15 lecture short course at princeton university€¦ · tunable diode laser applications in ic...

Lecturer: Ronald K. HansonWoodard Professor, Dept. of Mechanical EngineeringStanford University

15 Lecture Short Course at Princeton University

Copyright ©2018 by Ronald K. HansonThis material is not to be sold, reproduced or distributed without prior

written permission of the owner, Ronald K. Hanson.

Underlying Science:Molecular Spectroscopy

Diagnostic Methods:Laser Absorption, LIF

Example Applications:Engines, Shock Tubes, Kinetics

Lecturer: Ronald K. HansonWoodard Professor, Dept. of Mechanical EngineeringStanford University

15 Lecture Short Course at Princeton University

Copyright ©2018 by Ronald K. HansonThis material is not to be sold, reproduced or distributed without prior

written permission of the owner, Ronald K. Hanson.

Today/Lecture 1:• Overview• Introductory Material

Course Objectives and Content• Introduction to fundamentals of molecular spectroscopy & photo-physics

• Introduction to laser absorption and laser-induced fluorescence

• Introduction to shock tubes as a primary tool for studying combustion chemistry, including recent advances and kinetics applications

• Example laser diagnostic applications including:• multi-parameter sensing in different types of propulsion flows and engines• species-specific sensing for shock tube kinetics studies• PLIF imaging in high-speed flows

Next: Spectroscopy and Roles of Lasers

Lecture 1: Course Overview

3

Course Overview:Spectroscopy and Lasers

What is Spectroscopy?• Interaction of Radiation (Light) with

Matter (in our case, Gases)• Examples: IR Absorption

Why Lasers?• Enables Important Diagnostic

Methods• LIF, Raman, LII, PIV, CARS, …• Our Emphasis: Absorption and LIF• Why: Sensitive and Quantitative!

Calculated IR absorption spectra of HBr

1000 1500 2000 2500 3000

0.01

0.1

1

10

100

1000CO2

CH3

C2H4

Min

imum

Det

eciti

vity

[ppm

]

Temperature [K]

1atm,15cm,1MHz

H2ONH2

1000 1500 2000 2500 3000

0.01

0.1

1

10

100

1000

OH

Min

imum

Det

eciti

vity

[ppm

]

Temperature [K]

1atm,15cm,1MHz

CH

CN

Minimum Detectivity using Laser Absorption

4

Spectrally resolved individual absorption line of NO at 600 K, 1 atm (in C2H4 combustion exhaust)

Course Overview:Role of Lasers in Energy Sciences

5

Example Applications:Remote sensing, combustion and gasdynamic diagnostics, process control, energy systems and environmental monitoring.

Common Measurements:Species concentrations, temperature (T), pressure (P), density (ρ), velocity (u), mass flux (ρu).

Coal-fired power plants

Coal gasifiers Swirl burners

IncineratorsOH PLIF in spray flame

Course Overview:Roles of Laser Sensing for Propulsion

TDL Sensing in Pratt & Whitney PDE

@ China Lake, CA

TDL Sensing in SCRAMJET @ WPAFB

Applicable to large-scale systems as well as laboratory science

248 nm beamSignal

PLIF in plume of Titan IV @ Aerojet

PLIF imaging of H2 jet in model SCRAMJET

@Stanford

TDL Sensing in IC-Engines @ Nissan & Sandia

Validate simulations and

models

Characterize test facilities

Understandcomplex reactive

environments

Optical Diagnostics

6

Ring Dye Lasers(UV & Vis)

Diode Lasers(Near IR & Mid-IR)

CO2 Lasers(9.8-10.8 m)

Ti:Sapphire Laser(Deep UV)

He-Ne Laser(3.39 m)

DriverSection

Shock TubeDriven Section

emis

Incident Beam Detector

Transmitted Beam Detector

Diaphragm

7Course Overview:Role of Lasers in Combustion Kinetics: Shock Tubes

High-Speed Camera

EC-QCL Laser(11 m)

