lecture 14: applications of lif, plif of small molecules · lecture 14: applications of lif, plif...

Lecture 14: Applications of LIF, PLIF of Small Molecules

Planar Laser Induced Fluorescence

1. Intro to LIF & PLIF imaging applications

2. Flame applications of OH PLIF

3. PLIF with molecular vibrations in IR

4. Imaging hypersonic flows – challenges

5. Imaging hypersonic flows – PLIF of OH in reacting and non-reacting flows

6. Imaging hypersonic flows – T and dual species

Planar Laser Induced Fluorescence (PLIF): A two-dimensional image can be acquired using LIF by Using a 2-D detector array (i.e. digital camera) Expanding the excitation laser beam into a sheet

2

1. Introduction to LIF & PLIF Imaging

Laser

IR camera

Sheet opticsFlow facilityFilter

Fluorescence

Display

1-D LIF

PLIF

Pulsed lasers are used to achieve single-shot imaging Shot excitation pulse effectively freezes the flow field Can suffer from lower SNR than 1-D LIF because the laser

energy is spread out over a much larger area May use averaged measurements for improved SNR with either

CW or pulsed laser excitation for steady systems

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1. Introduction to LIF & PLIF Imaging

Laser

IR camera


Fluorescence

Display

3-D PLIF scan laser sheet

Sheet must cross flow field during laser pulse ∆t Depth-of-field of lens must include outermost sheets Camera must frame quickly; #sheet/∆t

Display methods Orthogonal slices (cube display) Surface rendering Movie

4

1. Introduction to LIF & PLIF: 3D-PLIF

Laser

Camera


FluorescenceSpinning mirror

Species density

Assume known: A21, B21;Iν, V & Ω are usually measured (i.e., by Rayleigh scattering)

Then SF ∝ C·ni, where C ∝ VΩfv,J/Q is from a calibration point For T-varying systems, need to select v and J to give fv,J/Q

independent of T5

1. Introduction to LIF and PLIF ImagingApplication of LIF to species density

Measure ni [molecules/cc] with LIF using linear excitation

Q

Tfn

QAABIVnS J

iF,v

2121

2112

01 4

photons/s

nALAP

nLPP

in

inout

scattered WWRayleigh:

intensity II

VIn

nVIP

Woutscattered

set in experiment

measure known

VICan infer

Species mole fraction

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1. Introduction to LIF and PLIF ImagingApplication of LIF to species mole fraction

i

Ji

JiF

XCTTf

X

cnTf

nS

,v

,vphotons/s

Q = nσc, c = mean molecular speed C is obtained by calibration Requires selection of v and J to give Tf

Tf J

,v

Temperature Strategy 1: Single-line method

Strategy 2

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1. Introduction to LIF and PLIF Imaging Application of LIF to temperature

TTf

XS JiF

,v

Use a tracer with fixed Xi

Select v and J for large T dependence of T

f J

,v

TFTfTf

QTf

n

QTf

n

SS

J

J

Ji

Ji

F

F

2,v

1,v

2

,v

1

,v

21

Select λ1 and λ2 to probe states with strong T-dependence for fv,J(T)1/ fv,J(T)2

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1. Introduction to LIF and PLIF Imaging30 Years: From Concept to Standard Tool

1982 – 1st PLIF in flames 1984 – 1st PLIF in turbulent flames 1987 – 3D digital flow field mapping with PLIF1992 – Acetone tracers to visualize flow mixing with PLIF1993 – PLIF investigation of scamjet fuel mixing1996 – PLIF imaging of temperature in supersonic jet2000-present – Transition of tracer-based PLIF imaging into industrial labsWhere is PLIF today:2012 – Use of kHz rate PLIF in practical aeropropulsion problems (e.g., swirl burner)

Now some applications of tracer-based PLIF

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2. Flame Applications for OH PLIF:A Tool for Turbulent Flame Research

Seitzman et al, 23rd International Symposium on Combustion (1990)

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2. Flame Applications for OH PLIF Flame Structure vs Reynolds Number via OH PLIF

OH PLIF of a hydrogen diffusion flame in air (2.2mm diameter jet)

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2. Flame Applications for OH PLIF Diffusion Flame Structure using OH PLIF

OH PLIF to visualize flame structure in a plane vs1. Axial distance from the nozzle exit2. Radial distance from the fuel jet axis

• H2/air diffusion flame• 2.2 mm diameter jet• Re~24,000

@41 D2-41D

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Forced CO2 jet

Infrared Planar Laser-Induced Fluorescence Imaging Potential to image species not easily accessible with Visible/UV PLIF

CO, CO2, H2O, hydrocarbons Advances in IR lasers sources and cameras have made IR PLIF possible First demonstrations of IR PLIF performed at Stanford (Kirby and Hanson)

2.0 μm excitation4.3 μm fluorescence

3. PLIF with Molecular Vibrations in IR

Laser

IR camera

Sheet opticsFlow facility

Filter

Fluorescence

Display

13

Photophysics of Vibrational Fluorescence for CO and CO/CO2 PLIF

Emission rates are low (100 s-1 vs 106 s-1) Energy transfer process can be slow (μs vs. ns) V-V transfer is typically faster than V-T transfer

3. PLIF with Molecular Vibrations in IR

Energy transfer following 2.3 μm excitation of CO:

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Air

CO2 jet425 K

Kirby and Hanson, Appl. Opt., 2000.

