development and application of planar laser thermometry in ... · “unstructured les of reacting...
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Dr Dahe Gu DPM, Melbourne, 16 – 18 Oct 2018 Defence Aviation Safety Authority (DASA)
Development and Application of Planar Laser Thermometry in Sooting Flames
Bio
• Education – B.E. (Mech and Aero, Hons) – Ph.D. (Mech) \
• Research experience – laser diagnostics in combustion
• key combustion parameters, e.g. temperature • in-situ, non-intrusive, 2-D and simultaneous techniques
– 11 journal articles, 7 presentations • incl. Combustion and Flames, Proceeding of the Combustion Institute • incl. International Symposium on Combustion, Gordon Research Conference
• Employment – Regulations Officer, Defence Aviation Safety Authority (DASA)
• Personal interest – aviation
University of Adelaide (2008 – 2011) University of Adelaide (2012 – 2016)
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Outline
• Introduction – combustion – temperature (T ) measurements in flames
• Laser diagnostics in turbulent sooting flames – Temperature imaging
• Two-Line Atomic Fluorescence (TLAF) interferences precision and accuracy
– 2-D, in-situ, non-intrusive, instantaneous and simultaneous measurements • temperature (T ), soot volume fraction ( fv ), and particle size (dp )
– algorithm for 2-D image analysis
• Conclusions
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• Combustion – provides > 80% of world energy – complex phenomenon
• hundreds of reacting species • coupled chemical and physical processes
• Combustion devices – hydrocarbons, soot, turbulent – design approach
• modeling & experiment (measurements)
Introduction
• Desirable measurement attributes
– accuracy, precision – 2-D, in-situ, non-intrusive – instantaneous / single-shot (not averaged) – simultaneous measurements – species specific
Ham et al., “Unstructured LES of reacting multiphase flows in realistic gas-turbine combustors,” Annual Research Briefs, Center for Turbulence Research, Stanford University, 2003.
Pratt & Whitney combustor, computational simulation
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Introduction
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Improve precision and accuracy of temperature imaging using TLAF in turbulent sooting flames
• Temperature measurement challenges – typical range: 1,200 – 2,000+ K – intrusive techniques, e.g. thermocouple – non-intrusive techniques, e.g. laser diagnostics
• Laser diagnostics techniques – 2-D, in-situ, non-intrusive, single-shot
• Temperature in combustion – governs combustion process – combustion device design
– Two-Line Atomic Fluorescence (TLAF)
• range: 1,000 – 2,800 K • single-shot precision ~ 100 K in non-sooting flames • suffers from interferences in sooting flames • > 50 % interference in collected emissions
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Flame
Two-Line Atomic Fluorescence (TLAF) Experimental Setup
2 pulsed lasers @ 410 & 451 nm
excite seeded tracer: Indium (In)
laser energy recording
Temperature image Stokes signal Anti-Stokes signal
signal acquisition X2 indium LIF images
@ 451 & 410 nm
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64 mm
• TLAF in sooting flames – lasers excite not only tracer – indium (LIF signals), but also excite other species (interferences)
• unavoidable, details unknown
– significant interferences • > 50% in collected emissions
– interferences from multiple sources • characteristics unknown • spatial, temporal, spectral
Challenges
d
c
b
a
deduced Indium
LIF signal
collected emissions
collected interferences
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• Strategies to improve TLAF in sooting flames
– interference assessment • identify sources • spatial, spectral and temporal characteristics
– means for interference suppression • explore various spatial, spectral and temporal means
– validations • laminar and turbulent sooting flames
o data measured by other methods / simulation results
Methodology
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Interference Assessment
• Interferences assessment results
– sources: (1) PAH-LIF; (2) scattering and; (3) LII from soot particles
– spatially, spectrally and temporally overlapped with indium LIF signals
– comparable to indium LIF signals
– solutions:
o (1) spectral: narrow-band filter with high transmission at indium LIF line;
o (2) temporal: reduced acquisition time: 30 ns (10-9 !)
Spectrograph image for the Stokes transition (excitation wavelength at 410 nm) as collected (a) with prompt timing and (b) with a 50 ns delay.
The cross- sections of prompt spectrograph image at radial distance of 0 mm (c) and 3 mm (d), as indicated by the dashed red lines in (a) and (b). HAB = 22mm.
