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)

1

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

2

• 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

2 2

3

2

Introduction

2

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

4

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

5

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

6

• 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

7

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

8

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