Temperature(4.3 m)




emisIncident Beam

Detector


VS

P1T1

P2T2

IncidentShock Wave

8Course Overview:Role of Lasers in Combustion Kinetics: Shock Tubes

EC-QCL Laser(11 m)

He-Ne Laser(3.39 m)


High-Speed Camera

Temperature(4.3 m)




emis

Incident Beam Detector


P5T5

P2T2 VRS

ReflectedShock Wave

Applications of Shock Tubes• Ignition Delay Times• Elementary Reactions• Species Time-Histories

Species Accessible by Laser Absorption• Radicals: OH, CH3 …• Intermediates: CH4, C2H4, CH2O …• Products: CO, CO2, H2O …

9

Advantages of Shock Tubes• Near-Ideal Test Platform• Well-Determined Initial T & P• Clear Optical Access for Laser Diagnostics

Course Overview:Role of Lasers in Combustion Kinetics: Shock Tubes

High-Speed Camera

EC-QCL Laser(11 m)

Temperature(4.3 m)


He-Ne Laser(3.39 m)

Course Overview:Lasers and Shock Tube: Time-Histories & Kinetics

Multi-wavelength laser absorption species time-histories provide quantitative targets for model refinement and validation

Laser absorption provides high-accuracy measurements of elementary reaction rate constants

1494K, 2.15 atm300ppm heptane, =1

JetSurF 2.0H+O2 = OH+O

10

Time-Histories Rate Constant

0.3 0.5 0.7 0.91010

1011

1012

1013

OH Laser Abs. Wang et al. (2017)

H2O Laser Abs. Hong et al. (2009)

H ARAS. Pirraglia et al. (1989)

2000K

k 1 [cm

3 mol

-1s-1

]

1000/T [1/K]

1428K 1111K

OH Laser Abs. Masten et al. (1990)

Useful Texts, Supplementary Reading

11

G. Herzberg, Atomic spectra and atomic structure, 1944. G. Herzberg, Spectra of diatomic molecules, 1950. G. Herzberg, Molecular spectra and molecular structure, volume II,

Infrared and Raman Spectra of Polyatomic Molecules, 1945. G. Herzberg, Molecular spectra and molecular structure, volume III,

Electronic spectra and electronic structure of polyatomic molecules, 1966. C.N. Banwell and E.M. McCash, Fundamentals of molecular spectroscopy, 1994. S.S. Penner, Quantitative molecular spectroscopy and gas emissivities, 1959. A.C.G. Mitchell and M.W.Zemansky, Resonance radiation and excited atoms, 1971. C.H. Townes and A.L. Schawlow, Microwave spectroscopy, 1975. M. Diem, Introduction to modern vibrational spectroscopy, 1993.

W.G. Vincenti and C.H. Kruger, Physical gas dynamics, 1965. A.G. Gaydon and I.R. Hurle, The shock tube in high-temperature chemical physics, 1963.

J.B. Jeffries and K. Kohse-Hoinghaus, Applied combustion diagnostics, 2002. A.C. Eckbreth, Laser diagnostics for combustion temperature and species, 1988. W. Demtroder, Laser spectroscopy: basic concepts and instrumentation, 1996. R.W. Waynant and M.N. Ediger, Electro-optics handbook, 2000. J.T. Luxon and D.E.Parker, Industrial lasers and their applications, 1992. J.Hecht, Understanding lasers: An entry level guide, 1994. K.J.Kuhn, Laser engineering, 1998. R.K. Hanson et al., Spectroscopy and Laser Diagnostics for Gases, 2016

Lecture Schedule

12

1. Overview & IntroductionCourse Organization, Role of Quantum Mechanics,Planck's Law, Beer's Law, Boltzmann distribution