Example of CO2 Imaging: Using 10.6 μm Excitation3. PLIF with Molecular Vibrations in IR

Transverse CO2 jet (425K) in air cross flow4.3 μm collection

Demonstrates ability to image hot CO2, mixing Potential for CO2 imaging in flames

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Benchmark lifted CH4 flame studied at Yale allows for quantitative comparisons

IR PLIF agrees with CFD and averaged Raman measurements within 20%

Demonstrates feasibility of single-shot imaging

LIF signal >> Raman

CO2(single-shot)

CO2(36-shot avg)

Raman(Yale)

~5,000 shots per row

CFD(Yale)

combustionproducts

(e.g., CO2)

Air

fuel65% CH4with N2

Air

imaged region(1.7 x 1.7 cm)

laser sheet(3 J @ 10.6)

Comparison of CO2 Images in a Lifted CH4 Flame3. PLIF with Molecular Vibrations in IR

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M > 6

Supersonic Combustor

HYPER-X Autoignition and Flame-Holding Mixing

Research Issues:

High-speed, harsh flow fields require non-intrusive diagnostics

Diagnostic Issues:

How do we do ground test beyond Mach 8?Impulse Facilities: reflected shock tunnels, expansion tubes

Diagnostic Challenges of SCRAMJETS: Opportunities for PLIF

4. Imaging Hypersonic Flows – Challenges

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Driver Section

Driven Section

Expansion Section

Dump Tank

Amplifiers &

Interval Counters

ICCD Camerafor OH-PLIF Imaging

578 x 384 Array

DoubleDiaphragm

8 Channel Data

Acquisition

System

KnifeEdge

YM 1200 Nd:YAG Laser

HD 500 Dye Laser

HT 1000Frequency

Doubler

Long durationXenon Arc

Light Source

DichroicMirror

IMACON 468Ultrafast Framing Camera

for Schlieren Imaging(inc. 8 ICCD modules,

each 576 x 384)

Image Acquisition

Computers

Driven/ExpansionDiaphragm

Mirror 2

Mirror 1

FocusingMirror

Single-shot PLIF imaging 8-frame schlieren imaging

Optical Diagnostics

Stanford Expansion Tube Facility4. Imaging Hypersonic Flows – Challenges

18

N2He Fuel/O2/N2mixture

He

Driversection

Buffersection

Drivensection

Expansionsection

Viewing Section

A Tool to Study Ram Accelerator Phenomena

Virtue of expansion tube: accelerates combustible gas to high velocity, with reduced exposure to high temperatures

M > 1 Projectile Fix projectile, flow gases, employ PLIF

Measurement Strategy

Unsteady combustion/detonationKey issue

5. Imaging Hypersonic Flows – Reacting

19

NO PLIF Imaging of Non-Reacting Flows

Mixture: 0.15% NO + 9.5% CH4 + 90.35% N2

P = 0.063 atm, V = 2230 m/s, M = 7, T = 280 K

19 mm Blunted Cylinder 40 degree Wedge

NO PLIF useful for shock wave visualization and quantitative flowfielddeterminations (T, P, χi)

5. Imaging Hypersonic Flows – Reacting

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V∞ = 2230 m/s , P∞ = 0.07 bar, M∞ = 6.3, T∞ = 300 K

25 mm Spherical-Nosed Cylinder

5% C2H4 + 15% O2 + 80% N2

Mixture CJ velocity, VCJ = 1685 m/stign ~ 1 µs

16.7% CH4 + 33.3% O2 + 50.0% N2

Mixture CJ velocity, VCJ = 1950 m/stign ~ 10 µs

25 mm Spherical-Nosed Cylinder

V∞/VCJ = 1.14 V∞/VCJ = 1.32

PLIF reveals steady combustion Peak OH in stagnation region

5. Imaging Hypersonic Flows – OH PLIF in Reacting FlowsSimultaneous OH PLIF and Schlieren Imaging of Smooth Flame Front Regime: V∞/VCJ >1

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Large Disturbance Regime: V∞/VCJ <1 Comparison with CFD Calculations

