Comparison of Equivalence Ratio Transients on Combustion Instability in Single-Nozzle and Multi-Nozzle Combustors

2018 ◽  
Author(s):  
Xiaoling Chen ◽  
Wyatt Culler ◽  
Stephen Peluso ◽  
Domenic Santavicca ◽  
Jacqueline O’Connor
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Combustion Instability ◽  
Driving Mechanism ◽  
Gas Turbine Combustor ◽  
Rate Distribution ◽  
Ratio Change

Low-emissions gas turbine combustion, achieved through the use of lean, premixed fueling strategies, is susceptible to combustion instability. The driving mechanism for this instability arises from fluctuations of pressure, fuel/air flow rate, and heat release rate. If these fluctuations are relatively in-phase, the combustion system will evolve to a self-excited state. The self-excited instability frequency and amplitude depend mainly on the operating condition and the geometry of the combustor. In this study, we consider the onset and decay of self-excited instabilities, resulting from transients in fuel/air ratio, in both single-nozzle and multi-nozzle combustors. In particular, we examine the differences in the instability onset and decay processes between these two flame configurations, as most gas turbine combustors have multiple nozzles, but most gas turbine combustor experiments utilize a single-nozzle. A nonlinear logistic regression analysis is applied to study the timescales of the decay and onset transients. Variations in the equivalence ratio change the heat release rate distribution inside the combustor, which is captured using chemiluminescence imaging. The normalized Rayleigh index, which shows the spatial distribution of the instability driving, is calculated to analyze the driving strength in different regions of the flame. Comparisons between the single- and multi-nozzle flame transients, including both center and outer flames for the multi-nozzle combustor, suggest that both confinement from the wall and flame-flame interaction are crucial to determining flame dynamics as the equivalence ratio transient changes the heat release rate distribution near corner recirculation zone and flame shear layers.

4D Measurements and Analysis of Heat Release Rate in a Model Gas Turbine Combustor

2020 ◽  
Author(s):  
Rongxiao Dong ◽  
Qingchun Lei ◽  
Yeqing Chi ◽  
Qun Zhang ◽  
Wei Fan
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Surface Area ◽  
Heat Release Rate ◽  
Release Rate ◽  
Flame Surface ◽  
Global Instability ◽  
Gas Turbine Combustor ◽  
Model Gas Turbine Combustor ◽  
Edge Contours

Abstract Time-resolved volumetric measurements (4D measurements) were performed to study the heat release rate characteristics in a model gas turbine combustor at 10 kHz. For this purpose, a high-speed camera combined with an image intensifier and a set of customized fiber probes were employed to continuously capture the CH* chemiluminescence signals from nine different viewing angles. Based on the measurements, the computed tomography program was performed to reconstruct the shot-to-shot 3D distributions of the CH* signals. Specific focuses have been made to demonstrate the capabilities of the current tomographic technique in applications of a realistic combustor, in which the full optical access was usually not available for every viewing angle. The results showed that the 3D reconstruction can successfully retrieval the flame edge contours rather than the signal intensity. The flame surface area was then calculated based on the reconstructed flame edge contours and used to infer the heat release rate. The fluctuation of global/local flame surface area indicated that there existed distinct difference between the global instability and local instabilities at various locations in the non-symmetric combustor. The global instability appears to be an integration of those local instabilities.

Open Loop Active Control of Combustion Noise in Gas Turbine Combustor

2015 ◽  
Author(s):  
Srihari Dinesh Kumar Juvva ◽  
Sathesh Mariappan ◽  
Abhijit Kushari
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Active Control ◽  
Heat Release Rate ◽  
Release Rate ◽  
Sound Pressure ◽  
Open Loop ◽  
Combustion Noise ◽  
Gas Turbine Combustor ◽  
Direct Combustion

