Laser Diagnostics for Hypersonic Ground TestRonald K. Hanson and Jay B. JeffriesHigh Temperature Gasdynamics LaboratoryStanford University
1.TDL sensors: vision/fundamentals
2.Sensing for dual-mode @ UVa
3.Sensing for HyPulse @ ATK
4.Advanced concepts for future needs
CO2, T for hydrocarbon fuel
Normalized WMS to suppress noise
Scanned WMS for simultaneous multi-parameter sensing
AFOSR/NASA National Center for Hypersonic Combined Cycle Propulsion, Review, June 2011
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Vision for Laser Sensing in Hypersonic Propulsion
– Diode laser 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
– Project focuses on new tools and data for hypersonic ground test• Develop, test, and validate at Stanford; targets are T, H2O, CO2, O2, V, & HCs• Apply to ground test facilities @ UVa• Transition to application in HyPulse @ ATK
– Future opportunities in other test facilities, flight?
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Absorption Fundamentals: The Basics
TDL absorption: non-intrusive, time-resolved line-of-sight measurements Beer-Lambert relation
Spectral absorption coefficient
Mass and momentum flux from r and V Many-line data for non-uniform T(x), Xi(x)… Approaches: Direct absorption or WMS
LnLkII
io
t exp)exp(
PPTTSk ii ),,()(
Wavelength-multiplexing for multi-parameters Ratios of lines yield T T and yield i (mole fraction) or ni or r
absorbance
Unshifted line
1 2 3
Doppler shifted lines
I0
It
L
Multiplexed-cw-lasersVisible, NIR, extended
NIR, mid-IRV
Shifts & shape of contain information (T,P,i) V from Doppler shift of spectra
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Comparison of Direct Absorption and WMS (2f/1f)
WMS2f&1f
Direct Absorption
Gas sample
Io It
Direct absorption: Simpler, if absorption is strong enough WMS: More sensitive especially for small signals (near zero baseline)
Ratio of two WMS-2f signals provides T (same as direct absorption) WMS with TDLs improves noise rejection (especially for non-absorption losses) Since both 2f and 1f signals are proportional to I; 2f/1f independent of optical losses
Injection current tuning
+ Injection current modulation @f
4
i’
i 0.4 0.5 0.6 0.7
0.00
0.25
0.50
0.75
Abs
orba
nce
Wavelength (relative cm-1)
Direct absorption lineshape
0.4 0.5 0.6 0.7 0.8 0.9 1.00.0
0.1
0.2
0.3 Direct Absorption Scan
Lase
r Int
ensi
ty S
igna
l
Time(ms)
Baseline fit
for Io
Lockin @1f, 2f
-0.02
0.00
0.02
0.04
WMS-2f lineshapeNor
mal
ized
2f s
igna
l
Wavelength (relative cm-1)0.4 0.5 0.6 0.7
0
2
4
6
8
WMS Scan
WM
S S
igna
l
Time (ms)0.4 0.5 0.6 0.7 0.8 0.9 1.0
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Diagnostics to Support Dual-Mode Combustion ModelingBenchmark Measurements in Combustion Tunnel @UVa
UVa facility provides steady operation Stanford TDL diagnostics will target combustor and combustor inflow
Time resolution (cw sensors allow frequency analysis) Spatial resolution
Translate LOS (vertical) for spatial resolution Monitor at multiple locations: Inflow & three downstream Targets: H2O & T for H2 fuel; CO2 & T for HC fuel
Future plans will add velocity
Mach 2 Nozzle
Isolator
CombustorTomography
Extender& CARS
TDL measurement planes
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Stanford TDLAS Timeline for UVa Tests
Measurement Campaign 1 (March 2010) UVa exit plane measurements
Measurement Campaign 2 (November 2010) 2D-resolution measurements via windows in the combustor Inflow plane characterization (with steam injection) revealed window leaks Flame-holding instabilities led to window failure preventing combustion exps
Plans for measurement campaign 3 (fall 2011) Complete 2D T and χH2O measurements in combustor
Final window design awaits combustion stability tests
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Review of Year 1: Exit Plane Results Stanford–UVa exit plane diagnostics
LOS path-averaged T and χH2O
Comparison of direct absorption and WMS WMS increased sensitivity with reduced uncertainty
Test Cases Validation of facility steam injection
Simulated vitiation with 9% and 12% H2O H2-Air Combustion w/ ϕ=.33
Results show complete combustion at tunnel exit
Mode Expected Value DA WMS
9% Steam 700-900K 860±30K 831±9K
Exit value 9.1±0.4% 9.1±0.2% 9.1±0.1%
12% Steam 700-900K 875±50K 850±6K
Exit value 12.0±0.5% 12.1±0.5% 11.5±0.1%
H2/Air Combustion 1800-2200K 1802±94K 1765±41K
f=0.33 Exit value 13% 12.8±0.5% 11.5±0.1%
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Review of Year 2 Measurements
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2D measurement system Optics on computer-controlled translation stages Measurements at multiple axial locations (Y)
Sub-mm spatial resolution on each plane (X) Measurement plan
Combustor inflow measurements with steam injection (completed Nov 2010)
Combustion measurements at 3 axial locations downstream of fuel injection
Unstable flameholding and subsequent window failure delayed these measurements (planned for fall of 2011)
X
Y
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Inflow-Plane Measurements Revealed T Gradient
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Distribution of LOS T transverse to inflow w/11% added steam
Error Bars Represent ±1 from 500 samples average (0.5 seconds)
≈ 0.04” From Wall Opposite Fuel Injector
Gradient in T likely due to cold-air leak around window on ramp wall side Observation of unstable flameholding consistent with leak
Next measurement campaign awaits successful/stable flameholding at UVaSCF (tentatively fall 2011)
Ramp wall
Inflow measurement
plane
Translating LOS for TDL
Fuel injection
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Diagnostics to Support HyPulse Testing @ATKBenchmark Measurements in HyPulse @ATK
M5 Facility Nozzle Test Article
Driver gas Air (test) gas
Reflected Shock Tunnel @ ATK GASLMach 5-25
Diaphragm
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Diagnostics to Support HyPulse Testing @ATKBenchmark Measurements in HyPulse @ATK
P = 60 kPa T = 1700 K10-15 ms test time
Planned test conditions:
Inlet
Flow exit
Ramp fuel injectionH2 fuel
Need: data for CFD validation of combustion efficiency (completeness of combustion), fuel penetration, flow characterization, etc.
