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Smart Sensors for Advanced Combustion
Ron HansonHigh Temperature Gasdynamics Laboratory
Department of Mechanical EngineeringStanford University
GCEP presentation June 14, 2005
MotivationSensor strategySensor for IC-engine research*Sensor for gas-turbine exhaust*Sensor for T in coal-fired power plantReal-time T for combustion control*Opportunities
*see student poster
2
Why Research on Smart Sensors?Stanford has pioneered laser-based sensing for combustion systemsSmart sensors can reduce greenhouse gases in multiple ways
Expeditedevelopment of
emerging energy conversion
technologies
Real-Time Control
Internal Combustion Engines
Facilitate research on new energy conversion
technologies
Improve energy efficiency of existing
technologies
Smart Sensors
Coal-Fired Power Plants
Gas Turbine Engines
Research plan: GCEP-designed smart sensors w/collaborations for practical demonstrations
3
Sensor Strategy: Tunable Diode Laser (TDL) Absorption for Temperature and Gas Composition
Sensing Principle:Absorption of laser light by molecular transitions in combustion gases
Beer’s law: Transmission = I/Io = exp(-kνL)Absorption coefficient kν = f(temperature, pressure, gas composition)
Ratio of absorbance on two molecular transitions yields gas temperature
Measurement of absorbance with temperature yields mole fraction Use of additional lasers can yield more species (wavelength-multiplexing)
λ
Abs
orba
nce
λ2
λ1Absorbance ∝ kν
Tempk ν
2/kν
1
Ratio of peak heightyields gas temperature
4
Wavelength-Multiplexing to Extend Sensing Strategy
Wavelength-multiplexed, diode-laser sensors for simultaneous, in situ measurement of multiple quantities
T, H2O, CO, CO2 demonstrated at StanfordPotentially NO, UHC’s, fuel
Fiber-optic technology enables multiple measurement locationsFiber optics allows remote location of sensorsFiber switches allow multiple measurements paths for one sensor
Multiplexed absorption concept pioneered at Stanford
Detect light
Multiplexed lasers
Disperse transmitted
lightλ1
λ2
λ3λ4
λ1 λ3λ2 λ4
5
Smart Sensor Research at Stanford University
Opportunity:New smart sensors offer the potential for reduced GHG emissions
Enabling new innovative energy conversion conceptsExpediting development of emerging energy-conversion conceptsImproving efficiency and pollutant emissions from existing technologies
Strategy:Develop non-intrusive sensors using NIR absorption and fiber technologyTest sensor concepts with collaborations that enable access to practical engine environments, examples:
IC-engines, gas turbines, coal combustors, and new burner concepts
6
EGR(CO2) fuel
CO, NO, UHCs
Diode Lasers Fiber optics
T, H2O, fuel, EGR
Diode-Laser Sensors for IC-Engine Applications
Examples:HCCI
Ignition controlled by chemical kinetics (not spark or fuel injection)Careful control of temperature and fuel/air mixture composition needed
Hydrogen fueled IC-engines
Motivation: Reduce emissions from a major source of GHGChallenges:
IC-engines have limited optical access and time-varying T and P with soot and droplet scatteringRapid time resolution is crucial
Strategy:Develop novel sensors tailored for IC-engine research
7
Initial Sensor Design for In-cylinder T
7306.75 cm-1
7203.90 cm-1
7606 cm-1Non-resonant
3x 1Multiplexer
1200 g/mm gold grating
Detector
N2 Purged Region
aspheric lens
Single mode fiber
Pitch
5-axis stage
N2 purge tube
Engine(top view)
Catch
valves
flat windows
Multi-mode fiber
Intake humid air
Wavelength-multiplexed laser-based sensor (2 colors for H2O and 1 color off-resonance) Perform measurements in an optical research engine to prove sensing concept
8
Proof-of-Principle Tests @ University of Michigan
0.0
0.2
0.4
0.6
0.8
1.0
Crank Angle Position [deg]
intakeN
orm
aliz
ed d
etec
otr s
igna
l
7203.90 cm-1, water line 7306.75 cm-1, water line Off line
compression
intake valve occlusion
scattering from water droplet formation
360 420 480 540 600 660 7200
3
6
9
12
15
18
600 RPM motored engine
