optical methods for monitoring gas turbine...

© University of Reading 2006 www.reading.ac.uk

Optical methods for monitoring gas turbine emissions

Moira Hilton

J.J.Thomson Physical Laboratory, The University of Reading, Whiteknights, Reading, RG6 6AF

[email protected] 0118 378 8539

2NPL Optical Radiation Measurement Club 27 June 2007

Measurements of Gas Turbine Engine Emissions

– Background and motivation

– ICAO regulations current instrumentation

– Extractive probe measurements

– Non contact spectroscopic methods developed– under EU projects AEROJET 1 & 2

» Gases – FTIR spectroscopy» UHC – FTIR spectroscopy» Particles – Laser Induced Incandescence

– In-flight measurements

– Conclusions


International Civil Aviation Organization Aircraft emissions monitoring

The LTO cycle


Typical exhaust emission levels civil aircraft

• CO2 0.25 - 5%• CO 0- 500 ppm• NO 0- 750 ppm• NO2 0- 50 ppm• H2O 0- 8%• UHC0- 100 ppm• Particulates SN (smoke number) ~2

• Exit temperature(max) 1000 K• Exit pressure 1 bar (above ambient)• Exit velocities 150 - 300 m/s


International Civil Aviation Organization

Aircraft emissions monitoring

Regulations for LTO cycle• Sea level static engine testing• Sample extracted from exhaust stream no further

downstream than one exhaust nozzle diameter• Sample transfer to instruments through line heated to 160 oC• CO2, CO Non dispersive IR• Total UHC Flame ionisation detector• NOx Chemiluminescence• Particulates/Smoke Filter paper discolouration


Test bed aeroengine emissions monitoringJet pipe nozzle

Probe


Probe intrusive measurements(a)

0.00.51.0

1.52.0

-500 -250 0 250 500Distance [mm]

% C

O2

0

100

200

300

-500 -250 0 250 500Distance [mm]

ppm

CO

(b)

05

10

1520

-500 -250 0 250 500Distance[mm]

ppm

NO

(c)

0.00.10.2

0.30.4

-500 -250 0 250 500Distance [mm]

ppm

NO

2

(d)

0

10

20

30

-500 -250 0 250 500Distance [mm]

ppm

C H

C

(e)

300

400

500

600

-500 -250 0 250 500Distance [mm]

T st

at K

(f)

0.00.51.01.52.02.5

-500 -250 0 250 500Distance [mm]

% C

O2

(g)

02040

6080

-500 -250 0 250 500Distance [mm]

ppm

CO

(h)

010203040

-500 -250 0 250 500Distance [mm]

ppm

NO

(i)

0.00.51.01.52.02.5

-500 -250 0 250 500Distance [mm]

ppm

NO

2

(j)

0.02.04.06.08.0

10.0

-500 -250 0 250 500Distance [mm]

ppm

C H

C

(k)

200300400500600700

-500 -250 0 250 500Distance [mm]

T st

at K

(l)

0.0

1.0

2.0

3.0

-500 -250 0 250 500Distance [mm]

% C

O2

(m)

05

10

1520

-500 -250 0 250 500Distance [mm]

ppm

CO

(n)

0

50

100

150

-500 -250 0 250 500Distance [mm]

ppm

NO

(o)

0

2

4

6

-500 -250 0 250 500Distance [mm]

ppm

NO

2

(p)

02468

10

-500 -250 0 250 500Distance [mm]

ppm

C H

C

(q)

200300400500600700

-500 -250 0 250 500Distance [mm]

T st

at K

(r)

From:- “Non-intrusive optical measurements of aircraft engine exhaust emissions and comparison with standard intrusive techniques” Schäfer et al. Applied Optics vol 39, no 3,Jan 2000,pp 441-455


