scholarly journals Injector-coupled transverse instabilities in a multi-element premixed combustor

2020 ◽  
Vol 12 ◽  
pp. 175682772093283
Author(s):  
John J Philo ◽  
Rohan M Gejji ◽  
Carson D Slabaugh
Keyword(s):  
Equivalence Ratio ◽  
Pressure Fluctuations ◽  
High Amplitude ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Combustion Dynamics ◽  
Thermoacoustic Instabilities ◽  
Transverse Modes ◽  
Additional Mode ◽  
The Relationship

Combustion instabilities in a high-pressure, multi-element combustor are studied in order to understand the relationship between the chamber and injector dynamics. A linear array of seven injectors supplies premixed natural gas and air into a rectangular combustion chamber designed to promote high-frequency, transverse thermoacoustic instabilities. The effect of equivalence ratio on the combustion dynamics was investigated for two injector lengths, 62.5 and 125 mm. For all operating conditions, the 125 mm injectors promote high-amplitude instabilities of the fundamental transverse (1T) mode, which has a frequency of 1750–1850 Hz. Reducing the injector length significantly lowers the instability amplitudes for all operating conditions and, for lower equivalence ratio cases, excites an additional mode near 1550 Hz. The delineating feature controlling the growth of the instabilities in each injector configuration is the coupling with axial pressure fluctuations in the injectors that occur in response to the transverse modes in the chamber.

Fuel-Forced Flame Response of a Lean-Premixed Combustor

2011 ◽  
Author(s):  
Poravee Orawannukul ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Operating Conditions ◽  
Chemiluminescence Intensity ◽  
Combustion Dynamics ◽  
Lean Premixed ◽  
Flame Response ◽  
Rate Of Heat Release ◽  
The Relationship

The response of a swirl-stabilized flame to equivalence ratio fluctuations is experimentally investigated in a single-nozzle lean premixed combustor. Equivalence ratio fluctuations are produced using a siren device to modulate the flow rate of fuel to the injector, while the air flow rate is kept constant. The magnitude and phase of the equivalence ratio fluctuations are measured near the exit of the nozzle using an infrared absorption technique. The flame response is characterized by the fluctuation in the flame’s overall rate of heat release, which is determined from the total CH* chemiluminescence emission from the flame. The relationship between total CH* chemiluminescence intensity and the flame’s overall rate of heat release is determined from a separate calibration experiment which accounts for the nonlinear relationship between chemiluminescence intensity and equivalence ratio. Measurements of the normalized equivalence ratio fluctuation and the normalized rate of heat release fluctuation are made over a range of modulation frequencies from 200 Hz to 440 Hz, which corresponds to Strouhal numbers from 0.4 to 2.8. These measurements are used to determine the fuel-forced flame transfer function which expresses the relationship between the equivalence ratio and rate of heat release fluctuations in terms of a gain and phase as a function of frequency. In addition, phase-synchronized CH* chemiluminescence images are captured to study the dynamics of the flame response over the modulation period. These measurements are made over a range of operating conditions and the results are analyzed to identify and better understand the mechanisms whereby equivalence ratio fluctuations result in fluctuations in the flame’s overall rate of heat release. Such information is essential to guide the formulation and validation of analytical fuel-forced flame response models and hence to predict combustion dynamics in gas turbine combustors.

Experimental Investigation of Combustion Dynamics in a Turbulent Syngas Combustor

2017 ◽  
Author(s):  
Nikhil Ashokbhai Baraiya ◽  
Baladandayuthapani Nagarajan ◽  
Satynarayanan R. Chakravarthy
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Dynamic Pressure ◽  
Fuel Mixture ◽  
High Amplitude ◽  
Acoustic Oscillations ◽  
Combustion Dynamics ◽  
Dynamic Pressure Measurement ◽  
Body Location

