Effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustor

2020 ◽  
Vol 32 (4) ◽  
pp. 047101
Author(s):  
Mohammad Shahsavari
Keyword(s):  
Thermoacoustic Instabilities ◽  
Fresh Mixture ◽  
Lean Premixed

Effects of Intrinsic Flame Instabilities On Thermoacoustic Oscillations in Lean Premixed Gas Turbines

2022 ◽  
Author(s):  
Fangyan Li ◽  
Xiaotao Tian ◽  
Ming-long Du ◽  
Lei Shi ◽  
Jiashan Cui
Keyword(s):  
Heat Release ◽  
Gas Turbines ◽  
Lewis Number ◽  
Acoustic Mode ◽  
Longitudinal Distribution ◽  
Unstable State ◽  
Rocket Motors ◽  
Thermoacoustic Instability ◽  
Thermoacoustic Instabilities ◽  
Lean Premixed

Abstract Thermoacoustic instabilities are commonly encountered in the development of aeroengines and rocket motors. Research on the fundamental mechanism of thermoacoustic instabilities is beneficial for the optimal design of these engine systems. In the present study, a thermoacoustic instability model based on the lean premixed gas turbines (LPGT) combustion system was established. The longitudinal distribution of heat release caused by the intrinsic instability of flame front is considered in this model. Effects of different heat release distributions and characteristics parameters of the premixed gas (Lewis number Le, Zeldovich Number and Prandtl number Pr) on thermoacoustic instability behaviors of the LPGT system are investigated based on this model. Results show that the LPGT system features with two kinds of unstable thermoacoustic modes. The first one corresponds to the natural acoustic mode of the plenum and the second one corresponds to that of the combustion chamber. The characteristic parameters of premixed gases have a large impact on the stability of the system and even can change the system from stable to unstable state.

Model Based Active Combustion Control Concept for Reduction of Pulsations and NOx Emissions in Lean Premixed Gas Turbine Combustors

2008 ◽  
Author(s):  
Ernst Schneider ◽  
Stephan Staudacher ◽  
Bruno Schuermans ◽  
Haiwen Ye
Keyword(s):  
Gas Turbine ◽  
Gaussian Processes ◽  
Nox Emissions ◽  
Combustion Control ◽  
Model Based Control ◽  
Thermoacoustic Instabilities ◽  
Gas Turbine Combustors ◽  
Model Based ◽  
Lean Premixed ◽  
Control Concept

Strict environmental regulations demand gas turbine operation at very low equivalence ratios. Premixed gas turbine combustors, operated at very lean conditions, are prone to thermoacoustic instabilities. Thermoacoustic instabilities cause significant performance and reliability problems in gas turbine combustors, so their prevention is a general task. Splitting the fuel mass flow between different burner groups, i.e. using a burner group fuel staging technique, is a possibility to control the thermoacoustic instabilities. The resulting combustion perturbations have also effects on the gas turbine NOx emissions making it necessary to find an optimum balance between pulsations and emissions. This paper presents a model based active combustion control concept for the reduction of pulsations and emissions in lean premixed gas turbine combustors. The model is integrated in an observer structure derived from a Luenberger observer. The control logic is based on a PID algorithm allowing either the direct command of the pulsation level with a continuous monitoring and a potential limit setting of the NOx emission level or vice versa. The gas turbine pulsations and emissions are modelled using Gaussian Processes. - Gaussian Processes are stochastic processes related to Neural Networks that can approximate arbitrary functions. Based on measured gas turbine data they can be implemented in an easy and straightforward manner. The model provides the control system with real time data of the outputs resulting from settings of the staging ratio that is the actuating variable of the system. A model based control concept can significantly alleviate the effects of time delays in the system. The model based control concept allows for fast adaptation of the burner group staging ratio during static and transient operations to achieve an optimum of the pulsation and emission levels. During tests the model based control concept gave good results and proved to be robust even at high disturbance levels.

Thermo-Acoustic Interactions in a Premixed Dump Combuster

2002 ◽  
Author(s):  
S. Galvin ◽  
J. A. Fitzpatrick
Keyword(s):  
Heat Release ◽  
Research Effort ◽  
Lean Premixed Combustion ◽  
Thermoacoustic Instabilities ◽  
The Past ◽  
Lean Premixed ◽  
Prediction And Control ◽  
Modelling Techniques ◽  
And Control ◽  
Phase Relationships

There is significant interest in the interaction of parameters associated with lean premixed combustion because the demand for reduced emissions has led to an increased usage of this type of system. Thermoacoustic instabilities, which arise as a consequence of unsteady pressure and heat release interactions, are known to occur frequently for these lean premixed configurations. There has been a substantial research effort in the past decade directed at the development of modelling techniques for the prediction and control of these instabilities. Tests have been performed in an optically accessible dump combustor for a range of equivalence ratio with two different dump or expansion ratios and a number of flow rates. Both thermoacoustic and flow/acoustic interactions are observed over a large operating range. The pressure and heat release autospectra and cross-spectra were calculated and their coherence and phase relationships are examined to determine their interaction including the applicability of the Rayleigh criterion.