Test bed aeroengine emissions monitoring


Rotating multi-hole cruciform rake probe

3m



2 of 4 rotating manifold arms

Bypass air duct

Core hot gas flow


Free standing probe system mounted externally to engine


EU funded projects

• AEROJET 1 and 2 (1996 - 2001)– Non intrusive measurements of aircraft exhaust emissions

• European Coal and Steel Community (1999-2002)– Electric Arc Furnace control of post combustion CO measurements

using FTIR spectroscopy

• ROSE - Remote Optical Sensing Evaluation (2001-2004)

• AEROTEST (2004-2007) – Remote Sensing Technique for Aeroengine Emission Certification and

Monitoring


Intrusive sampling• Single point or averaged• High cost ~ £ 250,000 probe

system + installation• Complexity of calibration,

data collection and analysis• Potential for losses /

chemistry in heated lines• Time delay between sampling

and analysis - purging ~2mins• Potential distortion of flow

fields

Non intrusive FTIR spectroscopy

•Averaged over line of sight

•Order of magnitude cost reduction

•All species measured simultaneously

•Simpler data collection system

•Species measured in situ - no losses

•Measurements over short timescales ~ 1min

•No distortion of flow fields


Passive emission of thermal radiation using FTIR (Fourier Transform Infrared Spectroscopy)

Jet pipe nozzle

Probe

FTIRTraversable

Periscope


Mattson FTIR mounted on engine test bed


Mattson Research Series FTIR spectrometer


Passive and active modes of operation


Typical aeroengine emission spectrum

Unicam RS FTIR

InSb LN2 cooled

0.25 cm-1 spectral resolution


Avon engine spectrum


Family of spectra for different lines of sight


Analysis of spectra

•Radiance calibration of FTIR with black body•Determine gas temperature from saturated CO2 band of spectrum•Isolate regions of spectrum for analysis of individual species•Generate synthetic spectra of known concentration single species components at calculated temperature•Radiative transfer calculations through multiple layers•Convolve modeled spectra with Instrument Line Shape and fit to experimentally observed data


Temperature calibration using CO2 band


Example of engine test CO retrievals using AEROJET softwar

CO profiles (White cell + FTIR) - N3

0

5

10

15

20

25

30

35

-450 -350 -250 -150 -50 50 150 250 350 450

X mm

CO

ppm

Intrusive sampling

FTIR inversion


Comparison of intrusive and non-intrusive measurements using 4 different FTIR systems

65 70 75 80 85 90 95

8.00E+018

1.00E+019

1.20E+019

1.40E+019

1.60E+019

1.80E+019

2.00E+019

intrusive measurements FTIR measurements

CO2 column densityco

lum

n de

nsity

[cm

-2]

engine power [% NH]

From:- “Non-intrusive optical measurements of aircraft engine exhaust emissions and comparison with standard intrusive techniques” Schäfer et al. Applied Optics vol 39, no 3,Jan 2000,pp 441-455


AEROTEST – enhanced detection of CO with optical filter

2

2.1

2.2

2.3

2.4

2.5

2.6

2160216521702175218021852190219522002205

Wavenumber

Emitt

ance

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

Emitt

ance

No FilterFilter


Aeroengine non-intrusive emissions monitoring instrumentation

• Passive emission Long path absorption (+Band Pass Filter)

• CO2 all levels FTIR • CO >~20 ppm FTIR <~20ppm • NO >~20ppm FTIR <~20ppm • NO2 ? MCT detector• H2Oall levels FTIR • UHC >~ 100 ppm FTIR <~100ppm

• Smoke Laser Induced Incandescence (LII)


Unburnt Hydrocarbon (UHC) inversion

• IR spectra of UHC relatively insensitive to temperature / spatial distribution

• UHC emission in ~ 3000 cm-1 band detected in engine exhaust only in high concentrations - need multipass absorption to detect low concentrations

• Analysis of engine exhaust samples shows alkenes are dominant species

• Lab experiments on emission / absorption of hexene show similar characteristics to engine exhaust spectra

• Inversion by reference to training set of alkene(s) of known concentration versus Total Hydrocarbon Analyser response


Heathrow – British Airways noise pen

31m

88 m


Heathrow –position of IR source and FTIR


UHC band changes with time


UHC downstream of BA747 G-BDXL


TEM of particulate from aeroengine exhaust

100 nm


SMPS size distribution of undiluted aeroengine exhaust

0.00E+002.00E+064.00E+066.00E+068.00E+061.00E+071.20E+071.40E+071.60E+071.80E+072.00E+07

10 100 1000

Diameter (nm)

No.

