Experimental Analysis of High-Amplitude Temporal Equivalence Ratio Oscillations in the Mixing Section of a Swirl-Stabilized Burner

Blümner, Richard; Paschereit, Christian Oliver; Oberleithner, Kilian; Ćosić, Bernhard

doi:10.1115/gt2016-56585

Cited by 4 publications

(4 citation statements)

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“…Optical access via a transparent mixing tube between the swirler and the burner front plate allows for the detection of equivalence ratio fluctuations by means of tunable diode laser absorption spectroscopy (TDLAS). 24,25 OH* intensity fluctuations are simultaneously measured in the combustion zone via a photomultiplier equipped with a 308 nm band-pass filter. Due to a modular setup of the rig, the measurement segment, where the electrodes and seven microphones are mounted, can be placed at various axial positions downstream of the flame.…”

Section: Combustion Rig Setupmentioning

confidence: 99%

Measurement and modeling of the generation and the transport of entropy waves in a model gas turbine combustor

Waßmer

Schuermans²,

Paschereit

et al. 2017

International Journal of Spray and Combustion Dynamics

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Indirect combustion noise is caused by entropy spots that are accelerated at the first turbine stage. These so-called entropy waves originate from the equivalence ratio fluctuations in the air–fuel mixture upstream of the flame. As entropy waves propagate convectively through the combustion chamber, they are subject to diffusion and dispersion. Because of the inherent difficulty of accurately measuring the burned gas temperature with sufficient temporal resolution, experimental data of entropy waves are scarce. In this work, the transfer function between equivalence ratio fluctuations and entropy fluctuations is modeled by a linearized reactor model, and the transport of entropy waves is investigated based on a convection-diffusion model. Temperature fluctuations are measured by means of a novel measurement technique at different axial positions downstream of the premixed flame, which is forced by periodic fuel injection. Experiments with various flow velocities and excitation frequencies enable model validation over a wide range of parameters.

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Section: Combustion Rig Setupmentioning

confidence: 99%

Measurement and modeling of the generation and the transport of entropy waves in a model gas turbine combustor

Waßmer

Schuermans²,

Paschereit

et al. 2017

International Journal of Spray and Combustion Dynamics

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“…The capability of a 1D transport model to account for the convection and diffusion within a 3D swirled flow, as considered in this study, has been demonstrated within the context of entropy waves and equivalence ratio fluctuations 33,38,48 . In fact, as shown by Blu¨mner et al 61 , the 1D model performs better for turbulent swirling flows than the quasi-2D model suggested by Giusti at al. 37 which accounts for mean shear dispersion but neglects turbulent diffusion.…”

Section: Transport and Mixing Of Equivalence Ratio Fluctuationsmentioning

confidence: 79%

Interaction of equivalence ratio fluctuations and flow fluctuations in acoustically forced swirl flames

Kather

Lückoff

Paschereit

et al. 2021

International Journal of Spray and Combustion Dynamics

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The generation and turbulent transport of temporal equivalence ratio fluctuations in a swirl combustor are experimentally investigated and compared to a one-dimensional transport model. These fluctuations are generated by acoustic perturbations at the fuel injector and play a crucial role in the feedback loop leading to thermoacoustic instabilities. The focus of this investigation lies on the interplay between fuel fluctuations and coherent vortical structures that are both affected by the acoustic forcing. To this end, optical diagnostics are applied inside the mixing duct and in the combustion chamber, housing a turbulent swirl flame. The flame was acoustically perturbed to obtain phase-averaged spatially resolved flow and equivalence ratio fluctuations, which allow the determination of flux-based local and global mixing transfer functions. Measurements show that the mode-conversion model that predicts the generation of equivalence ratio fluctuations at the injector holds for linear acoustic forcing amplitudes, but it fails for non-linear amplitudes. The global (radially integrated) transport of fuel fluctuations from the injector to the flame is reasonably well approximated by a one-dimensional transport model with an effective diffusivity that accounts for turbulent diffusion and dispersion. This approach however, fails to recover critical details of the mixing transfer function, which is caused by non-local interaction of flow and fuel fluctuations. This effect becomes even more pronounced for non-linear forcing amplitudes where strong coherent fluctuations induce a non-trivial frequency dependence of the mixing process. The mechanisms resolved in this study suggest that non-local interference of fuel fluctuations and coherent flow fluctuations is significant for the transport of global equivalence ratio fluctuations at linear acoustic amplitudes and crucial for non-linear amplitudes. To improve future predictions and facilitate a satisfactory modelling, a non-local, two-dimensional approach is necessary.

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“…In order to correct for these effects, a mean correction factor of 0.69 was estimated and used as a multiplier to the steady-state calibration curves presented in section "Calibration measurements" by Eqs. ( 7)- (8). The correction factor was obtained by (a) obtaining the total concentration and thus molar fractions for methane and nitrogen measured from the original steady-state calibration curves, (b) determining the correction factor required to bring all species molar fractions to add up to unity for each unsteady test case (assuming that the signal for both species are equally affected), and (c) using a mean correction factor for all unsteady test cases ( σ = 0.06).…”

Section: Unsteady Experimentsmentioning

confidence: 99%

“…However, few options are available for highfrequency (kHz) measurements. Tunable Diode Laser Absorption Spectroscopy (TDLAS) [4][5][6][7][8][9][10][11] has been used for high-frequency line of sight measurements. Fluorescence can be used for fast local measurements, if species have accessible transitions with sufficient line strength, such as the case with NO, OH, and specific species which can be accessed with continuous wave 12 or high-frequency pulsed lasers 13 .…”

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confidence: 99%

High-frequency measurement of concentration in an isothermal methane–air gas mixture using spontaneous Raman spectroscopy

Rodrigues,

Weller,

De Domenico

et al. 2023

Sci Rep

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A high-frequency (1.5 kHz) spontaneous Raman spectroscopy measurement technique is developed and applied to measure external fluctuations generated in the local concentration of an isothermal binary gas mixture of methane and air. Raman excitation is provided by a high-frequency laser at 527 nm in dual-pulsed mode. The Stokes Raman signal is collected using an EMCCD camera coupled to a high-frequency intensifier as a shutter. The emitted signal is collected over the 596–627 nm wavelength range, which allows for the simultaneous tracking of methane and nitrogen Stokes Q-branch mode signals. Calibration curves are initially obtained for each species ($${\text{CH}}_{4}$$ CH 4 and $${\mathrm{N}}_{2}$$ N 2 ) based on steady-state concentrations, and further corrected during use to detect local unsteady mixture fluctuations at gas pulsation frequencies up to 250 Hz. The main novelty is the demonstration of Raman spectroscopy for the simultaneous multispecies measurement of unsteady concentrations of gas-phase methane and air mixtures using a laser beam with a high-repetition rate, low energy per pulse, combined with a high-frequency intensifier and a single camera.

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Experimental Analysis of High-Amplitude Temporal Equivalence Ratio Oscillations in the Mixing Section of a Swirl-Stabilized Burner

Cited by 4 publications

References 0 publications

Measurement and modeling of the generation and the transport of entropy waves in a model gas turbine combustor

Measurement and modeling of the generation and the transport of entropy waves in a model gas turbine combustor

Interaction of equivalence ratio fluctuations and flow fluctuations in acoustically forced swirl flames

High-frequency measurement of concentration in an isothermal methane–air gas mixture using spontaneous Raman spectroscopy

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