Plan: Simultaneous T and χH2O at multiple lines-of-sight at several axial locations in HyPulse hydrogen fueled combustor
Challenge: High-speed (10-15ms test time), compact, multi-LOS sensor design Requires fast, sensitive sensor concepts Requires miniaturized optical components
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Miniaturization of Optical SystemNew Fiber Optics Enable Five LOS over 1” Flowpath
Five measurement LOS in each downstream plane Spatially-resolved measurements needed to validate model results Axial measurement plane locations monitored sequentially
Challenge: Optical system engineering New fiber collimators designed, fabricated, and laboratory tested
Supersonic Air Exhaust
Optical Fibers
5 Beam PathsH2 Fuel Injector Ramp
L~1”
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Two-Color TDL Sensor for H2O and T
Line selection Selected H2O features at 1338.3 nm and 1391.7 nm
Database and sensor performance measured in Stanford heated cell
Absorption measurement strategies Scanned-Wavelength Direct Absorption – 20kHz bandwidth 1f-normalized WMS-2f – 250kHz bandwidth w/ improved SNR
T sensor validation in heated cell
Heated cell
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Stanford TDLAS Timeline for ATK Tests Completed (Spring 2011):
Sensor design (line selection, measurement techniques and locations)
Validation of spectroscopic database Fiber-coupled 3 mm collimation optics designed, fabricated and tested
Remaining tasks (Summer 2011) Test article modifications @ ATK Test sensor package in Stanford shock tube or expansion tube
First HyPulse measurement campaign Planned for Fall 2011
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Continued Development of New Sensor Concepts
Advanced sensor concepts to meet future needs in ground test at UVa & ATK1. New sensor for CO2,T – needed for hydrocarbon fuels
Demonstration measurements in shock tubes - Complete2. 2/1f normalization strategy for WMS – to suppress noise from non-absorption
losses in transmitted intensity Demonstration measurements of gas T in presence of liquid aerosol-
complete3. New scanned-WMS concepts for simultaneous, multi-parameter sensing based
on refined model that accounts for simultaneous laser intensity and wavelength modulation – needed for precision velocity Demonstration measurements in Stanford expansion tube – just initiated
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Access to CO2 enabled by new DFB lasers for l >2.5 mm
The band strength near 2.7 mm is orders of magnitude stronger than NIR
CO2, T Sensor Using Extended-NIR Extended NIR Enables Large Increase in Sensitivity
Many candidate transitions for optimum line pair (depending on T)
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Extended-NIR Sensor for CO2, T
1. An optimum line pair (R(20) and P(70) was selected Isolated from H2O, wide separation in E”
2. Validate in shock tube Demonstrate achievable precision
NIR Fiber-coupled Diodes
Extended-NIR
E”=316.77 cm-1
E”=1936.09 cm-1
mm
1%CO2, L=10cm
Strategy: Sense T by ratio of absorption by two CO2 transitions
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Shock-Tube Validation of Extended NIR CO2, T Sensor Precision Time-Resolved T from WMS-2f/1f of CO2
Validate fast, sensitive strategy for CO2, T using a shock tube
Shock wave Test mixture
InSb Detector
DFB laser
2752nm
2743nmAperture
Detector
100 kHz100 kHz
T & CO2@ 40 kHz
Data Analysis
Data Acquisition
Detector
Shock Tube15 cm diameter
2752nm
2743nmAperture
Detector
100 kHz100 kHz
T & CO2@ 40 kHz
Data Analysis
Data Acquisition
Detector
Shock Tube15 cm diameter
Ratio of WMS-2f signals sensitive to temperature, insensitive to pressure (1-2 atm) Sensor provides accurate and precise time-resolved temperature
Ratio of WMS-2f/1f signals for R(28) and P(20) CO2 transitions
900 1000 1100 1200 1300 1400 1500 1600
1.5
2.0
2.5
3.0
3.5
4.0 P = 1.0 atm P = 2.0 atm
2f s
igna
l rat
io
Temperature [K]
l1~2743nml2~2752nm
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Shock-Tube Validation of Extended NIR CO2, T Sensor Temperature vs Time in Shock-Heated Ar/CO2 Mixtures