2. Diatomic Molecular SpectraRotational Spectra (Microwaves)Vibration-Rotation (Rovibrational) Spectra (Infrared)

3. Diatomic Molecular SpectraElectronic (Rovibronic) Spectra (UV, Visible)

13. Laser-Induced Fluorescence (LIF)Two-Level ModelMore Complex Models

14. Laser-Induced Fluorescence: Applications 1Diagnostic Applications (T, V, Species)PLIF for small molecules

15. Laser-Induced Fluorescence: Applications 2Diagnostic Applications & PLIF for large moleculesThe Future

7. Electronic Spectra of DiatomicsTerm Symbols, Molecular Models: Rigid Rotor, Symmetric Top, Hund's Cases, Quantitative Absorption

8. Case Studies of Molecular SpectraUltraviolet: OH

9. TDLAS, Lasers and FibersFundamentals and Applications in Aeropropulsion

4. Polyatomic Molecular SpectraRotational Spectra (Microwaves)Vibrational Bands, Rovibrational Spectra

5. Quantitative Emission/ AbsorptionSpectral absorptivity, Eqn. of Radiative TransferEinstein Coefficients/Theory, Line Strength

6. Spectral LineshapesDoppler, Natural, Collisional and Stark broadening,Voigt profiles

10. TDLAS Applications in Energy ConversionTunable Diode Laser Applications in IC EnginesCoal-Fired Combustion

11. Shock Tube TechniquesWhat is a Shock Tube?Recent Advances, ignition Delay Times

12. Shock Tube ApplicationsMulti-Species Time HistoriesElementary Reactions

Monday

Tuesday

Wednesday

Thursday

Friday

Lecture 1: Introductory Material

1. Role of Quantum Mechanics - Planck’s Law

2. Absorption and Emission3. Boltzmann Distribution4. Working Examples

13

ΔE

Eelec

Evib

Erot

Quantum Mechanics: Quantized Energy levels “Allowed” transitions

14

Eint = Eelec + Evib + Erot

1. Role of QM - Planck’s Law

How are energy levels specified?Quantum numbers for electronic, vibrational and rotational states.

We will simply accept these rules from QM}

1. Role of QM - Planck’s Law Quantum Mechanics

15

Small species, (e.g., NO, CO, CO2, and H2O), have discrete spectral features

Large molecules (e.g., HCs) have blended features

Quantized Energy States (discrete energy levels)

Discrete spectraPlanck’s Law:ΔE = Eupper (E’) – Elower (E”)

= h= hc/λ= hc Energy in wavenumbers

Energy state or level

Absorption

Emission“Allowed” transitions

Energy

ΔE

c = λ

~ 3 x 1010 cm/s Wavelength [cm]

Frequency [s-1]

Note interchangability of λ &

2. Absorption and Emission Types of spectra:

Absorption; Emission; Fluorescence; Scattering (Rayleigh, Raman)

Absorption: Governed by Beer’s Law

16

Beer-Lambert Law LSPLnTII

ijt

expexpexp

0

Number density of species j in absorbing state [molecule/cm3]

Cross section for absorption [cm2/molecule]

Path length [cm]

Absorbance

I0, ν T, P, χi,vIt

L

GasWavelength

Tran

smiss

ion

2. Absorption and Emission Components of spectra: Lines, Bands, Systems

17


r (distance between nuclei)

E(pot.)

Potential energy curve for 1 electronic state


18


Erot

Line: Single transition

λTλ

r (distance between nuclei)

E(pot.)


19


Evib


Band: Group of lines with common upper + lower vibrational levels

λTλ

Δv=vupper – vlower=1 is strongestfor rovibrational IR spectra,but Δv= 2,3, … allowed

vupper

vlowerR P Two branches,

Denoted byP&R


20


Evib


Band: Group of lines with common upper + lower vibrational levels

λTλ

Δv=1Δv=2Δv=3

Δv=1

But Δv>1 possible

vlower


21

Eelec

System: Transitions between different

electronic states Comprised of multiple bands between

two electronic states Different combinations of vupper and

vlower such that “bands” with vupper-vlower=const. appear

C3Πu

B3Πg

A3Σ+uN2(1+)


