thermometry in sooty flames
How can we measure the
temperature in this flame?
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.
Photo: Per-Erik Bengtsson
Planck radiation
The spectral shape of the emission is temperature dependent
4,5E+11
T=1600K
T=2000K
4E+11
3
Planck´s law
I ( ) 
Intensity (W/m )
3,5E+11
Photo: Per-Erik Bengtsson
2hc 2
1
5
e hc / kT  1
3E+11
2,5E+11
2E+11
1,5E+11
Wien´s displacement law
1E+11
maxT  2.898 10 3 K  m
5E+10
0
400
Stefan-Boltzmanns law:
I  T 4
800
Visible region
1200
1600
2000
2400
2800
Wavelength (nm)
Per-Erik Bengtsson
4
12/8/2015
Temperature imaging using 2‐D pyrometry
Temperature map
The ratio between the
emission signals at
two wavelengths is
temperature
dependent.
CCDCamera 2
Optical filter
=400 nm
CCD-Camera 1
Optical filter
=470 nm
Still there is a
line-of sight limitation!
Introduction to laser‐based combustion diagnostics
5
12/8/2015
Why use lasers in combustion research?
Photos by P.‐E. Bengtsson
Photo by H. Bladh
•
Nonintrusive
•
High spatial resolution (<0.001 mm3)
•
High temporal resolution (<10 ns)
•
High spectral resolution (~MHz)
•
Multiplex (multi-species, multi-point)
Undisturbed pre‐
mixed flame
Premixed flame
disturbed by a thermocouple
What can be measured with laser‐based combustion diagnostics?
• Temperatures (rotational/vibrational)
• Species concentrations (atoms, molecules, radicals)
• Velocities
• Particle number densities/diameters
• Surface characteristics
6
12/8/2015
Laser techniques used in combustion research Incoherent techniques
Spectrograph &
detector
Laser
Lens
Coherent techniques
For example
• Mie/Rayleigh scattering •
•
•
•
Laser‐induced fluorescence (LIF)
Laser‐induced incandescence (LII)
Laser‐induced phosphorescence (LIP)
Raman scattering
For example
•
•
•
•
Coherent anti‐Stokes Raman
scattering (CARS)
Polarization spectroscopy (PS)
Degenerate four‐wave mixing
(DFWM)
Stimulated Emission (SE)
Laser‐induced fluorescence (LIF) is the most widely used laser diagnostic for combustion studies
Rapid development of lasers and detectors over the last decades
has made LIF a very powerful tool in both fundamental and
applied combustion research
Simultaneous OH‐LIF and PIV measurements in a
turbulent CH4/H2/N2/air flame
125 sec between images, Image size: 14  16 mm
Joakim Bood
7
12/8/2015
Laser‐induced fluorescence ‐ basics
A
A
J’ = 2
J’ = 1
J’ = 0
Potential energy
v’ v’
X
De’’
J’’ = 2
J’’ = 1
J’’ = 0
v’’
v’’ = 0
 fluorescence
spectrum
Internuclear distance
re’’
v’’ = 1
X
Fluorescence spectrum and excitation spectrum
Fluorescence spectrum
Excitation spectrum
A
A
J’ = 2
J’ = 1
J’ = 0
J’ = 2
J’ = 1
J’ = 0
v’
Fluorescence spectrum
v’
Excitation spectrum
v’’ = 1
X
v’’ = 1
X
J’’ = 2
J’’ = 1
J’’ = 0
v’’ = 0
Laser tuned to a specific absorption line and the spectrometer is scanned
J’’ = 2
J’’ = 1
J’’ = 0
v’’ = 0
Laser is tuned across the various absorption lines and the total fluorescence is monitored
8
12/8/2015
2‐D measurements using planar laser‐induced fluorescence (PLIF)
Side view
Sheet-forming optics
OH-PLIF image
View from above
Multi‐species imaging with planar laser‐induced fluorescence (PLIF)
9
12/8/2015
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
Multi‐species imaging in laminar flame
OH CH CH2O Toluene
20
10
12/8/2015
Multi‐species imaging in turbulent flames
Jet speed 60m/s
OH
CH
CH2O
CH
Jet speed 120m/s
CH2O
Toluene
OH
CH
CH2O
CH
CH2O
Toluene
Sjöholm et al., Proc. Combust. Inst. 34, 1475-1482 (2013).
Improved sensitivity using Alexandrite laser
• 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!
Alexandrite (BeAl2O4:Cr3+)
energy level scheme
2
Rapid nonrad. decay
3
pumping
Lasing
(700-820 nm)
4
1
Rapid relax
Strong potential for CH (doubling) and HCO (tripling) PLIF
imaging by long pulse and broadband excitation to avoid
saturation
11
12/8/2015
Spectral investigation of CH‐PLIF
23
CH visualization
Motivation:
Approach:
Intermediate species in NOx formation
Flame front marker
Excitation B  X at ~ 387 nm
Emission B  X, A  X at ~430 nm
Broadband excitation
Co-axial jet flame
CH-PLIF
Excitation scan over band head
Thanks to long and broad pulse ~
two orders of magn. increased
sensitivity compared with conv.
