June 22nd 2010 65 OSU Mol. Spect. Symp.TE08 10:47 a.m Real-time Diagnostics of Jet Engine Exhaust...

June 22nd 2010 65 OSU Mol. Spect. Symp.TE08 10:47 a.m

Real-time Diagnostics of Jet Engine Exhaust Plumes, Using a Chirped QC Laser Spectrometer

Kenneth G. Hay, Geoffrey Duxbury, and Nigel LangfordDepartment of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow, G4 0NG, UK [email protected]

Mark. P Johnson and John BlackRolls Royce Plc, PO Box 31, Derby DE24 8BJ


Outline of Talk• Intra-pulse Quantum Cascade laser

spectrometer

• Resolution of Intra-pulse spectrometers

• Jet engine measurements

• Future developments?


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


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.


The 3 band of CF3CH3. A comparison of QC spectrum and that of an FTS,

resolution 0.0018 cm-1.

The broad feature is a hot band Q branch

12771277.512781278.5

Wavenumber/ cm -1

QC spectrometer 60 m path length0.03 Torr

0.2 Torr

Bruker FT spectrometer, 5cm path length

1

0.5

1

1

0.920.4 Torr


The 3 band of CF3CH3. Expanded section with slow chirp, ca 20

MHz/ns,of QC laser

Note: similarity of resolution:

slight rapid passage shape of QC spectra

0.88

0.92

0.96

1

1.04

1276.61276.812771277.2

Wavenumber/ cm-1

Red QCL

Black FTS


Exploration of the combustion products in the exhaust of a gas

turbineA 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.

LaserDetector

RetroreflectorGauze Attenuator

Exhaust Plume Air Flow


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.


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


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.


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.


Schematic diagram of the cross section scans at 12,800 rpm.

Strong CO and H2O linesWeak 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.

In both examples the CO signal does not increase in magnitude when the centre of the plume is sampled, whereas that of H2O does.


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.


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.


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 7.8m 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 Real-time Diagnostics of Jet Engine Exhaust...

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Transcript of June 22nd 2010 65 OSU Mol. Spect. Symp.TE08 10:47 a.m Real-time Diagnostics of Jet Engine Exhaust...