Optical methods for monitoring gas turbine emissions

Transcription

1 Optical methods for monitoring gas turbine emissions Moira Hilton J.J.Thomson Physical Laboratory, The University of Reading, Whiteknights, Reading, RG6 6AF Tel University of Reading

2 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 2

3 International Civil Aviation Organization Aircraft emissions monitoring The LTO cycle 3

4 Typical exhaust emission levels civil aircraft CO % CO ppm NO ppm NO ppm H2O 0-8% UHC0-100 ppm Particulates SN (smoke number) ~2 Exit temperature(max) Exit pressure Exit velocities 1000 K 1 bar (above ambient) m/s 4

5 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 5

6 Jet pipe nozzle Test bed aeroengine emissions monitoring Probe 6

7 Probe intrusive measurements (a) % CO Distance [mm] (b) ppm CO Distance [mm] (c) ppm NO Distance[mm] (d) ppm NO Distance [mm] (e) ppmc HC Distance [mm] (f) T stat K Distance [mm] (g) Distance [mm] % CO2 (h) ppm CO Distance [mm] (i) ppm NO Distance [mm] (j) Distance [mm] ppm NO2 (m) % CO Distance [mm] (k) Distance [mm] ppmc HC (n) ppm CO Distance [mm] (l) Distance [mm] T stat K (o) ppm NO Distance [mm] (p) ppm NO Distance [mm] (q) Distance [mm] ppmc HC (r) Distance [mm] 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 T stat K 7

8 Test bed aeroengine emissions monitoring 8

9 Rotating multi-hole cruciform rake probe 3m 9

10 Rotating multi-hole cruciform rake probe 10

11 Rotating multi-hole cruciform rake probe 2 of 4 rotating manifold arms Bypass air duct Core hot gas flow 11

12 Free standing probe system mounted externally to engine 12

13 EU funded projects AEROJET 1 and 2 ( ) Non intrusive measurements of aircraft exhaust emissions European Coal and Steel Community ( ) Electric Arc Furnace control of post combustion CO measurements using FTIR spectroscopy ROSE - Remote Optical Sensing Evaluation ( ) AEROTEST ( ) Remote Sensing Technique for Aeroengine Emission Certification and Monitoring 13

14 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 14

15 Passive emission of thermal radiation using FTIR (Fourier Transform Infrared Spectroscopy) Jet pipe nozzle FTIR Traversable Periscope Probe 15

16 Mattson FTIR mounted on engine test bed 16

17 Mattson Research Series FTIR spectrometer 17

18 Passive and active modes of operation 18

19 Typical aeroengine emission spectrum Unicam RS FTIR InSb LN2 cooled 0.25 cm-1 spectral resolution 19

20 Avon engine spectrum 20

21 Family of spectra for different lines of sight 21

22 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 22

23 Temperature calibration using CO 2 band 23

24 Example of engine test CO retrievals using AEROJET softwar CO profiles (White cell + FTIR) - N3 35 Intrusive sampling FTIR inversion CO ppm X mm 24

25 Comparison of intrusive and non-intrusive measurements using 4 different FTIR systems CO 2 column density 2.00E+019 intrusive measurements FTIR measurements 1.80E+019 column density [cm -2 ] 1.60E E E E E 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

26 AEROTEST enhanced detection of CO with optical filter No Filter Filter Emittance Emittance Wavenumber 26

27 Aeroengine non-intrusive emissions monitoring instrumentation Passive emission CO2 all levels FTIR Long path absorption (+Band Pass Filter) 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) 27

28 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 28

29 Heathrow British Airways noise pen 88 m 31m 29

30 Heathrow position of IR source and FTIR 30

31 UHC band changes with time 31

32 UHC downstream of BA747 G-BDXL 32

33 TEM of particulate from aeroengine exhaust 100 nm 33

34 SMPS size distribution of undiluted aeroengine exhaust No. Conc. /cm^3 2.00E E E E E E E E E E E Diameter (nm) 34

35 Laser Induced Incandescence (LII) De-tuner Nd Yag Laser Probe Gas Turbine Engine CCD camera 35

36 Comparison of LII and SMPS particle measurements Intensity (mv) Idle Cruise LII signal SMPS Volume Concentration Take Off 1.60E E E E E E E E E+00 Vol. Conc. nm^3/cm^3 36

37 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 m/s Scientific payload 17,000 kg with full fuel Crew 5 aircrew + up to 15 scientists 37

38 Installation of the FTIR spectrometer 38

39 Selection of field of view using 3 mirror system 39

40 Fields of view of mirrors 3.6m D/S exhaust 3m D/S exhaust M 1 2.4m D/S exhaust M 2 M 3 40

41 Typical family of spectra from 3 mirrors Altitude 24,000 ft High power low air speed E m i t t a n c e M3 2.4m D/S exhaust M2 3m D/S exhaust M1 3.6m D/S exhaust Wavenumbers 41

42 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, airspeed and engine running condition on exhaust plume IR Acquisition of dataset for IR plume reference purposes 42

43 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) 43

44 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. NO 2 and prone to interference from other species eg H 2 O Passive thermal IR emission monitoring only works with hot gases - cooler ones need absorption mode 44

45 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 45

46 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 46

47 AEROJET 2 team at Farnborough test bed 47