Nd:YAG/dye system (~25 mJ)
Li et al., Proc. Comb. Inst. 31, 727 (2007)
12
12/8/2015
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
13
12/8/2015
Simultaneous PLIF imaging of CH and CH2O
Burner
Flames
PLIF images (CH anf CH2O)
Li et al. Comb. and Flame, 2010
Simultaneous imaging of CH, CH2O, and OH in a turbulent flame
Phi=1.0, Ujet = 100 m/s; Ka ~90
14
12/8/2015
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.
15
12/8/2015
Two‐line LIF thermometry
2
Basic idea:
To measure the relative population
of two states  T from Boltzmann
expression
F21 12
02
F20
Excitation to the same upper state 
F21 and F20 are equally affected by
quenching and energy transfer processes
0
E1  E0  k
T
ln
1

F21
I
 ln 12  4 ln 21  ln C
20
F20
I 02
C non-dimensional system
Dependent calibration constant
Two‐Line Atomic Fluorescence (TLAF) thermometry
Burner
Cylindrical
Quartz plate telescope
P
P
Power meter
Interference filter
ND filter
Dye cell
Quartz plate
CCD-camera
Laser systems
16
12/8/2015
High‐speed imaging
Different approaches for high-speed visualization
• Multi YAG/framing camera approach
Ordinary Nd:YAG laser
t
Nd:YAG laser cluster
Lens mount
Optional image
intensifier
Beam splitter
or
Iris
M
irr
CCD 1
Frame store
CCD 2-6
MCP 8
CCD 8
Mass storage
max rep. rate:
max pulse energy
or
Specs.
Beam splitter optics
irr
M
• kHz laser/CMOS high‐speed camera approach
MCP 1
t
~200 kHz (8 pulses),
~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
17
12/8/2015
High-speed PLIF imaging with multi-Nd:YAG cluster
First objective: Temporally resolved OH
visualization
More recent work: CH visualization
100 µs
∆t = Δt
125=µs
1
5
Turbulent non-premixed
CH4/air flame, Re=5500
CH4 Air CH4
2
3
4
6
7
8
Pumping an OPO  30 mJ/pulse at 430 nm
Bunsen burner flame
Courtesy: J. Sjöholm 2010
C.F. Kaminski et al. Appl. Phys. B 68, 757 (1999)
Multi-YAG applications
Single-cycle-resolved engine diagnostics using PLIF
Fuel-tracer PLIF (fuel: iso-octane, tracer: 6% 3-pentanone)
7o
7.75o
8.5o
9.25o
10o
10.75o
11.5o
12.25o
OH-PLIF
Courtesy: J. Hult, M. Richter
18
12/8/2015
The multi‐YAG‐cluster also opens up for single‐
shot 3‐D measurements • Information on “flame” topology
• Rapid slicing of the measurement volume
• 3-D data reconstructed from the eight resulting 2-D
measurements
3‐D fuel tracer PLIF in an engine
1 2 3 4
5 6 7 8
Sheet spacing: 0.5 mm
Iso‐concentration surface
Measurement
at +6 CAD
Isolated fuel islands
Nygren et al . 29th Comb Symp.
19
12/8/2015
High‐speed simultaneous CH2O/OH PLIF Experimental setup
High‐speed simultaneous CH2O/OH PLIF Preliminary results
Phi=0.6,120m/s,20us OH&CH2O
35
30
40
35
30
0
5
horizontal location/mm
-5
Phi=0.6,120m/s,80us OH&CH2O
30
-5
0
5
horizontal location/mm
30
-5
0
5
horizontal location/mm
40
35
30
-5
0
5
horizontal location/mm
Phi=0.6,120m/s,120us OH&CH2O
45
distance abouve the nozzle/mm
distance abouve the nozzle/mm
35
35
0
5
horizontal location/mm
45
40
45
40
Phi=0.6,120m/s,100us OH&CH2O
45
Phi=0.6,120m/s,60us OH&CH2O
45
distance abouve the nozzle/mm
40
-5
distance abouve the nozzle/mm
Phi=0.6,120m/s,40us OH&CH2O
45
distance abouve the nozzle/mm
distance abouve the nozzle/mm
45
distance abouve the nozzle/mm
Phi=0.6,120m/s,0us OH&CH2O
40
35
30
-5
0
5
horizontal location/mm
40
35
30
-5
0
5
horizontal location/mm
20
12/8/2015
Thanks for your
attention!
For further information contact
[email protected]
21