In the present work, the proportion of carbon monoxide to hydrogen is widely varied to simulate different compositions of synthesis gas and the potential of the fuel mixture to excite combustion oscillations in a laboratory-scale turbulent bluff body combustor is investigated. The effect of parameters such as the bluff body location and equivalence ratio on the self-excited acoustic oscillations of the combustor is studied. The flame oscillations are mapped by means of simultaneous high-speed CH* and OH* chemiluminescence imaging along with dynamic pressure measurement. Mode shifts are observed as the bluff body location or the air flow Reynolds number/overall equivalence ratio are varied for different fuel compositions. It is observed that the fuel mixtures that are hydrogen-rich excite high amplitude pressure oscillations as compared to other fuel composition cases. Higher H2 content in the mixture is also capable of exciting significantly higher natural acoustic modes of the combustor so long as CO is present, but not without the latter. The interchangeability factor Wobbe Index is not entirely sufficient to understand the unsteady flame response to the chemical composition.

scholarly journals Synchronization of Thermoacoustic Modes in Sequential Combustors

2018 ◽  
Author(s):  
Giacomo Bonciolini ◽  
Nicolas Noiray
Keyword(s):  
Gas Turbines ◽  
High Amplitude ◽  
Operating Conditions ◽  
Operational Flexibility ◽  
Order Model ◽  
Thermoacoustic Instabilities ◽  
Physical Mechanisms ◽  
Sustained Oscillations ◽  
Engine Components

Sequential combustion constitutes a major technological step-change for gas turbines applications. This design provides higher operational flexibility, lower emissions and higher efficiency compared to today’s conventional architectures. Like any constant pressure combustion system, sequential combustors can undergo thermoacoustic instabilities. These instabilities potentially lead to high-amplitude acoustic limit cycles, which shorten the engine components’ lifetime and therefore reduce their reliability and availability. In case of a sequential system, the two flames are mutually coupled via acoustic and entropy waves. This additional inter-stages interaction markedly complicates the already challenging problem of thermoacoustic instabilities. As a result, new and unexplored system dynamics are possible. In this work, experimental data from our generic sequential combustor are presented. The system exhibits many different distinctive dynamics, as function of the operation parameters and of the combustor arrangement. This paper investigates a particular bifurcation, where two thermoacoustic modes synchronize their self-sustained oscillations over a range of operating conditions. A low-order model of this thermoacoustic bifurcation is proposed. This consists of two coupled stochastically driven non-linear oscillators, and is able to reproduce the peculiar dynamics associated with this synchronization phenomenon. The model aids in understanding what the physical mechanisms that play a key role in the unsteady combustor physics are. In particular, it highlights the role of entropy waves, which are a significant driver of thermoacoustic instabilities in this sequential setup. This research helps to lay the foundations for understanding the thermoacoustic instabilities in sequential combustion systems.

Dynamics and Stability Limits of Syngas Combustion in a Swirl-Stabilized Combustor

2008 ◽  
Author(s):  
Raymond L. Speth ◽  
H. Murat Altay ◽  
Duane E. Hudgins ◽  
Ahmed F. Ghoniem
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Fluid Dynamic ◽  
Flame Structure ◽  
Low Frequency ◽  
Operating Conditions ◽  
Video Data ◽  
Combustion Dynamics ◽  
Lean Blowout ◽  
Operating Modes

The combustion dynamics, stability bands and flame structure of syngas flames under different operating conditions are investigated in an atmospheric pressure swirl-stabilized combustor. Pressure measurements and high-speed video data are used to distinguish several operating modes. Increasing the equivalence ratio makes the flame more compact, and in general increases the overall sound pressure level. Very close to the lean blowout limit, a long stable flame anchored to the inner recirculation zone is observed. At higher equivalence ratios, a low frequency, low amplitude pulsing mode associated with the fluid dynamic instabilities of axial swirling flows is present. Further increasing the equivalence ratio produces unstable flames oscillating at frequencies coupled with the acoustic eigenmodes. Additionally, a second unstable mode, coupled with a lower eigen-mode of the system, is observed for flames with CO concentration higher than 50%. As the amount of hydrogen in the fuel is increased, the lean flammability limit is extended and transitions between operating regimes move to lower equivalence ratios.

Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine

1998 ◽  
Vol 120 (4) ◽  
pp. 721-726 ◽  
Author(s):  
J. R. Seume ◽  
N. Vortmeyer ◽  
W. Krause ◽  
J. Hermann ◽  
C.-C. Hantschk ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Preventive Measure ◽  
Feedback System ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Instability Control ◽  
Heavy Duty Gas Turbine

During the prototype shop tests, the Model V84.3A ring combustor gas turbine unexpectedly exhibited a noticeable “humming” caused by self-excited flame vibrations in the combustion chamber for certain operating conditions. The amplitudes of the pressure fluctuations in the combustor were unusually high when compared to the previous experience with silo combustor machines. As part of the optimization program, the humming was investigated and analyzed. To date, combustion instabilities in real, complex combustors cannot be predicted analytically during the design phase. Therefore, and as a preventive measure against future surprises by “humming,” a feedback system was developed which counteracts combustion instabilities by modulation of the fuel flow rate with rapid valves (active instability control, AIC). The AIC achieved a reduction of combustion-induced pressure amplitudes by 86 percent. The Combustion instability in the Model V84.3A gas turbine was eliminated by changes of the combustor design. Therefore, the AIC is not required for the operation of customer gas turbines.

Effects of Swirl Combination and Mixing Tube Geometry on Combustion Instabilities in a Premixed Combustor

2006 ◽  
Author(s):  
Masamichi Koyama ◽  
Hiroshi Fujiwara ◽  
Laurent Zimmer ◽  
Shigeru Tachibana
Keyword(s):  
Pressure Fluctuations ◽  
Flame Structure ◽  
Operating Conditions ◽  
Cfd Analysis ◽  
Combustion Instabilities ◽  
Mean Velocity ◽  
Piv Measurement ◽  
Pdf Analysis ◽  
Combustor Liner ◽  
Tube Geometry

In this paper, flow fields inside a premixed combustor have been investigated by CFD analysis and PIV measurement in a preheating, non-reacting condition. Four types of premixer are examined. The design of the premixer is determined by the combination of swirlers and mixing tubes. There are two variations of triple-concentric swirlers and three variations of mixing tubes. Comparisons are made among mean velocity distributions derived from CFD and PIV. PDF analysis is performed on the data from PIV to discuss the possibility of the occurrence of flashback. Combustion rig tests have been carried out also on similar condition to see combustion instabilities depending on the choice of premixers and operating conditions. Flame is directly observed from crystal windows placed on the side and downstream of the combustion chamber. A glass rod is installed on the wall of the mixing tube so as to see light emissions inside the tube, i.e. evidence of flashback. Pressure fluctuations at the combustor liner are measured in one position. The spectra of pressure fluctuations are computed to look at the possibility of combustion oscillations. Discussions are made on the relation between the global flame structure and pressure modes. Finally, proper premixer configurations to prevent combustion instabilities are proposed.

scholarly journals Mathematical Modeling of Unsteady Gas Transmission System Operating Conditions under Insufficient Loading

Energies ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1325 ◽  
Author(s):  
Vasyl Zapukhliak ◽  
Lyubomyr Poberezhny ◽  
Pavlo Maruschak ◽  
Volodymyr Grudz ◽  
Roman Stasiuk ◽  
...  
Keyword(s):  
Mathematical Modeling ◽  
Pressure Fluctuations ◽  
High Amplitude ◽  
Transmission System ◽  
Gas Pipeline ◽  
Operating Conditions ◽  
Amplitude Fluctuations ◽  
Pipeline Route ◽  
Main Gas Pipeline ◽  
System Operating

Under insufficient loading of a main gas transmission system, high-amplitude fluctuations of pressure may occur in it. A mathematical model is proposed to estimate the amplitude of pressure fluctuations in a gas pipeline along its length. It has been revealed that the shutdown of compressor stations along the gas pipeline route has a significant impact on the parameters of the unsteady transient operating conditions. The possibility of minimizing oscillation processes by disconnecting compressor stations is substantiated for the “Soyuz” main gas pipeline.

Impact of Fuel Supply Impedance on Combustion Stability of Gas Turbines

2008 ◽  
Author(s):  
Andreas Huber ◽  
Wolfgang Polifke
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Cfd Simulation ◽  
Transfer Functions ◽  
Combustion Stability ◽  
Reacting Flow ◽  
Efficient Manner ◽  
Combustion Dynamics ◽  
Thermoacoustic Instabilities ◽  
Fuel Supply