Temperature data agree well with T5 determined from ideal shock relations Temperature precision of 3 K demonstrated! Unique capability for real-time monitoring of T in reactive flows High potential for supersonic combustion applications
0 3 6 9 12-30
-20
-10
0
10
20
30
5 K
Diff
eren
ce o
f Mea
sure
d T
& T
5 [K]
Time [ms]
0 K
Reflected shock arrival
0 3 6 9 120
300
600
900
1200
0.0
0.6
1.2
1.8
2.4
Time [ms]P
ress
ure
[atm
]
Tem
pera
ture
[K]
Reflected shock arrival
Incident shock arrival
1.2 atm, 2%CO2 in Ar
Tideal
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Demonstrate normalized WMS-2f/1f No loss of signal when beam attenuated (e.g., scattering losses) No loss of signal when optical alignment is spoiled by vibration
Normalized WMS-2f/1f signals free from window fouling and particulate loading
1f-normalized WMS-2f Improves SNRAccounts for Non-Absorption Transmission Loss
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.350.00
0.03
0.06
0.09
0.12
2f/1
f Mag
nitu
de
Time (s)
0.0
0.2
0.4
0.6
1f M
agni
tude
0.00
0.02
0.04
0.06
2f/1f
1f Magnitude
2f M
agni
tude
2f Magnitude
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.00
0.03
0.06
0.09
0.12
2f/1
f Mag
nitu
de
Time (s)
0.0
0.2
0.4
0.6
1f M
agni
tude
0.00
0.02
0.04
0.06
2f/1f
1f Magnitude
2f M
agni
tude
2f Magnitude
1392 nm, Partially Blocking Beam 1392 nm, Vibrating Pitch Lens
Modulated TDL near 1392nm
Pitch LensDetector
Fixed l WMS-2f/1f Ambient H2O (T=296 K, 60% RH) L=29.5 cm, ~6% absorbance)
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1f-Normalized WMS-2f for CO2 with Scattering from ParticlesValidate in Aerosol-Laden Gases
Aerosol shock tube experiment: 2% CO2 /Ar in n-dodecane aerosol, L=10 cm P2=0.5 atm; P5=1.5 atm
2f/1f TDL sensor successfully measures T in presence of aerosol! May prove useful in silane-H2 fueled combustion
W. Ren, J.B. Jeffries, R.K. Hanson. Measurement Science and Technology 21 (2010)
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New Extension of WMS Theory for TDLs
Existing Strategy: Fixed-l WMS Well-established: improves sensitivity and noise rejection
High data rate & and facile real-time analysis Calibration-free with inclusion of laser tuning and spectroscopic models
The Opportunity: Rapid l scanning of WMS would allow simultaneous monitoring of i, T, & V 2f/1f spectra include lineshape information (T, P)
The Problem: Rapid wavelength scanning with TDLs Simultaneous variation in l and I from current-tuned TDLs distort laser WMS
The Solution: New model includes phase shifts and non-linear signal coupling Experiments underway to validate new model
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Stanford Expansion Tube Supersonic flow facility capable of producing a wide range of
flight conditions with realistic chemistry but with limited test time
Planned Measurements to Demonstrate Scanned WMS
Pressure trace identifies well-characterized test time
Test Section
Dump TankExpansion SectionDriven SectionDriver
Section
Test
Sec
tion
Pres
sure
[kPa
]
Time [ms]
Expansion Gas Arrival
Test Gas Arrival
Test Time End
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Supersonic Demonstration of Scanned WMS
Scanned WMS demonstration in Stanford expansion tube Flow model with configurable beam paths T, V, and XH2O data rate: 25 kHz
Demonstration experiments underway
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Summary and Acknowledgements Summary
Sensor and hardware for spatially-resolved gas T ready for dual mode @UVa Status: Measurement campaign planned fall 2011
Miniaturized, multi-path sensor for ATK nearly ready for shock tube/expansion tube validation
Status: Validation test underway, planned campaign fall 2011 New sensor strategies
New extended-NIR CO2, T sensor – combustion efficiency for HC fuels 1f-normalization of WMS suppresses flow-field noise – enabling technology New model for l-scanned-WMS – high speed velocity, T, XH2O sensor
Acknowledgements Collaborators: Goyne & McDaniel at UVa, Cresci & Tsai at ATK Current students: Chris Goldenstein, Ian Schulz, Wei Ren, Christopher Strand