Combustion instability of pilot flame in a pilot bluff body stabilized combustor

Fang, Xiao; Yang, Fujiang; Zhang, Guo

doi:10.1016/j.cja.2015.08.018

Cited by 13 publications

(4 citation statements)

References 29 publications

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“…In the past researches, the non-premixed flame was usually treated as an active control method of combustion instability in premixed flame. However, in recent studies, the self-excited combustion instability of non-premixed flame have also been observed and discussed [38,39]. For the industrial burner the air and fuel were usually organized in cross-flow jet for the objective of enhancing mixing process.…”

Section: Introductionmentioning

confidence: 99%

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Pan¹,

Ji²,

Zhu³

2023

Preprint

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The heat release response of the flame to acoustic excitation is a critical factor for understanding combustion instability. In the present work, the nonlinear heat release response of a methane-air non-premixed flame to the low frequency acoustic excitations is experimentally investigated. The flame describing function (FDF) was measured based on the overall CH* chemiluminescence intensity and the velocity fluctuations obtained by two-microphone method. The CH* chemiluminescence images and the schlieren images were analyzed to reveal the mechanism of nonlinear response. The excitation frequency ranges from 10Hz to 120Hz. The forced relative velocity fluctuation amplitude ranges from 0.10 to 0.50. The corresponding flame Strouhal number (Stf) ranges from 0.43 to 4.67. The study has shown that the flame length responds more sensitively to changes in excitation amplitude when subjected to relatively high frequency excitations. The normalized flame length (Lf/D) decreases from 3.79 to 2.37 with the increase of excitation amplitude at excitation frequency of 100Hz. The number of oscillation zones along the flame increases with increasing excitation frequency, which is consistent with the increase of the Stf. The low-pass filtering characteristic of FDF is caused by the dispersion of multiple oscillation zones, as well as the cancellation effect of the adjacent oscillation zones under relatively high frequency excitation. The cancellation effect of the positive and negative oscillation zones with various Stf is main mechanism for the local gain peak and valley. When two adjacent oscillation regions have approximate amplitudes, the overall phase-lag becomes more sensitive to changes in excitation frequency and amplitude. This sensitivity leads to nonlinear anomalous changes in the phase-lag near the frequency corresponding to the gain valley. The calculated disturbance convection time is consistent with the measured time delay in the short flame scenario. Future research is necessary to establish whether the observed agreement occurs due to the oscillation zone consistently occurring proximate to the flame's center of mass, coupled with a precise determination of the average convective velocity.

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Section: Introductionmentioning

confidence: 99%

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Pan¹,

Ji²,

Zhu³

2023

Preprint

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“…Energy conversion from heat to sound is desirable in thermoacoustic engines (TAEs) [1][2][3][4] due to its advantages in fewer moving parts and non-exotic materials compared to internal combustion engines, steam turbines, etc. Nevertheless, it is unwanted in aero-engines and land-based gas turbines [5][6][7][8] for the incurred large-amplitude thermoacoustic oscillations which would cause severe damages, such as jet panel ablation and structural vibration. The heat to sound energy conversion is generally caused by the coupling between the heat release rate pulsation and the internal acoustic field in the combustion chamber.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the stability of the Rijke-type thermoacoustic system with an axially distributed heat source

Pang,

Wang,

et al. 2023

Journal of Low Frequency Noise, Vibration and Active Control

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Due to the incurred damages to the combustors, large-amplitude self-sustained thermoacoustic oscillations are unwanted in many propulsion systems, such as liquid/solid rocket motors and aero-engines. To suppress these thermoacoustic oscillations efficiently, the mechanism of thermoacoustic instability needs to be clarified. Following the previous experimental work, the transitions to instability in a Rijke-type thermoacoustic system with an axially distributed heat source are studied numerically in this paper. The URANS numerical method is utilized and verified by means of a mesh sensitivity analysis. The influences of the axially distributed heater length, the heater location, and the mean flow velocity on the nonlinear dynamic behaviors of thermoacoustic oscillations are evaluated. To explore the corresponding mechanism behind these influences, the principle of acoustic energy conservation has been applied. The acoustic energy gains from the thermal-acoustic coupling are quantified via Rayleigh’s integral, and their phase differences are calculated by the cross-correlation function. The acoustic damping induced by the vortex dissipation is qualitatively analyzed by the characteristics of the flow fields in the Rijke tube. Finally, as the heater length, the heater location, or the mean flow velocity is varied, three mechanisms of the transitions to instability in a Rijke-type thermoacoustic system are identified.

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“…In past research, the non-premixed flame was usually treated as an active control method of combustion instability in premixed flame. However, in recent studies, the self-excited combustion instability of non-premixed flame has also been observed and discussed [38,39]. For the industrial burner, the air and fuel were usually organized in cross-flow jets to enhance the mixing process.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Nonlinear Responses of Non-Premixed Flames to Low-Frequency Acoustic Excitations

Pan

Zhu

2023

Applied Sciences

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The response of flames’ heat release to acoustic excitation is a critical factor for understanding combustion instability. In the present work, the nonlinear heat release response of a methane–air non-premixed flame to low-frequency acoustic excitations is experimentally investigated. The flame describing function (FDF) was measured based on the overall CH* chemiluminescence intensity and the velocity fluctuations obtained by the two-microphone method. The CH* chemiluminescence and schlieren images were analyzed for revealing the mechanism of nonlinear response. The excitation frequency ranges from 10 Hz to 120 Hz. The forced relative velocity fluctuation amplitude ranges from 0.10 to 0.50. The corresponding flame Strouhal number (Stf) ranges from 0.43 to 4.67. The study has shown that the flame length responds more sensitively to changes in excitation amplitude when subjected to relatively high-frequency excitations. The normalized flame length (Lf/D) decreases from 3.79 to 2.37 with the increase in excitation amplitude at an excitation frequency of 100 Hz. The number of oscillation zones along the flame increases with increasing excitation frequency, which is consistent with the increase in the Stf. The low-pass filtering characteristic of FDF is caused by the dispersion of multiple oscillation zones, as well as the cancellation effect of the adjacent oscillation zones under relatively high-frequency excitation. The main mechanism for the local gain peak and valley is the cancellation effect of positive and negative oscillation zones with various Stf. When two adjacent oscillation regions have similar amplitudes, the overall phase-lag becomes more sensitive to changes in excitation frequency and amplitude. This sensitivity leads to nonlinear anomalous changes in the phase-lag near the frequency corresponding to the gain valley. The calculated disturbance convection time is consistent with the measured time delay in the short flame scenario. Further research is required to determine whether the identified agreement is a result of the consistent occurrence of the oscillation zone in close proximity to the flame’s center of mass, in conjunction with a precise determination of the average convective velocity.

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Combustion instability of pilot flame in a pilot bluff body stabilized combustor

Cited by 13 publications

References 29 publications

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Investigation on the stability of the Rijke-type thermoacoustic system with an axially distributed heat source

Characterization of Nonlinear Responses of Non-Premixed Flames to Low-Frequency Acoustic Excitations

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