Five kHz thermometry in turbulent spray flames using chirped-probe pulse femtosecond CARS, part I: Processing and interference analysis

Thomas, Levi; Lowe, A.; Satija, Aman; Masri, Assaad R.; Lucht, Robert P.

doi:10.1016/j.combustflame.2018.11.004

Cited by 12 publications

(5 citation statements)

References 28 publications

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“…Moderate chirp in the pump and Stokes beam can also help to suppress unwanted interference from species with neighboring Raman resonances. In recent temperature measurements in liquid‐fueled flames, we encountered significant interferences in N 2 CPP fs CARS spectra when the hydrocarbon concentrations were high. These interferences resulted from the C–H stretch Raman resonances near 3,000 cm −1 .…”

Section: Resultsmentioning

confidence: 99%

Impact of moderate pump–Stokes chirp on femtosecond coherent anti‐Stokes Raman scattering spectra

Satija

Lucht

2019

J Raman Spectroscopy

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The effects of inducing moderate chirp in the pump and Stokes beams in chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CARS) spectroscopy are discussed. This is an important issue for measurements in high-pressure systems where the CARS beams must be transmitted through glass of significant thickness to reach the probe volume of interest. The effects were investigated both experimentally, by inserting disks of SF-11 glass into the pump and Stokes beam paths, and theoretically, by incorporating pulse chirp into our time-dependent density matrix (TDDM) simulations. Experimentally, we found that inducing moderate pump and Stokes chirp produced significant spectral narrowing of the nonresonant four-wave mixing contribution to the CARS signal, and this allowed us to control the resonant excitation bandwidth to eliminate interferences from neighboring species.The temperature measurement accuracy and precision were essentially unchanged with respect to the unchirped pump and Stokes case. The effect of moderate pump and Stokes chirp on the narrowing of the Raman excitation efficiency envelope was investigated by solving the full set of TDDM through direct numerical integration. The numerical efficiency of the solutions was enhanced dramatically by developing a parallel version of the TDDM code. The calculated Raman excitation efficiency profile was incorporated in our phenomenological spectral fitting codes.

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Section: Resultsmentioning

confidence: 99%

Impact of moderate pump–Stokes chirp on femtosecond coherent anti‐Stokes Raman scattering spectra

Satija

Lucht

2019

J Raman Spectroscopy

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“…Coherent Stokes Anti-Raman Spectroscopy (CARS) gives good accuracy with reasonable spatial resolution for some flames. Some new developments include the point measurement of temperature in sprays [66][67][68][69], a very novel and useful application of CARS with great potential for realistic combustors. In terms of planar techniques, two-wavelength PLIF systems have resulted in estimates of temperature for a range of flames (see, for instance, Ref.…”

Section: Experimental Diagnosticsmentioning

confidence: 99%

Turbulent Combustion Modelling and Experiments: Recent Trends and Developments

Giusti

Mastorakos

2019

Flow Turbulence Combust

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The development of better laser-based experimental methods and the fast rise in computer power has created an unprecedented shift in turbulent combustion research. The range of species and quantities measured and the advent of kHz-level planar diagnostics are now providing great insights in important phenomena and applications such as local and global extinction, pollutants, and spray combustion that were hitherto unavailable. In simulations, the shift to LES allows better representation of the turbulent flow in complex geometries, but despite the fact that the grid size is smaller than in RANS, the push towards realistic conditions and the need to include more detailed chemistry that includes very fast species and thin reaction zones emphasize the necessity of a sub-grid turbulent combustion model. The paper discusses examples from current research with experiments and modelling that focus on flame transients (self-excited oscillations, local extinction), sprays, soot emissions, and on practical applications. These demonstrate how current models are being validated by experimental data and the concerted efforts the community is taking to promote the modelling tools to industry. In addition, the various coordinated International Workshops on non-premixed, premixed, and spray flames, and on soot are discussed and some of their target flames are explored. These comprise flames that are relatively simple to describe from a fluid mechanics perspective but contain difficult-to-model combustion problems such as extinction, pollutants and multi-mode reaction zones. Recently, swirl spray flames, which are more representative of industrial devices, have been added to the target flames. Typically, good agreement is found with LES and some combustion models such as the progress variable-mixture fraction flamelet model, the Conditional Moment Closure, and the Transported PDF method, but predicting soot emissions and the condition of complete extinction in complex geometries is still elusive.

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“…13 However, such measurements do not provide information on minimal characteristic times of temperature variations in turbulent flames, which are expected to occur at microsecond timescales. Single-shot 100 kHz rate picosecond CARS gas thermometry demonstrated in an atmospheric pressure H 2 –air flame and in highly turbulent H 2 –N 2 jet-diffusion flame using pulses from a burst-mode pump laser, 14 or recent 5 kHz rate femtosecond frequency-chirped probe pulse CARS temperature measurements in turbulent spray flames of liquid ethanol and acetone, employed to provide spatially and temporally resolved temperature fields in harsh spray environments, 15 enabled to study correlations of temperatures at time intervals not less than 10 μs or 200 μs, respectively.…”

Section: Introductionmentioning

confidence: 99%

Coherent Anti-Stokes Raman Scattering Measurements of Time and Length Scales of Temperature Fluctuations in a Turbulent Flame

et al. 2023

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The ability to derive temporal and spatial scales of "instantaneous" local temperature variations in a turbulent flame by means of coherent anti-Stokes Raman scattering (CARS) spectroscopy is demonstrated, for the first time to our knowledge. The measurements employed two CARS-spectrometers with synchronized nanosecond pulse-repetitive lasers. The system was enabling to record, with a high temporal resolution of about 10 ns, series of single laser shot CARS spectra of N2 molecules from two spatially overlapped or displaced probe volumes as small as 0.03×0.03×2 mm3. The spectra were being recorded at a variable delay between two sequential shots, following each other in pairs at a repetition rate of 10 Hz. The series of 500 coupled measurements, at the delays in the range 1 μs-10 ms and the displacements up to 2.5 mm, have been performed in a few points of an open premixed methane-air flame of a laboratory burner with the time-averaged temperatures in the range 1200-1800 K. From the spectra, "instantaneous" temperatures, at the given delay and probe volume distance, have been derived. This allowed the auto-correlation coefficients of temperature fluctuations versus the delay and the displacement to be calculated. These dependences enabled to evaluate temperature correlation times and lengths under various mixture flow rates and equivalence ratios.

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Five kHz thermometry in turbulent spray flames using chirped-probe pulse femtosecond CARS, part I: Processing and interference analysis

Cited by 12 publications

References 28 publications

Impact of moderate pump–Stokes chirp on femtosecond coherent anti‐Stokes Raman scattering spectra

Impact of moderate pump–Stokes chirp on femtosecond coherent anti‐Stokes Raman scattering spectra

Turbulent Combustion Modelling and Experiments: Recent Trends and Developments

Coherent Anti-Stokes Raman Scattering Measurements of Time and Length Scales of Temperature Fluctuations in a Turbulent Flame

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