Low-Order Modelling of the Response of Ducted Flames in Annular Geometries

2012 ◽  
Author(s):  
Owen S. Graham ◽  
Ann P. Dowling
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Network Model ◽  
Time Domain ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Fuel Injectors ◽  
Thermoacoustic Instabilities ◽  
Lean Premixed

The adoption of lean premixed prevaporised combustion systems can reduce NOx emissions from gas turbines, but unfortunately also increases their susceptibility to thermoacoustic instabilities. Initially, acoustic waves can produce heat release fluctuations by a variety of mechanisms, often by perturbing the equivalence ratio. If correctly phased, heat release fluctuations can subsequently generate more acoustic waves, which at high amplitude can result in significant structural damage to the combustor. The prediction of this phenomenon is of great industrial interest. In previous work, we have coupled a physics based, kinematic model of the flame with a network model to provide the planar acoustic response necessary to close the feedback loop and predict the onset and amplitude of thermoacoustic instabilities in a lab-scale, axisymmetric single burner combustor. The advantage of a time domain approach is that the modal interaction, the influence of harmonics, and flame saturation can be investigated. This paper extends this approach to more realistic, annular geometries, where both planar and circumferential modes must be considered. In lean premixed prevaporised combustors, fluctuations in equivalence ratio have been shown to be a dominant cause of unsteady combustion. These can occur, for example, due to velocity perturbations in the premix ducts, which can lead to equivalence ratio fluctuations at the fuel injectors, which are subsequently convected downstream to the flame surfaces. Here, they can perturb the heat release by locally altering the flame speed, enthalpy of combustion, and, indirectly, the flame surface area. In many gas turbine designs, particularly aeroengines, the geometries are composed of a ring of premix ducts linking a plenum and an annular combustor. The most unstable modes are often circumferential modes. The network model is used to characterise the flow response of the geometry to heat fluctuations at an appropriate location, such as the fuel injectors. The heat release at each flame holder is determined in the time domain using the kinematic flame model derived, as a function of the flow perturbations in the premix duct. This approach is demonstrated for an annular ring of burners on a in a simple geometry. The approach is then extended to an industrial type gas turbine combustor, and used to predict the limit cycle amplitudes.

scholarly journals Experimental investigation of equivalence ratio fluctuations in a lean premixed kerosene combustor

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
Manuel Vogel ◽  
Michael Bachfischer ◽  
Jan Kaufmann ◽  
Thomas Sattelmayer
Keyword(s):  
Equivalence Ratio ◽  
Background Radiation ◽  
Optical Measurement ◽  
Distortion Correction ◽  
Atmospheric Conditions ◽  
Imaging Spectrometer ◽  
Thermoacoustic Instabilities ◽  
Steady State Operation ◽  
Wide Range ◽  
Lean Premixed

Abstract In this study a measurement technique for determination of equivalence ratio fluctuations from flame chemiluminescence in a kerosene-fuelled lean premixed combustor under atmospheric conditions is presented. Firstly, fundamental investigations into the relationship between the ratio of different chemiluminescence signals and the equivalence ratio are carried out using an imaging spectrometer. The chemiluminescence intensity is recorded for a wide range of equivalence ratios and fuel mass flows during steady state operation. The spectra show that the CH*/OH* ratio depends linearly on the equivalence ratio and is independent of the mass flow in the investigated range. Moreover, the background radiation has no influence on the monotonous trend of the CH*/OH* ratio for kerosene combustion. This interesting finding opens up new possibilities for passive optical measurement of the equivalence ratio in kerosene flames. Bandpass-filtered phase-correlated images of OH* and CH* chemiluminescence of an acoustically excited flame are taken simultaneously on one camera chip using an image doubler. After distortion correction, the image pair is used to calculate the global equivalence ratio from the CH*/OH* ratio. Based on the calibration chart derived in stationary operation, phase-resolved equivalence ratio perturbations are determined during acoustic excitation. The presented technique allows a quantitative measurement of equivalence ratio fluctuations in spray combustion and can therefore provide a better understanding of the fundamental mechanisms of thermoacoustic instabilities triggered by equivalence ratio fluctuations. Graphic abstract

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.

Development and Validation of a 1-D Tool for Thermoacoustic Instabilities Analysis in Gas Turbine Combustors

2008 ◽  
Author(s):  
A. Andreini ◽  
B. Facchini ◽  
L. Mangani ◽  
F. Simonetti
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Nodal Point ◽  
Mean Flow ◽  
Combustion Heat ◽  
Thermoacoustic Instabilities ◽  
Lumped Parameter ◽  
Resonance Frequencies ◽  
Lean Premixed ◽  
Energy Equations

In the last years, the more restrictive environmental legislations have constrained gas turbine manufacturers to the development of new low-emission combustors. Lean Premixed technology has become a necessary standard to meet emissions requirements and allowing an heavy reduction of nitrogen oxides emission. This kind of technology, due to the use of lean premixed mixtures, is severely affected by thermoacoustic phenomena which cause damages to combustor components and consequently reduce the overall gas turbine life of a factor of two or more. Specifically, premixed flames pose the threat of pressure oscillations. This phenomenon is the effect of the strong interaction between combustion heat-release and fluid dynamics aspects. In order to investigate thermoacoustic instabilities, a mono-dimensional code was developed and validated. It takes into account only longitudinal frequencies and it is thought to be highly modular to modify or add blocks, corresponding to different thermoacoustic models. The tool is based on a lumped-parameter approach, which consists in considering constant mean flow quantities over each fundamental straight duct element and a nodal point at each duct interface. For each interface, where an acoustic impedance could be present, the linearized fluctuating mass, momentum and energy equations are solved including entropic waves. To validate such tool, several tests, referring to actual test rigs and experimental gas turbine combustor geometries, were performed. The results show a general agreement with empirical data and other numerical results reported in literature in terms of resonance frequencies, stability and modal shapes, both for no flame and fluctuating heat release cases.

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