The presented study is on a laboratory scaled industrial gas turbine combustor of intensity 25MW/m3 atm, where an open loop active control technique is investigated. Combustion noise is classified as direct and in-direct combustion noise. The present study is focused on the investigation of direct combustion noise. It occurs when the volume of the gas fluctuates due to the fluctuations in heat release rate, caused perhaps due to flow turbulence. This results in sound waves, which propagate outside the boundary of the flame. The radiated acoustic waves are reflected from the boundaries of the combustion chamber, perturbing the fuel flow rate and hence the spray characteristics. This eventually leads to perturbation in the heat release rate and thus a feedback loop is established. At certain conditions, if the unsteady heat release rate drives the acoustic oscillations, satisfying Rayleigh criterion, pressure oscillations grow leading to discrete tonal sound and this phenomena is termed as combustion instability. Experiments are performed in a scaled down swirl stabilized liquid fueled gas turbine combustor, where a new scheme for open-loop control of combustion noise using periodic fuel injection is employed without drastically altering the combustor design or forfeiting its performance. Fuel is modulated in the frequency range of 0.6 to 5 Hz with various duty cycles [25–75%] using square wave. Fuel modulation is achieved by passing fuel through a direct current (DC) powered solenoid valve, which is being controlled using a custom-made circuit. The modulated fuel enters the combustor through an air-blast atomizer and is metered through a turbine flow meter. The main objective of this paper is to investigate the potential of active control to reduce combustion noise in laboratory scaled gas turbine combustor. Pressure transducer is used to capture the sound pressure level inside the combustor. A reduction in overall sound pressure level of 14dB is achieved by modulating fuel with 50% duty cycle at 1.5Hz.

4D Measurements and Analysis of Heat Release Rate in a Model Gas Turbine Combustor

2021 ◽  
Author(s):  
Rongxiao Dong ◽  
Qingchun Lei ◽  
Yeqing Chi ◽  
Qun Zhang ◽  
Wei Fan
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
Gas Turbine Combustor ◽  
Model Gas Turbine Combustor

Optical Measurement of Local and Global Transfer Functions for Equivalence Ratio Fluctuations in a Turbulent Swirl Flame

2013 ◽  
Author(s):  
Bernhard C. Bobusch ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Measurement ◽  
Low Frequencies ◽  
Fuel Flow ◽  
Calibration Measurement

Equivalence ratio fluctuations are known to be one of the key factors controlling thermoacoustic stability in lean premixed gas turbine combustors. The mixing and thus the spatio-temporal evolution of these perturbations in the combustor flow is, however, difficult to account for in present low-order modeling approaches. To investigate this mechanism, experiments in an atmospheric combustion test rig are conducted. To assess the importance of equivalence ratio fluctuations in the present case, flame transfer functions for different injection positions are measured. By adding known perturbations in the fuel flow using a solenoid valve, the influence of equivalence ratio oscillations on the heat release rate is investigated. The spatially and temporally resolved equivalence ratio fluctuations in the reaction zone are measured using two optical chemiluminescence signals, captured with an intensified camera. A steady calibration measurement allows for the quantitative assessment of the equivalence ratio fluctuations in the flame. This information is used to obtain a mixing transfer function, which relates fluctuations in the fuel flow to corresponding fluctuations in the equivalence ratio of the flame. The current study focuses on the measurement of the global, spatially integrated, transfer function for equivalence ratio fluctuations and the corresponding modeling. In addition, the spatially resolved mixing transfer function is shown and discussed. The global mixing transfer function reveals that despite the good spatial mixing quality of the investigated generic burner, the ability to damp temporal fluctuations at low frequencies is rather poor. It is shown that the equivalence ratio fluctuations are the governing heat release rate oscillation response mechanism for this burner in the low-frequency regime. The global transfer function for equivalence ratio fluctuations derived from the measurements is characterized by a pronounced low-pass characteristic, which is in good agreement with the presented convection–diffusion mixing model.

scholarly journals Combustion Instability of Swirl Premixed Flame with Dielectric Barrier Discharge Plasma

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1405
Author(s):  
Kai Deng ◽  
Shenglang Zhao ◽  
Chenyang Xue ◽  
Jinlin Hu ◽  
Yi Zhong ◽  
...  
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Instability ◽  
Premixed Flame ◽  
Oh Radicals ◽  
Acoustic Frequency ◽  
Planar Laser ◽  
Barrier Discharge Plasma