Pre
ssur
e
Initial measurement campaign shows promising resultsDemonstrated feasibility of TDL sensing in IC enginesNoise near TDC produced by excess loading of water vapor to intake air
Potential for significant improvements w/2nd generation sensor design: e.g. line selection to optimize T sensitivity at high P, improved optical engineering to suppress vibration noise,…Sensor can be tailored to investigate various engine operation modes and cycles
e.g. HCCI, Compression Ignition, Spark Ignition, High-EGR, Supercharged, …
540 570 600 630 660 690 720
300
400
500
600
700
800 600 RPM motored engineXH2O
= 0.03
Compression stroke
Tem
pera
ture
[K]
Crank Angle Position [deg]
Measured
Quartz Cylinder Temperature
droplet scattering
9
Tests Planned for 2nd Generation T Sensorin Optical Research Engines @ Sandia National Laboratory
Two state-of-the-art optical engine facilities for sensor validation and testUtilize TDL-based T and XH2O sensor to investigate HCCI engine operationSensor goal: Facilitate development of HCCI engines to reduce GHG emissions
Dual-Engine HCCI LabPI: John Dec
Automotive HCCI LabPI: Richard Steeper
10
Opportunities for Future IC Engine Measurements
Extend T and P sensing ranges to monitor fired-engine operation
Investigate other species (CO, CO2, fuel, UHCs, NO)
Measure non-uniformities in engine using new TDL concepts
Utilize advanced TDL schemes for improved SNR (e.g. WMS)
Monitor at multiple locations: intake, exhaust, in-cylinder
Extend to Diesel engines
Impact: Unique TDL sensors will facilitate development and control of new concept IC-engines
For details see student poster (Mattison)
11
Gas Temperature Sensor for Stationary Gas Turbine ExhaustMotivation:
Innovative in situ exhaust sensors could provide engine health data needed to minimize environmental impact
Optimizing maintenance schedule for planned load managementOptimizing burners for minimal pollutants and GHG emissions
2x1 Multiplexer
Gas TurbineExhaust Casing(cross section)
Diode LaserController
InGaAsdetectorDSP
Laptopcomputer
High-temperaturesingle-modeoptical fiber
High-temperaturemulti-modeoptical fiber
Instrumentation Shed
Laser 1
Laser 2
Rotor
Research Plan:Two-color T sensor designed and tested at SUDemonstrated in exhaust of a 20MW power generator (collaboration with GE Research Center):
For details see student poster (Liu)Readily extended to multiple paths (tomography)
12
Gas Temperature Sensor for Coal-Fired Power Plants
Strategy:Sensors developed at Stanford tested in coal combustors in Colorado and TVA with collaboration with Zolo Technologies:
Provides fiber technology to enable practical implementationProvides access to power plants to test measurement concepts
Motivation:In situ sensors can improve combustion efficiency
Efficiency increase of 1% reduces GHG by 1% and saves $1M/year in fuel (coal) costs for a 600 MW boilerPath-integrated sensing allows optimization of over-fire-air addition
Sensors can optimize maintenanceIdentify burner malfunction from temperature profile
Challenges:Long path, nearly opaque, vibration and thermal movement
13
T Sensor Design via H2O AbsorptionT sensor based on water vapor absorption H2O absorption is strong in combustion gases
4-12% H2O present in combustion products (depends on coal H2O content )Nearly 500,000 lines in HITRAN between 1 and 2 μm
10-4
10-3
10-2
10-1
100
101
S [cm
-2
/atm
]
2.01.81.61.41.21.0Wavelength [μm]
ν2+2ν32ν1+ν2ν1+ν2+ν3
2ν3ν1+ν32ν1
ν2+ν3ν1+ν2
10-4
10-3
10-2
10-1
100
101
S [cm
-2
/atm
]
2.01.81.61.41.21.0Wavelength [μm]
ν2+2ν32ν1+ν2ν1+ν2+ν3
2ν3ν1+ν32ν1
ν2+ν3ν1+ν2
ν2+ν3ν1+ν2
Use Stanford design rules to choose multiple water lines for optimal sensor performance in the harsh environment of the coal combustorExploit 1250-1650 nm region with available telecommunications lasers and optical fiber technology
14
T Sensor Design: H2O Line Selection
Coal combustor has long path lengths (10-20 m) and poor transmissionTherefore need weak lines (database is not accurate or complete)
