TDL sensors: vision/fundamentals Sensing for dual-mode @ UVa Sensing for HyPulse @ ATK

1. Laser Diagnostics for Hypersonic Ground TestRonald K. Hanson and Jay B. Jeffries High Temperature Gasdynamics Laboratory Stanford University AFOSR/NASA National Center for Hypersonic Combined Cycle Propulsion, Review, June 2011 TDL sensors: vision/fundamentals Sensing for dual-mode @ UVa Sensing for HyPulse @ ATK Advanced concepts for future needs CO2, T for hydrocarbon fuel Normalized WMS to suppress noise Scanned WMS for simultaneous multi-parameter sensing

2. Vision for Laser Sensing in Hypersonic Propulsion Exhaust (T, species, UHC, velocity, thrust) Inlet and Isolator (velocity, mass flux, species, shocktrain location) Acquisition and Feedback to Actuators Combustor (T, species, stability) Fiber Optics Diode Lasers l1 l2 l3 l4 l5 l6 • Diode laser sensors offer prospects for time-resolved, multi-parameter, multi-location sensing for performance testing, model validation, feedback control • 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?

3. I t L I 0 n Doppler shifted lines Unshifted line n n1 n3 n2 Absorption Fundamentals: The Basics • TDL absorption: non-intrusive, time-resolved line-of-sight measurements • Beer-Lambert relation Multiplexed-cw-lasers Visible, NIR, extended NIR, mid-IR V absorbance • Spectral absorption coefficient • Shifts & shape of F contain information (T,P,ci) • V from Doppler shift of spectra • Wavelength-multiplexing for multi-parameters • Ratios of lines yield T • T and tn yield i(mole fraction) or niorr • Mass and momentum flux from r and V • Many-linedata for non-uniform T(x), Xi(x)… • Approaches: Direct absorption or WMS 3 3

4. Gas sample Io It Comparison of Direct Absorption and WMS (2f/1f) Baseline fit for Io Direct Absorption Injection current tuning i Lockin @1f, 2f i’ + Injection current modulation @f WMS 2f&1f 0.5 0.6 0.7 0.4 0.8 0.7 0.9 0.6 1.0 0.5 0.4 • 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 4

5. Diagnostics to Support Dual-Mode Combustion ModelingBenchmark Measurements in Combustion Tunnel @UVa Isolator Mach 2 Nozzle Combustor Tomography Extender & CARS TDL measurement planes • 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

6. 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

7. 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%

8. Review of Year 2 Measurements Y X • 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)

9. Inflow-Plane Measurements Revealed T Gradient Distribution of LOS T transverse to inflow w/11% added steam Ramp wall Fuel injection Translating LOS for TDL ≈ 0.04” From Wall Opposite Fuel Injector Inflow measurement plane Error Bars Represent ±1s from 500 samples average (0.5 seconds) • 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)

10. Diagnostics to Support HyPulse Testing @ATKBenchmark Measurements in HyPulse @ATK M5 Facility Nozzle Test Article Reflected Shock Tunnel @ ATK GASL Mach 5-25 Driver gas Air (test) gas Diaphragm

11. Planned test conditions: P = 60 kPa T = 1700 K 10-15 ms test time Diagnostics to Support HyPulse Testing @ATKBenchmark Measurements in HyPulse @ATK Inlet Flow exit Ramp fuel injection H2 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

12. 5 Beam Paths H2 Fuel Injector Ramp Optical Fibers Miniaturization of Optical System New 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 L~1”

13. 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

14. 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

15. Continued Development of New Sensor Concepts • Advanced sensor concepts to meet future needs in ground test at UVa & ATK • New sensor for CO2,T – needed for hydrocarbon fuels • Demonstration measurements in shock tubes - Complete • 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- complete • 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

16. CO2, T Sensor Using Extended-NIR Extended NIR Enables Large Increase in Sensitivity • 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 • Many candidate transitions for optimum line pair (depending on T)

17. E”= 316.77 cm-1 E”= 1936.09 cm-1 Extended-NIR Sensor for CO2, T • Strategy: Sense T by ratio of absorption by two CO2 transitions Extended-NIR • An optimum line pair (R(20) and P(70) was selected • Isolated from H2O, wide separation in E” • Validate in shock tube • Demonstrate achievable precision 1%CO2, L=10cm NIR Fiber-coupled Diodes mm

18. Shock-Tube Validation of Extended NIR CO2, T Sensor Precision Time-Resolved T from WMS-2f/1f of CO2 DFB laser Test mixture Shock wave InSb Detector Ratio of WMS-2f/1f signals for R(28) and P(20) CO2 transitions l1~2743nm l2~2752nm Validate fast, sensitive strategy for CO2, T using a shock tube • Ratio of WMS-2f signals sensitive to temperature, insensitive to pressure (1-2 atm) • Sensor provides accurate and precise time-resolved temperature

19. Shock-Tube Validation of Extended NIR CO2, T Sensor Temperature vs Time in Shock-Heated Ar/CO2 Mixtures Reflected shock arrival Reflected shock arrival Incident shock arrival 1.2 atm, 2%CO2 in Ar Tideal • 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

20. 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 Pitch Lens Modulated TDL near 1392nm Detector • Fixed l WMS-2f/1f • Ambient H2O (T=296 K, 60% RH) • L=29.5 cm, ~6% absorbance) 1392 nm, Partially Blocking Beam 1392 nm, Vibrating Pitch Lens 20

21. 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)

22. 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 ci, 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

23. Planned Measurements to Demonstrate Scanned WMS • Stanford Expansion Tube • Supersonic flow facility capable of producing a wide range of flight conditions with realistic chemistry but with limited test time Test Section Driver Section Expansion Section Driven Section Dump Tank Expansion Gas Arrival Test Gas Arrival Test Time End Test Section Pressure [kPa] Pressure trace identifies well-characterized test time Time [ms]

24. 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

25. 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