1. CHIRPED PROBE PULSE FEMTOSECOND COHERENT ANTI- STOKES RAMAN SCATTERING FOR TURBULENT COMBUSTION DIAGNOSTICS 69 th International Symposium on Molecular Spectroscopy June 16, 2014 Claresta Dennis and Robert Lucht Department of Mechanical Engineering, Purdue University West Lafayette, IN

2. INTRODUCTION TURBULENT COMBUSTION DIAGNOSTICS  Non-intrusive laser based spectroscopy methods are ideal N. Oshima, T. Tominaga, K. Saito, Proc. Symposium on Power Ener. Engr., 2008; 6. Mitsubishi 1700 Class Gas Turbine John Zink Ultra Low Emission Burner John Zink Hamworthy Combustion http://www.johnzink.com/applications/ethyle ne-applications/

3. INTRODUCTION COHERENT ANTI-STOKES RAMAN SCATTERING

4. INTRODUCTION CHIRPED PROBE PULSE FEMTOSECOND CARS

5. EXPERIMENTAL SYSTEM Ti:Sapphire Laser Output  10.2 W average power  60 fs duration laser pulses  800 nm center wavelength  ~400 cm -1 bandwidth

6. CALIBRATION FLAME  Hencken burner – stable, uniform, near-adiabatic H 2 /air flame  25 mm square fine honeycomb structure with protruding hypodermic needles  Volumetric flow rates of fuel and oxidizer controlled to produced specific flame temperatures http://www-personal.umich.edu/~mswool/facilities.htm Frequency / cm -1

7. SPECTRAL MODELING Hencken burner spectrum Single Hencken burner spectrum Laser Parameters Genetic Algorithm Based Spectral Fitting Code Laser Parameters Laser Beam Power Spectra Single Shot Genetic Algorithm Based Spectral Fitting Code Single Shot Genetic Algorithm Based Spectral Fitting Code Vibrational N 2 CPP fs-CARS temperature measurements at 5 kHz Hencken burner spectrum Fix flame temperature 2000 shots averaged and background subtracted Temperature, scaling factors floated Hencken burner spectrum Accuracy of temperature measurements is affected by the accuracy of calculated laser parameters and accuracy of the reference flame temperature

8. PRECISION AND ACCURACY  Histograms from 2000 single laser shot measurements in Hencken burner  Typical values: precision better than 2% accuracy ~ 3%  Precision and accuracy improve increasing temperature

9. RESULTS JET DIFFUSION FLAME  Jet nozzle exit diameter = 5 mm  Co-flow exit diameter = 160 mm  9 SLPM (7.7 m/s) of hydrogen  180 SLPM (0.15 m/s) of laboratory shop-air

10. RESULTS JET DIFFUSION FLAME

11. RESULTS DLR GTMC DUAL SWIRL BURNER  Operated at “Flame V” condition  Global Equivalence Ratio = 0.65  Adiabatic Flame Temperature = 1660 K  Many previous studies: PLIF of OH, CH and H 2 CO, laser Doppler anemometry (LDA), OH* chemiluminescence imaging, Raman scattering, two-line OH PLIF thermometry, and stereoscopic PIV

12. RESULTS DLR GTMC DUAL SWIRL BURNER

13. RESULTS DLR GTMC DUAL SWIRL BURNER  Performed PSD analysis to compare with previous thermo-acoustic measurements  25,000 single-laser-shot fs-CARS measurements used  Observed power spectrum peaks at 176, 308, 485, 796-805 Hz  308 Hz = frequency of dominant longitudinal thermo-acoustic pulsation  485 Hz = precessing vortex core Agrees with previous studies where PVC frequency occurred at 515 Hz I. Boxx, M. Stöhr, C. Carter, W. Meier, Combust. Flame, 2010; 157, 1510-1525.

14. CONCLUSIONS  Successfully demonstrated CPP fs-CARS in turbulent combustor of practical interest  Excellent spatial resolution and improved accuracy/precision over ns-CARS measurements Future work:  Improve the technique’s dynamic range by splitting the CARS signal into two detector channels (two spectrometers, two EMCCD cameras)

15. ACKNOWLEDGMENTS  Dr. Isaac Boxx and Dr. Wolfgang Meier from DLR Sttutgart  Devashish Bangar, Dr. Carson Slabaugh, Dr. Aman Satija  Funding provided by US Department of Energy, Division of Chemical Sciences, Geosciences, and Biosciences  Ultrafast laser system purchased with funding from an AFOSR DURIP grant  Naval Air Warfare Center Graduate Research Fellowship

16. QUESTIONS?

17. BACKUP *T. Lang and M. Motzkus, J. Opt. Soc. Am. B, 2002, 19.  First demonstrated by Lang and Motzkus*  Allows single laser shot measurements D. R. Richardson, R. P. Lucht, W. D. Kulatilaka, S. Roy, J. R. Gord, Appl. Phys. B, 2011, 104.

18. BACKUP CHIRPED PROBE PULSE FEMTOSECOND COHERENT ANTI-STOKES RAMAN SCATTERING FOR TURBULENT COMBUSTION DIAGNOSTICS J. R. Gord, T. R. Meyer, S. Roy, Ann. Rev. Anal. Chem. 2008 ; 1. Nanosecond laser-based Raman excitation Femtosecond laser-based Raman excitation  Ultrafast lasers are inherently broadband, create stronger Raman coherence in medium  Measurements are acquired over timescales faster than molecular collisions occur  Solid state laser, excellent spatial mode, no shot-to-shot fluctuations in laser spectrum