• Interference assessment
– spatial, spectral and temporal characteristics
• relative to TLAF signals (indium LIF signals)
– experimental design
• spectrometer
• laminar ethylene non-premixed sooting flame
– peak soot volume fraction (max fv): ~ 8 ppm
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Interference Suppression
Narrow-band filters (Alluxa) • bandwidth ~ 1.2 nm • transmission ~ 95% • OD ~ 6 • signal-to-interference ratio (SIR)
o 8 ⎼ 9 times
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Measurement accuracy due to the presence of interferences increases from 200 K to 10K.
Precision of single-shot results increases by ~ 40%.
Validation Laminar Flame
Partially premixed ethylene/air sooting flame
• peak fv ~ 1.2 ppm
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[1] M. Köhler; K. Geigle; T. Blacha; P. Gerlinger; W. Meier, Combustion and Flame 159 (8) (2012) 2620-2635
Comparison between TLAF and CARS results: centreline
Validation Turbulent Flame
450 mm
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[1]
g
f e d c
b a
Comparison between TLAF and CARS results: radial profiles
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c
b
Validation Turbulent Flame
Turbulent Sooting Flame: 2-D measurements temperature (T), soot volume fraction (fv), particle size (dp)
Exit Reynolds number 10,000
Fuel mass flow 10.4 g min-1
Co-flow air mass flow 320 g min-1
Fuel temperature 298 ± 2 K
Ambient temperature 294 ± 2 K
Mean fuel jet velocity 44 ms-1
Lift off height 26.3 ± 3.9 mm
Power 8.7 kW
Flame length ~ 450 mm
Table 1: Operational conditions for the sooting, turbulent non-premixed ethylene flame.
Ethylene turbulent sooting flame
• lifted jet flame
Dataset available [1,2] • soot particle size (dp): simulation • soot volume fraction (fv): LII • temperature (T): CARS – point
2-D simultaneous measurements • T, fv and dp
o dp: time-resolved LII (TiRe-LII) o fv: laser-induced incandescence (LII) o T: TLAF
• 15 heights • correlations between T, fv, dp
[1] M. Köhler; K. Geigle; W. Meier; B. Crosland; K. Thomson; G. Smallwood, Applied Physics B 104 (2) (2011) 409-425 [2] M. Köhler; K. Geigle; T. Blacha; P. Gerlinger; W. Meier, Combustion and Flame 159 (8) (2012) 2620-2635 13
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Turbulent Sooting Flame Results
Turbulent Sooting Flame Results
15 locations
Each location o 499 image sets o 5(radial) x 3(axial) mm2
o 67,365 data points
HA
B (m
m)
1200 1600 2000 2400 Temperature (K)
Soot
vol
ume
frac
tion
(ppm
)
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Correlation between fv and T joint Probability Density Functions (PDFs)
HAB
(mm
)
Correlation between fv and dp joint Probability Density Functions (PDFs)
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Turbulent Sooting Flame Results
HAB
(mm
)
Correlation between fv and T joint Probability Density Functions (PDFs)
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Turbulent Sooting Flame Results
Laminar Flame 2-D Image Analysis
• Identify local flame/soot structure
o soot sheets, e.g. geometry
• Examine correlations between o T, fv, dp
• Understand soot evolution o how fast does soot grow/oxidise? o how does temperature affect soot grow/oxidise?
• Analysis algorithm and processes o identify soot sheets o compute soot sheet skeleton o establish local coordinates o examine correlations
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• Convoluted flame structure
• Employs multiple computations o based on discrete intensity levels
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Turbulent Flame 2-D Image Analysis
Conclusions
Development of TLAF for sooting flames – interference sources identified and characterised – interference suppression means – achieved an accuracy of 10 K – improved precision by 40% reduction in single-shot distribution
Turbulent ethylene non-premixed sooting flame – simultaneous imaging of T, fv and dp – flame centreline and radial profiles – statistical correlations between T, fv and dp
2-D image analysis algorithm (ongoing) – identifies local flame structure – analyse soot sheet – assess correlations between T, fv and dp
– understand soot formation and oxidation
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Acknowledgements
The Australian Research Council
The University of Adelaide
German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt; DLR)
Defence Aviation Safety Authority (DASA)
Question & Answer
Thanks for Your Attention!
Q & A