In the development of gas turbines the prevention of thermoacoustic instabilities plays an important role. The present study analyzes the influence of the acoustic impedance of the fuel supply system on combustion stability in a generic configuration representative of practical lean-premix combustors. Transient Computational Fluid Dynamics (CFD) of turbulent reacting flow and system identification (SI) are combined to obtain a description of the combustion dynamics in terms of two flame transfer functions, which describe the response of heat release rate to fluctuations of velocity and equivalence ratio, respectively. In this way, the mixing and transport of the fuel from the injector to the flame, the kinematic response of the flame to upstream flow fluctuations, and combined effects like the perturbation of flame speed and position due to equivalence ratio perturbations are all captured. The flame transfer functions obtained are combined with a network model for the system acoustics in such a way that results from a single CFD simulation can be used to investigate a wide variety of combustor and fuel supply configurations in a quantitative and very efficient manner. It is demonstrated that a change of the fuel supply impedance can significantly influence the amplitude of equivalence ratio fluctuations as well as the relative phase of the two transfer functions, and thereby provide a means for control of combustion instabilities.

Dynamic Data-Driven Design of Lean Premixed Combustors for Thermoacoustically Stable Operations

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Pritthi Chattopadhyay ◽  
Sudeepta Mondal ◽  
Chandrachur Bhattacharya ◽  
Achintya Mukhopadhyay ◽  
Asok Ray
Keyword(s):  
Experimental Data ◽  
Design Method ◽  
High Amplitude ◽  
Critical Issue ◽  
Operating Conditions ◽  
Design Parameters ◽  
System Response ◽  
Thermoacoustic Instabilities ◽  
Lean Premixed ◽  
Combustion Systems

Prediction of thermoacoustic instabilities is a critical issue for both design and operation of combustion systems. Sustained high-amplitude pressure and temperature oscillations may cause stresses in structural components of the combustor, leading to thermomechanical damage. Therefore, the design of combustion systems must take into account the dynamic characteristics of thermoacoustic instabilities in the combustor. From this perspective, there needs to be a procedure, in the design process, to recognize the operating conditions (or parameters) that could lead to such thermoacoustic instabilities. However, often the available experimental data are limited and may not provide a complete map of the stability region(s) over the entire range of operations. To address this issue, a Bayesian nonparametric method has been adopted in this paper. By making use of limited experimental data, the proposed design method determines a mapping from a set of operating conditions to that of stability regions in the combustion system. This map is designed to be capable of (i) predicting the system response of the combustor at operating conditions at which experimental data are unavailable and (ii) statistically quantifying the uncertainties in the estimated parameters. With the ensemble of information thus gained about the system response at different operating points, the key design parameters of the combustor system can be identified; such a design would be statistically significant for satisfying the system specifications. The proposed method has been validated with experimental data of pressure time-series from a laboratory-scale lean-premixed swirl-stabilized combustor apparatus.

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

2016 ◽  
Author(s):  
Richard Blümner ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner ◽  
Bernhard Ćosić
Keyword(s):  
Equivalence Ratio ◽  
Near Infrared ◽  
Fuel Injection ◽  
High Amplitude ◽  
Operating Conditions ◽  
Tunable Diode Laser ◽  
Mean Flow ◽  
Injection Point ◽  
Driving Mechanisms ◽  
Acoustic Forcing

Unsteady temporal fluctuations of the equivalence ratio in lean premixed gas turbine combustors are one of the most important driving mechanisms for thermoacoustic instabilities. In this work, high-amplitude equivalence ratio fluctuations in the mixing section of a swirl-stabilized burner are assessed for the first time. The applied non-intrusive sensor is based on fixed-wavelength modulation spectroscopy of methane at 1653 nm using a near-infrared tunable diode laser. The measurements are performed at isothermal operating conditions without the presence of a flame at 25°C and at atmospheric pressure. The equivalence ratio fluctuations are generated by acoustic forcing of the air flow while the fuel injection flow rate is kept constant. Acoustic forcing amplitudes up to 220% of the mean flow velocity are assessed. Measurements are conducted at different axial distances from the fuel injection point to study the spatio-temporal evolution of the equivalence ratio fluctuations. The results show a frequency-dependent saturation of temporal equivalence ratio fluctuations with increasing forcing amplitude, which can not be described through the available model. These results are in good agreement with preceding studies and indicate the saturation of the flame response due to a saturation of equivalence ratio fluctuations. Furthermore, a decreased attenuation of temporal mixture inhomogeneities for small forcing amplitudes is found.

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