N2(2+)

Nitrogen

Example: N2 First positive SYSTEM:

B3Πg→A3Σ+u

The ground (lowest energy) state is X1Σ+

g


22

Eelec

System

Example: High-temperature air emissionspectra (560-610nm)

C3Πu

B3Πg

A3Σ+uN2(1+)

N2(2+)

Nitrogen

12→8

11→7 10→6

9→5

8→47→3

6→2

vupper=v'vlower=v" v'-v"=4



23

SystemExample: Typical emission spectra of DC discharges

UV Visible-NIR

2. Absorption and Emission

24

OH 2Σ−2Π (0,0)

CH 2Δ−2Π

CH 2Σ−2Π

CH 2Σ−2Π

NH 3Π−3Σ

In early days, spectra were recorded on film!But now we have lasers.

Components of spectra: Lines, Bands, Systems

How is Tλ (fractional transmission) measured?


25

Transmission (Tλ)

Absorption

λ

Tunable Laser Test media; Flame Iλ; Detector

1.0Δλ = Full width at half maximum

λ0 = Line center

Δλ = f(P,T)

A resolved line has shape!

Do lines have finite width/shape? Yes!

And shape is a f(T,P) an opportunity for diagnostics!

3 key elements of spectra Line positions Line strengths Line shapes


26

Covered in course

3. Boltzmann Distribution How strong is a transition?

27

Proportional to particle population in initial energy level n1

S12

Energy level 1

Energy level 2

ΔE=h

n1

Boltzmann fraction of absorber species i in level 1

QkT

g

nnF

ii

ii

exp

elecvibroti

ii QQQ

kTgQ

expPartition function

- Equilibrium distribution of molecules of a single species over its allowed quantum states.

Statistical Mechanics: Defines T!

Hence measurements of two densities ni and nj → TSince ni/nj = gi/gj exp(‐(i‐j)/kT)

TDL sensing for aero-propulsion Diode laser absorption sensors offer prospects for time-resolved, multi-

parameter, multi-location sensing for performance testing, model validation, feedback control

4. Working Example – 1

28

Exhaust(T, species, UHC, velocity, thrust)

Inlet and Isolator(velocity, mass flux, species,

shocktrain location)

Combustor(T, species, stability)

l1 l2 l3 l4 l5

Diode Lasers

Fiber Optics

Acquisition and Feedback to Actuators

l6

Sensors developed for T, V, H2O, CO2, O2, & other species Prototypes tested and validated at Stanford Several applications successful in ground test facilities Now being utilized in flight

TDL Sensing to Characterize NASA Ames ArcJet Facilities High-Enthalpy Flow for Materials and Vehicle Testing


29

High pressure gas Arc heater Nozzle

High velocity low pressure

flow for hypersonic

vehicle testing

30ft

10ft

10ft

TDL Sensing to Characterize NASA Ames ArcJet Facilities High-Enthalpy Flow for Materials and Vehicle Testing


30

High pressure gas Arc heater Nozzle

High velocity low pressure

flow for hypersonic

vehicle testing

Goals: (1) Time-resolved temperature sensing in the arc heater: O to infer T(2) Investigate spatial uniformity within heater (multi-path absorption)

Challenges: Extreme Conditions T=6000-8000K, P= 2-9 bar, I~2000A, 20 & 60 MWDifficult access (mechanical, optical, and electrical)

Cooling water

Anode Cathode

Test cabinInlet Air

TDL Sensor

Constrictor Tube

Cooling Argon

Temperature from Atomic O Absorption Measurement


31

Atomic oxygen energy diagram

777.2 nm

3P23P13P0

5P35P25P1844.6 nm

3P0,1,2

3S01 5S0

2

135.8 nm130.5 nm

Fundamental absorption transitions from O are VUV but excited O in NIR

Equilibrium population of O-atom in 5S02 extremely temperature sensitive

0.6

0.4

0.2

0.0

777.28777.24777.20777.16777.12Wavelength (nm)