The effects of plasma on the combustion instability of a methane swirling premixed flame under acoustic excitation were investigated. The flame image of OH planar laser-induced fluorescence and the fluctuation of flame transfer function showed the mechanism of plasma in combustion instability. The results show that when the acoustic frequency is less than 100 Hz, the gain in flame transfer function gradually increases with the frequency; when the acoustic frequency is 100~220 Hz, the flame transfer function shows a trend of first decreasing and then increasing with acoustic frequency. When the acoustic frequency is greater than 220 Hz, the flame transfer function gradually decreases with acoustic frequency. When the voltage exceeds the critical discharge value of 5.3 kV, the premixed gas is ionized and the heat release rate increases significantly, thereby reducing the gain in flame transfer function and enhancing flame stability. Plasma causes changes in the internal recirculation zone, compression, and curling degree of the flame, and thereby accelerates the rate of chemical reaction and leads to an increase in flame heat release rate. Eventually, the concentration of OH radicals changes, and the heat release rate changes accordingly, which ultimately changes the combustion instability of the swirling flame.

DNS on Autoignition and Flame Propagation of Inhomogeneous Methane–Air Mixtures in a Closed Vessel

2011 ◽  
Author(s):  
Makito Katayama ◽  
Naoya Fukushima ◽  
Masayasu Shimura ◽  
Mamoru Tanahashi ◽  
Toshio Miyauchi
Keyword(s):  
Heat Release ◽  
Flame Propagation ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Kinetic Mechanism ◽  
Spatial Inhomogeneity ◽  
Closed Vessel ◽  
Isothermal Wall ◽  
Detailed Kinetic Mechanism

Direct numerical simulations (DNSs) on autoignition and flame propagation of inhomogeneous methane–air mixtures in a closed vessel are conducted with considering detailed kinetic mechanism and temperature dependence of transport and thermal properties. The mixtures with spatial inhomogeneity of temperature or equivalence ratio are investigated. Periodic condition for non-heatloss cases or isothermal wall condition for heatloss cases is imposed on the boundaries. From the DNS results without heatloss, effects of spatial inhomogeneity of temperature and equivalence ratio on mean heat release rate are clarified. Increase of spatial variations of temperature or equivalence ratio suppresses drastic rise of mean heat release rate and reduces its maximum value. Autoignition process is affected by temperature more strongly than equivalence ratio. In the cases with heatloss, ignition delay increases and the maximum mean heat release rate decreases. After autoignition process, propagating flame is formed along walls. Heat transfer characteristics in a closed vessel are also discussed with combustion mechanisms.

Synchronization During Multi-Mode Thermoacoustic Oscillations in a Liquid-Fueled Gas Turbine Combustor at Elevated Pressure

2019 ◽  
Author(s):  
Mitchell L. Passarelli ◽  
J. D. Maxim Cirtwill ◽  
Timothy Wabel ◽  
Adam M. Steinberg ◽  
A. J. Wickersham
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
High Speed ◽  
Elevated Pressure ◽  
Fuel Injector ◽  
Frequency Pulling ◽  
Industrial Gas Turbine ◽  
Thermoacoustic Oscillations

Abstract This paper analyzes intermittent self-excited thermoacoustic oscillations in which the pressure (P′) and heat release rate (q̇′) fluctuations are harmonically coupled. That is to say, P′ and q̇′ do not oscillate at the same frequencies, but rather at frequencies in integer ratios. Thus, this system represents a case dominated by nonlinear cross-mode coupling. The measurements were obtained in an optically-accessible combustor equipped with an industrial gas turbine fuel injector operating with liquid fuel under partially-premixed conditions at elevated pressure. High-speed chemiluminescence (CL) imaging of OH* was used as an indicator of the heat release rate. The data was processed using spectral proper orthogonal decomposition (SPOD) to isolate the dominant heat release and pressure modes. Synchronization theory was used to determine when the modes are coupled and how their interaction manifests in the measurements, particularly how it relates to the observed intermittency. The results show three distinct intervals of synchronized oscillation shared by all the mode pairs analyzed. The first interval exhibits the same characteristics as a pair of noisy, phase-locked self-oscillators, with phase-slipping and frequency-pulling. While the behaviour of the second interval differs among mode pairs, strong frequency-pulling is observed during the third interval for all pairs.

scholarly journals On the Local Heat Release Rate in a Combustion Chamber of Gas Turbine

1962 ◽  
Vol 5 (19) ◽  
pp. 505-510
Author(s):  
Takashi SATO ◽  
Itaru MICHIYOSHI ◽  
Ryuichi MATSUMOTO
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
Local Heat
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