Real-time Diagnostics of Jet Engine Exhaust
Plumes, Using a Chirped QC Laser Spectrometer
Kenneth G. Hay, Geoffrey Duxbury, and
Nigel Langford
Department of Physics, University of Strathclyde,
John Anderson Building, 107 Rottenrow, Glasgow, G4 0NG,
UK
[email protected]
Mark. P Johnson and John Black
Rolls Royce Plc, PO Box 31, Derby DE24 8BJ
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Outline of Talk
• Intra-pulse Quantum Cascade laser
spectrometer
• Resolution of Intra-pulse spectrometers
• Jet engine measurements
• Future developments?
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Spectrometer using pulsed quantum cascade
lasers:The Intra-Pulse Method
•
Apply a 50 - 2000 ns top hat
current pulse to a DFB QC
laser.
•
Obtain a light pulse in time
domain with a frequency
down chirp.
•
Pass pulse through
absorbing species and
monitor pulse absorption in
time domain.
•
Laser and Vigo MCT detector
both Peltier cooled, no liquid
nitrogen needed
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Advantages of Intra-pulse Method
• Real time display of absorption spectra.
• Monitor time evolution of samples
• Large frequency sampling window per pulse.
• Multiple species detection and identification
•
•
•
•
•
Rapid collection of data
Short pulse duration minimises vibration noise.
Chirped pulse eliminates fringing in multiple pass cell.
Top hat pulse generation straightforward.
Simple.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
The 3 band of CF3CH3. A comparison
of QC spectrum and that of an FTS,
resolution 0.0018 cm-1.
Transmission, FTS
Bruker FT spectrometer, 5cm path length
1
1
0.4 Torr
0.92
QC spectrometer 60 m path length
0.03 Torr
1
0.5
1278.5
1278
1277.5
1277
-1
Wavenumber/ cm
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Transmission
QC spectrum
0.2 Torr
The
broad
feature
is a hot
band Q
branch
The 3 band of CF3CH3.
Expanded section with slow chirp, ca 20
MHz/ns,of QC laser
Transmission (scaled)
1.04
Note:
similarity of
resolution:
1
0.96
0.92
slight rapid passage
shape of QC spectra
Red QCL
Black FTS
0.88
1277.2
1277
1276.8
1276.6
-1
Wavenumber/ cm
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Exploration of the combustion
products in the exhaust of a gas
turbine
A double pass arrangement was used to measure the
absorption within the exhaust. A vertical translation of
the beam allowed the variation of the absorption.
Path length through exhaust ca.1 m.
Gauze
Attenuator
Retroreflector
Air Flow
Exhaust Plume
Detector
June 22nd 2010
Laser
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Time dependence of the absorption lines after
ignition.
(a) First second following ignition.
(b) First 4 seconds showing
minor bands in the CO2
spectrum
increasing then decreasing.
(c) Next 20 seconds, showing
new absorption lines, possibly
due to water on the right hand
side.
(d) Engine on steady condition at
12,700rpm, exhaust
temperature
969 K, showing lines of CO
and H2O.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Approach to steady state at 12,700 rpm
(c) Next 20 seconds,
showing new
absorption lines,
possibly due to
water on the right
hand side.
(d) Engine on steady
condition at
12,700rpm, exhaust
temperature
969 K, showing
lines of CO and H2O
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Variation of the Hitran absorption cross sections
of CO, CO2 and H2O with temperature.
Note the absorption cross sections
of H2O and CO increase, whereas
that of CO2 decreases.
This makes CO2 difficult to
detect in the hot exhaust gases on
steady condition.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Variation of the relative peak height of spectra of CO
and H2O during a scan through the cross section at
12,800 rpm.
Strong CO and H2O lines
Weak pair of CO and H2O lines
In both examples the CO signal does not increase in magnitude when
the centre of the plume is sampled, whereas that of H2O does.
This suggests that the CO is in the outer part of the plume, but the
water is found in the outer part and the core.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Schematic diagram of the cross section scans at 12,800 rpm.
In both examples the
CO signal does not
increase in
magnitude when the
centre of the plume
is sampled, whereas
that of H2O does.
Strong CO and H2O lines
Weak pair of CO and H2O lines
This suggests that the CO is in the outer part of the plume, but the
water is found in the outer part and the core.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
Conclusions
•Spectrometers based upon the intrapulse method are
very useful for gas sensing
•They can operate in a noisy environment such as that
of a jet engine test cell such as that at RR Ansty.
•The rapid acquisition of a single spectrum in 1 to 2
microseconds minimises the effects of acoustic noise
•They have high sensitivity and good (for rapid
measurement systems) frequency coverage so that
several species may be measured simultaneously.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
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Acknowledgements
We are indebted NERC for the award of a COSMAS
grant and to the EPSRC for an instrumentation grant,
and for the award to K.G. Hay of a studentship
through the Doctoral Training Fund
GD is grateful to the Leverhulme Trust for the award of an
Emeritus Followship during which this project was carried
out.
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m
References
[1] Geoffrey Duxbury, “Infrared Vibration-Rotation Spectroscopy: From Free Radicals
To The Infrared Sky”, Wiley, 2000
[2] G. Duxbury, N. Langford, M.T. McCulloch and S. Wright, “Quantum cascade
Semiconductor nfrared and far-infrared lasers: from trace gas sensing to non-linear
optics ”, Chem. Soc. Rev., 34, 921-934 (2005)
[3] M.T. McCulloch, N. Langford and G. Duxbury,”Real-time trace-level detection of
carbon dioxide and ethylene in car exhaust gases”. Appl. Optics 44, 2887-2894 (2005)
[4] A.Cheesman, J.A. Smith, M.N.R. Ashfold, N. Langford, S. Wright and G. Duxbury, “Application of a
quantum cascade laser for time-resolved, in situ probing of CH4/H2 and C2H2/H2 gas mixtures during
microwave plasma enhanced chemical vapor deposition of diamond”, J. Phys. Chem A 110, 2821-2828
(2006)
[5] K.G. Hay, S.Wright, G. Duxbury and N. Langford, “In flight measurements of ambient methane, nitrous
oxide and water using a quantum cascade laser based spectrometer”, App. Phys. B90, 329-337 (2008)
[6] J. Ma, A. Cheesman, M.N.R. Ashfold, K G. Hay, S. Wright, N Langford,
G Duxbury, and and Y.A. Mankelevich , “Quantum cascade laser investigation of CH4 and C2H2
interconversion in hydrocarbon/H2 gas mixtures during microwave plasma enhanced chemical vapor
deposition of diamond”, J. App. Phys. 106, 033305 (1-15) (2009)
[7] N. Tasinato, G. Duxbury, N. Langford and K G. Hay, “An investigation of collisional processes in a
Dicke narrowed transition of water vapor in the 7.8m spectral region by frequency down-chirped
quantum cascade laser spectroscopy,” J. Chem Phys. 132, 044316 (2010)
June 22nd 2010
65 OSU Mol. Spect. Symp.TE08
10:47 a.m