Chirped probe pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs-CARS) thermometry was performed at 5 kHz in a hydrogen jet diffusion flame with an air co-flow. Measurements were performed at different heights and radial locations within the jet diffusion flame, up to 16 nozzle exit diameters downstream (x/d = 16). The near-nozzle measurements were characterized by large, organized, buoyancy-driven instabilities that become more chaotic at the downstream locations x/d ≥ 4. The diffusion flame results highlight temperature fluctuations characteristic of the buoyancy-driven Kelvin-Helmholtz-type instability and provide new insights into the transient structure of these flames. At some measurement locations, the time-varying temperatures ranged from 300 K to nearly 2400 K. The CPP fs-CARS signal intensity is a factor of approximately 1000 times lower at 2400 K compared with 300 K. A dual-channel detection system was used to increase the dynamic range of the CARS measurements. The determination of temperature from the single shot spectra is discussed in detail. Laser and detection system parameters were determined from CPP fs-CARS spectra obtained from a near-adiabatic laminar calibration flame apparatus. The temperature precision of the system was determined from these calibration measurements and was found to be better than 2.0% at 2200 K. The influence of an instrument response function on spectral fitting parameters is systematically assessed. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
|Original language||English (US)|
|Number of pages||12|
|Journal||Journal of Raman Spectroscopy|
|State||Published - Sep 22 2015|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): ORS 1975-01
Acknowledgements: The authors would like to thank Chris Draves, Jeffrey B. Oleske, and Colin J. Ingram with Andor Technologies Inc. for allowing to borrow the Andor iXon Ultra EMCCD and spectrometer used for performing these measurements. Funding for this work was provided by the U.S. Department of Energy, Division of Chemical Sciences, Geosciences and Biosciences under grant no. DE-FG02-03ER15391 and by the King Abdullah University of Science and Technology under award number ORS 1975-01. Funding for the ultrafast laser system was provided by the Air Force Office of Scientific Research, Defense University Research Instrumentation Program, under grant no. FA9550-09-1-0387. Support for manuscript preparation was provided by the Office of Naval Research NSTAR under ID no. ILIR-4767.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.