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© 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
3NPL Optical Radiation Measurement Club 27 June 2007
International Civil Aviation Organization Aircraft emissions monitoring
The LTO cycle
4NPL Optical Radiation Measurement Club 27 June 2007
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
5NPL Optical Radiation Measurement Club 27 June 2007
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
6NPL Optical Radiation Measurement Club 27 June 2007
Test bed aeroengine emissions monitoringJet pipe nozzle
Probe
7NPL Optical Radiation Measurement Club 27 June 2007
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
8NPL Optical Radiation Measurement Club 27 June 2007
Test bed aeroengine emissions monitoring
9NPL Optical Radiation Measurement Club 27 June 2007
Rotating multi-hole cruciform rake probe
3m
10NPL Optical Radiation Measurement Club 27 June 2007
Rotating multi-hole cruciform rake probe
11NPL Optical Radiation Measurement Club 27 June 2007
Rotating multi-hole cruciform rake probe
2 of 4 rotating manifold arms
Bypass air duct
Core hot gas flow
12NPL Optical Radiation Measurement Club 27 June 2007
Free standing probe system mounted externally to engine
13NPL Optical Radiation Measurement Club 27 June 2007
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
14NPL Optical Radiation Measurement Club 27 June 2007
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
15NPL Optical Radiation Measurement Club 27 June 2007
Passive emission of thermal radiation using FTIR (Fourier Transform Infrared Spectroscopy)
Jet pipe nozzle
Probe
FTIRTraversable
Periscope
16NPL Optical Radiation Measurement Club 27 June 2007
Mattson FTIR mounted on engine test bed
17NPL Optical Radiation Measurement Club 27 June 2007
Mattson Research Series FTIR spectrometer
18NPL Optical Radiation Measurement Club 27 June 2007
Passive and active modes of operation
19NPL Optical Radiation Measurement Club 27 June 2007
Typical aeroengine emission spectrum
Unicam RS FTIR
InSb LN2 cooled
0.25 cm-1 spectral resolution
20NPL Optical Radiation Measurement Club 27 June 2007
Avon engine spectrum
21NPL Optical Radiation Measurement Club 27 June 2007
Family of spectra for different lines of sight
22NPL Optical Radiation Measurement Club 27 June 2007
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
23NPL Optical Radiation Measurement Club 27 June 2007
Temperature calibration using CO2 band
24NPL Optical Radiation Measurement Club 27 June 2007
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
25NPL Optical Radiation Measurement Club 27 June 2007
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
26NPL Optical Radiation Measurement Club 27 June 2007
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
27NPL Optical Radiation Measurement Club 27 June 2007
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)
28NPL Optical Radiation Measurement Club 27 June 2007
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
29NPL Optical Radiation Measurement Club 27 June 2007
Heathrow – British Airways noise pen
31m
88 m
30NPL Optical Radiation Measurement Club 27 June 2007
Heathrow –position of IR source and FTIR
31NPL Optical Radiation Measurement Club 27 June 2007
UHC band changes with time
32NPL Optical Radiation Measurement Club 27 June 2007
UHC downstream of BA747 G-BDXL
33NPL Optical Radiation Measurement Club 27 June 2007
TEM of particulate from aeroengine exhaust
100 nm
34NPL Optical Radiation Measurement Club 27 June 2007
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
35NPL Optical Radiation Measurement Club 27 June 2007
Laser Induced Incandescence (LII)
Nd Yag Laser
CCD camera
De-tuner
Gas Turbine Engine
Probe
36NPL Optical Radiation Measurement Club 27 June 2007
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
37NPL Optical Radiation Measurement Club 27 June 2007
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
38NPL Optical Radiation Measurement Club 27 June 2007
Installation of the FTIR spectrometer
39NPL Optical Radiation Measurement Club 27 June 2007
Selection of field of view using 3 mirror system
40NPL Optical Radiation Measurement Club 27 June 2007
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
41NPL Optical Radiation Measurement Club 27 June 2007
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
42NPL Optical Radiation Measurement Club 27 June 2007
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
43NPL Optical Radiation Measurement Club 27 June 2007
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)
44NPL Optical Radiation Measurement Club 27 June 2007
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
45NPL Optical Radiation Measurement Club 27 June 2007
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
46NPL Optical Radiation Measurement Club 27 June 2007
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
47NPL Optical Radiation Measurement Club 27 June 2007
AEROJET 2 team at Farnborough test bed