-0.050.000.05

Data Fitting

Abs

orba

nce

Res

idua

ls

Atomic oxygen absorption measured in the arc heater

nO*= 6.64 x 1010 cm-3

Tpopulation= 7130±120 K

4. Working Example – 2 Arc current at 2000A, power 20MW Last 200 seconds of run arc current decreased 100A Measured temperature captures change in arc conditions

Precise temperature measurements• 18K or 0.3% standard deviation• 200ms time resolution

18 K Arc current decreased ~100A

TDL sensor provides new tool for routine monitoring of arcjet performance32

1392 nm1469 nm

2678 nm

Flow from Engine

NozzleExit

Fiber-Coupled Light to Engine

Transmitted Light Caught onto Multi-Mode Fibers

Detector for H2O Wavelengths

Detector for CO2Wavelength

Pitch Optics

Catch Optics

H2O & T

CO2

NozzleEntrance

4855 nmCOOR

Port for KistlerPressure Sensor

4. Working Example – 3Time-Resolved High-P Sensing in PDC at NPS

Pulse-detonation combustor gives time-variable P/T Time-resolved measurements monitor performance & test CFD

Assumption: Choked flow Tgives velocity

T, P, V & Xi

yields Enthalpy Flux

33


Optical sensors feasible in harsh, high pressure engine environment

34

Pulse Detonation CombustorAt Naval Post-graduate School in Monterey, CA

Pulse-detonation combustor gives time-variable P/T Time-resolved TDLAS measurements monitor performance & test CFD

Exhaust to ambient

Pulsed detonations

P

chamberthroat

Assumption: Choked flowT gives velocity

T, P, V & Xi Enthalpy Flux1469 nm1392 nm

Throat SensorsT & XH2O

(CO @ 4.6m; CO2 @ 2.7m)

35


T- Data Collected in Nozzle Throat vs CFD

T sensor performs well to >3500K, 30 atm! Data agrees well with CFD during primary blow down

36


4. Working Example – 3Time-Resolved TDLAS Yields Mass Flow

),,( sonicVPTfm

),( mixsonic TfVV

T and P give V and mass flow in choked throat as f(t) T, m, species (CO, CO2, H2O) and ideal gas law can

give enthalpy flow rate

.

37

H

m

hstag (T )

Time-resolved data provide key measures of engine performance Power (enthalpy flux) Mass flow dynamics H integrated over complete cycle for ηth

4 Consecutive Cycles

Tref = 298 K

38

4. Working Example – 3Time-Resolved TDL Yields Enthalpy Flow Rate

4. Working Example – 4Time-Resolved Sensing in HEG Shock Tunnel

39

Sensors developed for T, V, H2O, CO2, O2, & other species Prototypes tested and validated at Stanford Several successful demonstrations in ground test facilities Opportunities emerging for use in flight: sensing and control Measurements made in Mach 7.4 shock tunnel in Germany

– Diode laser absorption sensors offer prospects for time-resolved, multi-parameter, multi-location sensing for performance testing, model validation, feedback control

Exhaust(T, species, UHC, velocity, thrust)

Inlet and Isolator(velocity, mass flux, species,

shocktrain location)

Combustor(T, species, stability)

l1 l2 l3 l4 l5

Diode Lasers

Fiber Optics

Acquisition and Feedback to Actuators

l6


40

41


4. Working Example – 5First Multi-Species Sensing for Shock Tube Kinetics

Oxygen Balance:Methyl Formate Decomposition

Chemistry progress monitored by quantitative IR laser absorption

Multi-species time histories provide game-changing advantage for mechanism validation

Method accounts for nearly 100% of O-atoms

1420 K1.5 atm

Shock wave Test mixture

Detectors

Lasers

H-C-O-C-O

= __

Next: Diatomic Molecular Spectra

• Rotational and Vibrational Spectra

43

15 lecture short course at princeton university€¦ · tunable diode laser applications in ic...

Documents