from quantum mechanics to auto-mechanics
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Frontiers in Spectroscopy. Ohio State University, March 2004. Nonlinear Spectroscopy:. From quantum mechanics to auto-mechanics. Lecture Outline. Lecture 1: Linear and Nonlinear Optics Nonlinear spectroscopic techniques Lasers for nonlinear spectroscopy - PowerPoint PPT PresentationTRANSCRIPT
Paul Ewart
Oxford Institute for Laser Science
Combustion Physics and Nonlinear Optics Group
From quantum mechanics to auto-mechanics
Frontiers in Spectroscopy. Ohio State University, March 2004
Lecture Outline
• Lecture 1: Linear and Nonlinear OpticsNonlinear spectroscopic techniques
Lasers for nonlinear spectroscopy
• Lecture 2: Basic theory of wave mixingCoherent signal generation
Spectral simulation
• Lecture 3: Spectroscopy and diagnosticsHigh resolution spectroscopy
Combustion diagnostics
DFWM spectroscopy of C2 in oxy-acetylene flame
DFWM spectrum of C2 in oxy-acetylene flame
Note: High spectral resolution High signal-to-noise in luminous environment
515.0 515.2 515.4 515.6 515.8 516.0
Simulation (upper graph)Experiment (lower graph)
Inte
nsi
ty (
arb
. units
)
Wavelength / nm
Simulation of C2 DFWM spectra
515.895 515.900 515.905 515.910 515.915 515.920 515.925
P3(28)P2(29)P1(30)
Simulation Experiment Line positions
Inte
nsi
ty (
arb
. units
)
Wavelength / nm
Effects of incorrect line position on simulation
515.0 515.2 515.4 515.6 515.8 516.0
Simulation (upper graph)Experiment (lower graph)
Inte
nsity
(ar
b. u
nits
)
Wavelength / nm
Improved line positions from DFWM measurements
516.0 516.2 516.4 516.6
Simulation (upper graph)Experiment (lower graph)
Inte
nsi
ty (
arb
. units
)
Wavelength / nm
DFWM Spectra of C2 in oxy-acetylene flame
Swan band (0,0) Band head• Corrected line positions• Coherent addition
Multiplex DFWM spectroscopy in flames
1. Broad laser spectrum overlaps molecular resonances
2. Broadband FWM spectrum recorded on CCD camera
3. Theoretical spectrum fitted to find temperature.
C2 spectrum in oxy-acetylene flame
1
2
3
513.0 513.5 514.0 514.5 515.0 515.5 516.0
0.0
0.2
0.4
0.6
0.8
1.0 Experimental spectrum
Theoretical fit
Laser spectrum
Inte
nsity
(ar
b. u
nits
)
Wavelength / nm
(3)(3)
(3)
(45)(45)
(5)(15)(5)
(5)(15)(15) (10)
(10)
(10)
(35)(35)
(35)(40)
(40)
(40)
(45)P3
R1
R2
R3
P1
P2
Broadband/Multiplex DFWM spectroscopy of C2
Multiplex FWM thermometry in flames
• Time resolved measurement of temperature by single laser shot of broadband modeless laser
• Single shot precision of ~4%
500 1000 1500 2000 2500 30000
10
20
Num
ber
Oxy-acetylene flame, Histogram, 100 single shot spectra
Mean: 2936 K
S.D.: 114 K, 3.9%
Thermometry by multiplex DFWM of C2
Temperature / K
1-D line imaging by FWM
Line imaged on Spectrograph slit
Multiplex FWM along a line
• Line formed by intersecting planar laser beams
• FWM signal is induced by broadband laser
• Signal line is mapped onto spectrograph slit
• Spatially resolved spectra recorded on CCD camera
Simultaneous measurement of Temperature and Concentration of C2 along a line
Spectrum at each position
yields temperature T(x)
Spectral intensity along line
yields concentration
Simultaneous measurement of C2 concentration and temperature along 1-D line
DFWM for detection of NOx in
a firing s.i. engine
Detection of combustion generated
NO in s.i.engine using DFWM
• BOXCARS plates: simple, stable, reproducible alignment of input laser beams.
• Collimated beams in interaction region minimizes noise from windows etc.
DFWM spectrum of NO in firing s.i.
engine (methane/air)
DFWM spectrum of NO in firing s.i. engine (methane/air)
Skip fire 1 in 9Speed 1200 rpmIgnition timing: 40o BTDCLaser timing: BDC
Upper trace:NO absorption(line of sight)
Lower trace:DFWM spectrum(space resolved)
LITGS: Laser Induced Thermal Gratings
LITGS in OH in high pressure CH4/air flame
Recorded using cw Ar-ion Laser:1 Watt in ~ 1 s
Flashlamp pumped dye Laser:106 Watt in ~ 1 s
LITGS using long pulse probe
Temperature precision + 0.1% Pressure precision + 2 %
NO2:N2 5 bar 300K
-0.1
0
0.1R
esid
ua
l
0 200 400 600 800 1000 1200
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Time [ns]
Inte
nsity [a
.u.]
FLPDL PulseDatapoints Model Fit
LITGS in NO2:N2 at 40 bar, 300 K
-5
0
5A
bs
olu
teR
es
idu
al
290 300 310 320 330 340 350 360 370 380280
300
320
340
360
380
Thermocouple Temperature [K]
LIT
GS
De
riv
ed
Te
mp
era
ture
[K
] Line of EqualityLITGS data
-1
0
1
Ab
so
lute
Re
sid
ua
l
0 5 10 15 20 25 30 35 40 450
5
10
15
20
25
30
35
40
45
Dial Gauge Pressure [bar]
LIT
GS
De
riv
ed
Pre
ss
ure
[b
ar]
Line of EqualityLITGS data
Simultaneous measurement of Temperature and Pressure along a line
using LITGS
Streak image of LITGS signal from line: NO2 in N2 at 2.5 bar
Time nsec 0 120
Pos
ition
x
Oscillation frequency yields Temperature, T(x)Decay function in time yields Pressure, P(x)
5 mm
Time [ns]
Po
sit
on
[m
m]
0 50 100 150 200 250 300 350
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50
50
100
150
200
250
300
350
400
Position [mm]
Tem
pera
ture
[K
]
0 1 2 3 4 5292
294
296
298
300
302
LITGS: Laser Induced Thermal Gratings
TGV, Thermal Grating Velocimetry
TGV in NO2 seeded air flow
• Thermal grating written by two beams at 532 nm
• Signal read by delayed pulses at 1064 nm from SLM laser
• Forward and Back scattered signals are Doppler shifted up and down in frequency by
TGV air flow measurements
Conclusions
• Laser Induced Grating techniques:
• Temperature CARS
• Minor Species, Temperature DFWM
• 1-D Concentration and Temp. DFWM
• Velocity LITGS
• Pressure and Temperature LITGS
• 1-D Pressure and Temperature LITGS
Acknowledgements
• Karen Bultitude• Rob Stevens• Geraint Lloyd• Radu Bratfalean• Andrew Grant• Duncan Walker• University of Heidelberg PCI• University of Stuttgart, ITV and DLR• EPSRC, British Gas, Rover plc
Potential of LITGS diagnostics
• Non-invasive temperature and pressure measurement
• Time and space resolved data
• Detection of local temperature and pressure
• Diagnostics of auto-ignition and engine “knock”
Schlieren film of autoignitionCourtesy of Prof CWG SheppardUniversity of Leeds