Strategy: Choose 9 suitable lines, scanned by 3 diode lasersNeed to determine spectroscopic parameters in lab to enable measurements
Comparison of HITRAN and SU dataLines selected for sensor (A-D)
Note: A, C missing from HITRAN
-1.0 -0.5 0.0 0.5 1.00.0
0.1
0.2
0.3
0.4
Abs
orba
nce
Relative wavenumber [cm-1]
Pure H2O, 1095K, 20.75 Torr, L=381 cm measured HITRAN 2004
A
BC
D
Accurate diode laser sensing of temperature requires laboratory measurements of fundamental spectroscopic data
Example of need for accurate spectroscopic data
15
Laboratory Experiments for Quantitative Spectral Data
NEL DFBDiode laser
computer
Detector 1
N2-purged Area
vacuum vacuumH2OThermocouples
30”50”
3-zone furnace
Detector 2
Etalon
Collimating lens
Measure line strength versus T to verify E” assignment and provide quantitative S(T), line broadening, and line shift dataUse multi-pass geometry for accurate measurement of weak linesApproach yields substantial improvements to current spectral database
16
Linestrength Measurements: Example for Line A
Measure absorbance for known H2O in heated cell for S(T)Fit to confirm E” assignment and find S(T0)
500 1000 1500 2000 2500 30000.0000
0.0005
0.0010
0.0015
Line
stre
ngth
[sm
-2/a
tm]
Temperature [K]
Line A measured fitted: E"=3655.53cm-1, S(T0)=6.93 E-8 E"=3655.53cm-1, S(T0) +/- 5%
( ) ( ) ( )( )⎥⎦
⎤⎢⎣
⎡−−−−
×⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−−=
00
00 "exp1
"exp111"exp)(
)(kThcEkThcE
TTkhcE
TQTQ
TSTS
End result: First determination of line strength for this previously unknown hot line
17
Example Results w/ Nine-Line H2O T Sensor: 220MW Plant
Detect light w/ detector/laser
Multiplexed lasers
Disperse transmitted
light
D1 D3D2
Multiplex 3 lasers and scan 9 H2O linesValmont coal-fired 220MW power-plant in Colorado (dry coal)Boltzmann plot fits one temperature(1500K) with XH2O ~ 5.9%Sensor confirms uniform T in combustor, i.e. well-balanced burners with proper over-fire-air flow
1000 2000 3000 4000 5000 6000
4
6
8
10
12
14
16
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20
22
ln(A
rea i/S
0 i)
E" [cm-1]
measured linear fit: T=1485+/-80 K (5.4%)
A
B
C
D
E
FG
H
I
Laser 1
Laser 2
Laser 3
Example Results w/ 2nd Generation Sensor: 280MW Plant (T vs Time w/Multiple Paths)
TVA: coal-fired power plant280 MW, tangentially firedFiber-coupled sensor (multiple locations)Coarse tomography (4X2) of T field
200 250 300 350 400 450 5001250
1300
1350
1400
1450
1500
1550
12.5
13.0
13.5
14.0
14.5
15.0
15.5
H2O
(%)
Tem
pera
ture
[K]
Time [minutes]
Temperature
H2O (%)
Path5 (SOFA), 10-kHz scan rate, 10-s averaging
2-D temperature map @ 10mSecondary-over-fire air location(Max: 1528K, Min: 1425K)
Thundershowers begin
9.7 m
7.7
m
Note sensitivity of sensor to intake air/fuel conditionsSuccess achieved has led to a proposal for a permanent sensor installation to improve combustor efficiency and reduce GHG emissions
19
Demonstrate Use of T Sensor for Combustion Control
Motivation:Reducing the fuel-air equivalence ratio can improve combustor emissions and combustion efficiencyBut fuel lean systems are notoriously unstableTDL sensors offer the potential for control strategies to extend lean operating limits
Fiber-Coupled Diode Laser
Filtered Detector
Collimator
Jet-A fueled
Challenges:Poor optical access, high noise/vibration, time-varying transmission, and need for high-speed, real-time sensor
Strategy:Develop fast, real-time (2kHz) gas temperature measurement for combustion control
Novel wavelength modulation design to enable real-time data analysisTest Stanford sensors in practical swirl-stabilized burner
Triple annular swirl-stabilized burner at Stanford simulates next-generation gas turbine fuel nozzles
20
HardwareLock-in
Scanned-Wavelength Modulation with 2f Detection:Facilitates Real-Time T Measurement
Use of 2f simplifies data analysis ==> increases measurement bandwidthDevelopment of 2f method for T requires extension of 2f theory
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4
3
2
1
0
Det
ecto