Con

c. /c

m^3


Laser Induced Incandescence (LII)

Nd Yag Laser

CCD camera

De-tuner

Gas Turbine Engine

Probe


Comparison of LII and SMPS particle measurements

0

1

2

3

4

5

6

7

1 1.5 2 2.5 3 3.5 4

Inte

nsity

(mV)

0.00E+00

2.00E+12

4.00E+12

6.00E+12

8.00E+12

1.00E+13

1.20E+13

1.40E+13

1.60E+13

Vol.

Con

c. n

m^3

/cm

^3

LII signal

SMPS VolumeConcentration

Take OffCruiseIdle


C130 Hercules aircraft - Snoopy

Endurance 12 h (with IFR reserves) Range 5,500 km at 7,000 m alt. Max. altitude 33,000 ft Min. altitude 50 ft (17 m) over water 100 ft (35 m) over land Speed 50 - 150 m/s Scientific payload 17,000 kg with full fuel Crew 5 aircrew + up to 15 scientists


Installation of the FTIR spectrometer


Selection of field of view using 3 mirror system


Fields of view of mirrors

M 3

M 2

M 1 2.4m D/S exhaust

3m D/S exhaust

3.6m D/S exhaust


Typical family of spectra from 3 mirrors

180020002200240026002800

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Altitude 24,000 ft High power low air speed

Wavenumbers

Emittance

M3 2.4m D/S exhaust

M2 3m D/S exhaust

M1 3.6m D/S exhaust


Flight trial outcomes

• Successful demonstration of installation and operation of FTIR in aircraft

• Collection of IR plume spectra along multiple lines of sight and hence tracking of plume evolution

• Evaluation of the effect of altitude, airspeedand engine running condition on exhaust plume IR

• Acquisition of dataset for IR plume reference purposes


Achievements of non-intrusive techniques

– Open path FTIR spectroscopy• Lab instruments works in hostile environments• Single (cheap) instrument can simultaneously

measure nearly all the combustion species of interest• Passive technique / easy to acquire spectra• In flight monitoring capability• Determination of temperature and concentration

gradients in plumes without sampling – Laser Induced Incandescence

• LII improves sensitivity (~ 1000 x dynamic range of Smoke Number filter paper method)


Limitations of the technique

• Radiance calibration of high temperature gases• Modelling spectral line intensities - inadequacy of current

databases• Effect of turbulence / flow fields /dynamic effects - FTIR scan

times too long• Comparison between line of sight optical measurements and

point sampling difficult• Intrinsic IR activity of some molecules low e.g. NO2 and

prone to interference from other species eg H2 O• Passive thermal IR emission monitoring only works with hot

gases - cooler ones need absorption mode


Non-intrusive optical gas turbine engine emissions monitoring – the future

• Single instrument for all gas species• Replacement of conventional extractive sampling • More emissions testing of development engines -

better engines• Environmental studies - plume dispersal• Detection of transient species• Greater understanding of environmental effects of

aviation


Acknowledgements• EU funded projects AEROJET 1 & 2, AEROTEST• EPSRC and NERC• QinetiQ /DSTL - Chris Wilson, Mike Miller, Martin

Fair• Rolls Royce - John Black, Roger Burrows• Met Research Flight • Reading University – Mark Johnson, Mike Welch,

Giovanni Arrigone, Ian Thomas, Brian Everett


AEROJET 2 team at Farnborough test bed

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