Photophysical effects on laser induced grating spectroscopy of toluene and acetone

Williams, B. A. O.; Ewart, Paul

doi:10.1016/j.cplett.2012.07.052

“…High frequency CARS, however, relies on expensive set-ups, high power lasers and complicated data analysis [30]. LIGS requires a significantly simpler set-up and data analysis than CARS, as has been demonstrated in reacting and non reacting flows to measure gas properties such as temperature, pressure, velocity and species concentration [31][32][33][34][35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

A generalised model for acoustic and entropic transfer function of nozzles with losses

Domenico

¹

,

Rolland

²

,

Hochgreb

³

2019

Journal of Sound and Vibration

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Temperature and composition spots in a turbulent flow are detected and time-resolved using Laser Induced Thermal Grating Spectroscopy (LITGS). A 355 nm wavelength PIV laser is operated at 0.5-1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In a open laminar jet, a feasibility study shows that small (3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, travelling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access.

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“…Secondly, this arrangement produces a collimated signal beam that can be propagated to the detector efficiently without requiring a re-collimating lens near the interaction region where it is prone to collect scattered light that reduces the signal-to-noise ratio. [39]. The continuous probe beam is produced by a CNI MLL-III-671 diodepumped solid state laser (λ = 671 nm, power = 300 mW, diameter ∼ 1 mm) and sampled via a 99:1 splitter.…”

Section: Optical Layoutmentioning

confidence: 99%

“…High frequency CARS, however, relies on expensive set-ups, high power lasers and complicated data analysis [30]. LIGS requires a significantly simpler set-up and data analysis than CARS, as has been demonstrated in reacting and non reacting flows to measure gas properties such as temperature, pressure, velocity and species concentration [31][32][33][34][35][36][37][38][39].Much of the previous literature has covered LIGS measurements using low repetition rate, high power lasers. Recent experiments have demonstrated LITGS (Laser Induced Thermal Grating Spectroscopy) at frequencies up to 10 kHz [40] at 532 nm using NO 2 as an absorber gas.…”

mentioning

confidence: 99%

High Frequency Measurement of Temperature and Composition Spots With LITGS

Domenico

¹

,

Shah

²

,

Fan

³

et al. 2018

Journal of Engineering for Gas Turbines and Power

Self Cite

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Temperature and composition spots in a turbulent flow are detected and time-resolved using Laser Induced Thermal Grating Spectroscopy (LITGS). A 355 nm wavelength PIV laser is operated at 0.5 -1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In a open laminar jet, a feasibility study shows that small ( 3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, travelling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access. NOMENCLATUREc Speed of sound [m/s] c p Specific heat capacity at constant pressure [J/kg/K] c p Specific heat capacity at constant pressure [J/mol/K] f LITGS oscillation frequency [Hz] m Mass flow rate [slpm-kg/s] p Pressure [P] p atm Atmospheric pressure [Pa] p s Partial pressure of the saturated vapour [Pa] Q Power [W] R Gas constant [J/mol/K] t Beam thickness [mm] T Temperature [K] X Molar concentration [-] X s Molar concentration in saturated conditions [-] W Bulk molecular weight [g/mole] δ Dilution ratio [-] γ Ratio of specific heat [-] λ Laser wavelength [m] Λ Grating spacing [m] ρ Density [kg/m 3 ] σ f Standard deviation of the LITGS frequency [Hz] θ Crossing angle (pump beams) [rad] θ B Bragg angle [rad] τ Oscillation period [s] 1 De Domenico GTP-18-1380 ASME © https://creativecommons.org/licenses/by/4.0/ ∆T TC Temperature increase measured with thermocouple ∆T LIT GS Temperature increase measured with LITGS [ ] ab Property of the air + biacetyl gas mixture [-] [ ] a Property the air-only flow [-] [ ] i Property secondary gas (CO 2 , Ar, He) [-] [ ] 0 Property of the reference point [-] INTRODUCTIONCombustion noise has become a major research interest within the aerospace community. Stricter emission regulations forced the introduction of lean premixed prevaporised combustors, which produce less NOx but burn more unsteadily, generating more noise and creating the potential for combustion instabilities. Fluctuations in the heat release rate of a flame produce isentropic pressure waves (direct noise), as well as pockets of different temperature, density and composition. Once produced, these entropy and composition spots are advected with the mean flow until they reach the first stage of the gas turbine, where they are accelerated, generating sound waves (indirect noise) [1][2][3][4][5][6][7]. These acoustic waves are partially reflected upstream in the combustor, where they may couple with the combustor acoustics, triggering a low frequency combustion instability often called...

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“…Acetone or toluene has frequently been used as absorbers in LIGS experiments at 266 nm. [33][34][35] However, this method is limited to measurements before combustion since the tracers are consumed during combustion. For measurements in the burned zone of flames, absorption lines of nitric oxide (NO) around 226 nm [36] or water around 3 μm [37,38] that are naturally present in flames have been utilized.…”

Section: Introductionmentioning

confidence: 99%

Investigation of laser‐induced grating spectroscopy of O₂ for accurate temperature measurements towards applications in harsh environments

Hot

¹

,

Sahlberg

²

,

Aldén

³

et al. 2021

J Raman Spectroscopy

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We present an in-depth investigation of laser-induced grating spectroscopy (LIGS) for temperature measurements in practical applications using a narrow-band dye laser with 760 nm wavelength and a pulse duration of 8 ns as the source for the pump beams creating the laser-induced grating. The pump laser wavelength was set to be either resonant with the R Q 5 ð Þ transition from the b 1 Σ + g υ 0 = 0 ð Þ X 3 Σ − g υ 00 = 0 ð Þ band of O 2 for generation of thermal LIGS or nonresonant for generation of purely electrostrictive LIGS. Signals were generated in ambient air as well as in high-pressure or high-temperature dry air mixtures. Pump laser irradiances up to 11 GW/cm 2 were used, which resulted in strong electrostrictive contribution to the overall LIGS signals at atmospheric pressure, with a low thermal contribution due to the weak absorption by the singlet O 2 b 1 Σ + g , v 0 = 0. The advantage and disadvantage of thermal or electrostrictive LIGS for temperature measurements are discussed, as well as potential applications in high-pressure environments. Furthermore, the precision of the temperature measurement is discussed by comparing different analysis methods.

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Photophysical effects on laser induced grating spectroscopy of toluene and acetone

Cited by 6 publications

References 18 publications

A generalised model for acoustic and entropic transfer function of nozzles with losses

A generalised model for acoustic and entropic transfer function of nozzles with losses

High Frequency Measurement of Temperature and Composition Spots With LITGS

Investigation of laser‐induced grating spectroscopy of O₂ for accurate temperature measurements towards applications in harsh environments

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Photophysical effects on laser induced grating spectroscopy of toluene and acetone

Cited by 6 publications

References 18 publications

A generalised model for acoustic and entropic transfer function of nozzles with losses

A generalised model for acoustic and entropic transfer function of nozzles with losses

High Frequency Measurement of Temperature and Composition Spots With LITGS

Investigation of laser‐induced grating spectroscopy of O2 for accurate temperature measurements towards applications in harsh environments

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Product

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Investigation of laser‐induced grating spectroscopy of O₂ for accurate temperature measurements towards applications in harsh environments