r si
gnal
(Vol
ts)
1.00.80.60.40.20.0Sampling time (ms)
Laser Scan with Modulation
0.06
0.04
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0.00
-0.02
-0.04
2f S
igna
l (ar
b. u
nits
)1.00.80.60.40.20.0
Sampling time (ms)
2f Line Shape
Ramp
Measurement path
+
Detector signals to lock-in
Diode laser Controller
Computer
Functiongenerator
Diode Laser
Collimator
Modulate at f
Lock-in amplifier
Reference signal
Functiongenerator
Harmonic Signal
21
The transmission coefficient can be written in terms of the modulation and expanded in a Fourier series: The interpretation of 2f signals is simplified for weak absorbances (kvL << 1) :
The 2f Fourier component simplifies as:
The ratio of 2f peak heights is used to determine temperature :
WMS Sensor for Real-Time T@ 2kHz: Relevant Absorption Theory
))2cos(( fta πντ ⋅+ ∑∞
=0
)2cos(),(k
k ftkaH πν=
2f P
eak
Rat
io
Temp
2f S
igna
l
Wavelength
Ratio of 2f peak heightyields gas temperatureλ1
λ2 2f peak height
θθθνφπ
νπ
πda
LpSaH i ⋅⋅+
⋅⋅−= ∫
+
−2cos)cos(),(2
112 1
2 22 2
( cos )cos 2( )( ) ( cos )cos 2
a dH SSH a d
π
ππ
π
φ ν θ θ θνν φ ν θ θ θ
+
−+
−
+ ⋅ ⋅=
+ ⋅ ⋅
∫∫
( ) ( ) ( ) LPXXTPTSLkLk OHOH 22,,11exp φτ νν −=−≈−=
Impact: New 2f T-sensor should have broad impact on energy conversion research and technology
22
Example Results: Sensor Reveals Thermal Acoustic Instability
First application of TDL sensing in a spray flameQuartz duct used to generate natural flame instabilityPower spectrum yields the Trms at the instabilities near 350 and 700 HzScanned-wavelength 2f sensor shows promise for control applications
Fiber-Coupled Diode Laser
Collimator
Filtered Detector
FilteredPMT
CH* chemiluminescence's signal
Microphone
• 2kHz real-time T measurement in unstable ethanol/air flame
10080604020
0
Trm
s[K
]
10008006004002000Frequency [Hz]
3.0x103
2.5
2.0
1.51.0
T [K
]
0.50.40.30.20.10.0Time [s]
FFT
2000 Hz Real-time
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Example Results: First TDL Sensor Control of Swirl-Stabilized Flame
First application of TDL sensing to stabilize a spray flameNaturally unstable flame from finite length flame ductActive control of air flow suppresses instabilityResults suggest that the T sensor has good potential as a localized control variable, and could be combined with species concentration sensor
For details see student poster (Li)
0.30
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0.05
0.00
Po
wer
Sp
ect
rum
[a.
u. rm
s2]
8006004002000Frequency [Hz]
Control On (10∼10.5 s)
2f Sensor0.30
0.25
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0.15
0.10
0.05
0.00
Po
wer
Sp
ect
rum
[a.
u. rm
s2]
8006004002000Frequency [Hz]
Control Off (9.5∼10 s)
2f Sensor
Control Off Control On
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Summary of Key Accomplishments – Future Opportunities
Key Accomplishments:Innovation and design of unique in-situ sensors based on fiber-coupled near-infrared diode lasersContributions to the NIR H2O spectral databaseSensors demonstrated in practical environment with help from collaboratorsSensors can reduce GHG emissions in multiple ways:
Improve fuel efficiencyFacilitate R&D of new energy conversion conceptsReduce combustion-generated pollutants
Future Opportunities:Extend sensing concept to mid-infrared for fuels and trace gasesDevelop sensors for applications to other energy conversion schemes; e.g. fuel cellsContinue Stanford’s unique role of sensor innovation, engineering, and transfer to practical combustion systems
25
Acknowledgements
Students: Dan Mattison, Xiang Liu, Hejie Li, and Xin Zhou
Staff: Dr. Dave Davidson and Dr. Jay Jeffries
Collaborators who enabled sensor tests in practical combustion systemsVolker Sick, University of MichiganDennis Seibers, John Dec, and Dick Steeper, Sandia National LaboratoryMark Woodmansee, GE Global Research CenterAndy Sappey, Zolo TechnologyEphraim Gutmark, University of Cincinnati with thanks to GE Aircraft Engines (fuel spray concept) and Goodrich Corporation (fuel injector)