T∞ = 300 K, P∞ = 0.5 bar,V∞ = 1760 m/s

Stoichiometric H2/Air

Density contours from A. Matsuo & K. Fujii,AIAA 95-2565

T∞ = 420 K, P∞ = .23 bar,V∞ = 1730 m/s

20 mmDiameter

25 mmDiameter

10% C2H4 + 30% O2 + 60% N2

V∞/VCJ = 0.90V∞/VCJ = 0.90

Experimental results show good agreement with CFD calculations of large disturbance regime

5. Imaging Hypersonic Flows – OH PLIF in Reacting Flows

Model problem: jet in supersonic crossflow

2-D imaging required to capture complex, unsteady flow structure

Defining parameter: jet momentum ratio: J = (ru2)jet/(ru2)∞22

INJECTANT(Hydrogen)

BOW

SHOCK

RECIRCULATION ZONE

M>1

RECIRCULATIONZONE

BOUNDARY LAYERMACH DISK

JET-SHEAR LAYERVORTICES

Autoignition Zones

Critical Scramjet Issue: Mixing of Fuel5. Imaging Hypersonic Flows – Reacting

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M= 3.4V= 2360 m/sP= 0.32 atmT= 1290 K

Instantaneous Average

Use of short gating times reveals unsteady flow structure

0.1 μs exposure8-frame movie with 1ms framing time shows flow structure

10 μs exposure

Nitrogen

Hydrogen

H2 Jet in Supersonic Crossflow Imaging with Schlieren5. Imaging Hypersonic Flows – Reacting

24

PLIF Imaging of OH in Combusting Jet

Mach 13OxygenM∞= 4.7V∞= 3200 m/sP∞= 0.04 atmT∞= 1250 K

H2 , J=5x/d

Mach 10AirM∞= 3.4V∞= 2360 m/sP∞= 0.32 atmT∞= 1290 K

x/dH2 , J=1.4

Penetration increases with jet momentum ratio (J) Increased recirculation zone enhances flame holding Reaction zone width increases with x/d

Key Observations

Sf χOH·f(T)

Defining Eqn:


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Flame Structure of Hydrogen Jet in Supersonic Crossflow(Combine Side-view, Plan-view and Transverse-plane Images)

Flat plate

Illumination sheet

Expansion tube exit

Fuel injection

Flow

xz

y

Schematic diagram of imaging experiments

M = 2.4P = 40 kPaT = 1500 KJ = 2.4

Planar laser-induced fluorescence of hydroxylradical marking the instantaneous reaction zoneof hydrogen jet in supersonic crossflow


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Flame Structure of Hydrogen Jet in Supersonic Crossflow

Plan-views

y/d = 5 y/d = 3

y/d = 1 y/d = 0.5 y/d = 0.25

Images adapted from Heltsley (2009)


27Adapted from Heltsley (2009)

M = 2.4P = 40 kPaT = 1500 KJ = 2.4

Plan-view

Transverse Planeview

Side-view

Flame Structure of Hydrogen Jet in Supersonic Crossflow


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Hydrogen (M = 1)J = 2.4D = 2 mm

AirM = 2.4P = 40 kPzT = 1500 K

OH PLIF images trace the 3-D structure of the flame

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Extension of PLIF Imaging to Scramjet Flow Using 2 Lasers for T

Tk

CSS

Rf

f 1212

2

112 exp

Instantaneous temperature imaging Instantaneous multi-species imaging

H2 jet

Supersonic air

6. Imaging Hypersonic Flows – T w NO (2 camera)

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Instantaneous, Two-Line NO Temperature Images

Instantaneous T determined to ±50 K in 300 K-1400 K range Images reveal:

Jet mixing requires x/d ~ 12 Heated boundary layer provides ignition

With NO in freestream

Without NO in freestream

0 18x/d

0 18x/d

6. Imaging Hypersonic Flows – T w NO (2 camera)

31

Simultaneous NO and OH Imaging

NO

OH

composite

Reveals mixing

Reveals combustion zones

6. Imaging Hypersonic Flows – Dual Species

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Comparison of Axial and Transverse Plane Images

NO

OH

NO image reveals efficient mixing by x/d = 15 OH image reveals that combustion occurs at jet periphery

and in boundary layer

11 mm

x= 22 mm

Freestream: M=1.4, P=0.4 atm, T=2200 K Jet: Po=3 atm, To=300 K, d=2 mm

6. Imaging Hypersonic Flows – Dual Species

Next Lecture

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Applications of LIF and PLIF using flow tracers1. PLIF of ketone hydrocarbons

2. Acetone PLIF to image fuel mixing

3. 3-pentanone PLIF as a flow tracer

4. 3-pentanone PLIF in IC-engines

5. CW PLIF for high frame-rate imaging

6. Toluene PLIF for temperature

7. Two camera toluene PLIF for temperature

lecture 14: applications of lif, plif of small molecules · lecture 14: applications of lif, plif...

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