Acoustic Control of Thermoacoustic Instabilities Using Experimental Model-Based Controllers (original) (raw)

Active control of combustion instabilities using model-based controllers

Combustion Science and Technology, 2003

This paper presents an implementation of active control of thermoacoustic instabilities on a swirl-stabilized spray combustor. Loudspeakers were used as control actuators in the closedloop control scheme. Pressure transducers located in the combustion chamber produced the feedback signal in the control study. Experimental models of the combustor dynamics were developed using a non-parametric identification method. LQG, LQG/LTR and H ∞ loop-shaping controllers were derived and tested in simulation as well as experimentally. Phase-delay control was used as a baseline method to compare the performance of these different controllers. The advantages of the model-based controllers over the baseline strategy are clearly presented.

Thermoacoustic Instabilities: Modeling and Control

… on Control Systems …, 2003

The goal of this study was twofold. First, modelling strategies were proposed to characterize the dynamics driving the thermoacoustic instabilities in a swirl-stabilized premixed burner. Secondly, this model was used to synthesize controllers in order to apply active control strategies to suppress this phenomenon. An experimental combustor model based on acoustic properties of the combustion chamber was derived. This model separates the combustor into a 4-block linear system. Acoustic and fuel modulations were used to obtain the frequency response of each block representing a part of the combustor test-rig. Using this linear representation H∞ Disturbance Rejection and H∞ Loop-Shaping controllers were computed and tested for a set of different working conditions of the chamber for the robustness of the resulting controllers. Standard phase-delay control was used as baseline control strategy to judge the performance of the proposed controllers. Experimental results show the advantages of these model-based control strategies to suppress thermoacoustic instabilities in the test-rig.

Thermoacoustic instability: model-based optimal control designs and experimental validation

IEEE Transactions on Control Systems Technology, 2000

Active control of thermoacoustic instability has been increasingly sought after in the past two decades to suppress pressure oscillations while maintaining other performance objectives such as low NO x emission, high efficiency and power density. Recently, we have developed a feedback model of a premixed laminar combustor which captures several dominant features in the combustion process such as heat release dynamics, multiple acoustic modes, and actuator effects [1]. In this paper, we study the performance of optimal control designs using the model in [1] with additional effects of mean heat and mean flow, actuator dynamics, and input saturation. These designs are verified experimentally using a 1kW bench-top combustor rig and a 0.2W loudspeaker over a range of flow rates and equivalence ratios. Our results show that the proposed controllers, which are designed using a two-mode finite dimensional model, suppress the thermoacoustic instability significantly faster than those obtained using empirical approaches in similar experimental setups without creating secondary resonances, and guarantee stability robustness.

A linear model for control of thermoacoustic instabilities on annular domain

2003

We present a distributed linear model of thermoacoustic instability in form of a set of coupled PDEs including an acoustic model based on Potential Euler formulation, a fully distributed fuel transport model based on advection equation, and a fuel-sensitive heat release model based on assumption of fixed flame location. The damping in the distributed model is provided on the acoustic boundaries using local acoustic impedance models. The model is suitable for analysis and control of multiple acoustic modes in annular combustors with bluff body stabilized flames and for optimization of fuel control architecture. We also derive a low order model for control using Galerkin projection of the Potential Euler equations on finite number of acoustic basis functions and analytically solving the linearized fuel advection equation. The resulting frequency domain model has a form of coupled system involving undamped oscillators representing acoustic modes, distributed delays representing effect of acoustic perturbation on the fuel transport and combustion, and positive real transfer functions representing acoustic impedances of the boundaries. A simple control algorithm to suppress pressure oscillations is derived using the reduced order model.

Linear control strategies for the suppression of flame instabilities

2005

The use of low NO x premixed burners with a large modulation range in modern central heating systems often leads to noise problems. These problems are often solved by passive techniques. In this study, the use of active model-based control strategies to interrupt the interaction between acoustic waves and unsteady heat-release is investigated in simulations and experiments. It is found that, though based on a linearized model, the LQG/LTR control and H ∞ control are effective.

Passive control of thermoacoustic instabilities in swirl-stabilized combustion at elevated pressures

International Journal of Spray and Combustion Dynamics

In this study, a porous insert is placed at the dump plane of a swirl-stabilized lean premixed combustor to passively suppress thermoacoustic instabilities. The diffuser-shaped annular ring of porous inert material influences the turbulent flow field directly, including recirculation zones and vortical and/or shear layer structures to passively control the acoustic performance of the combustor. The porous inert material is made of silicon carbide-hafnium carbide coated, high-strength, high-temperature-resistant open-cell foam materials. In this study, the porous insert concept is investigated at above-ambient operating pressures to demonstrate its suitability for practical combustion applications. Experiments are conducted in quartz and metal combustors, without and with the porous insert while varying operating pressure, equivalence ratio, and reactant flow rate. Measurements show that the porous insert, and consequent changes in the combustor flow field, decrease the sound pressure levels at the frequency of combustion instability at all operating conditions investigated in this study. The porous insert also decreases the broadband combustion noise, i.e. the measured sound pressure levels over a wide frequency range.

Effects of liquid fuel/wall interaction on thermoacoustic instabilities in swirling spray flames

Combustion and Flame, 2020

Computational prediction of thermoacoustic instabilities arising in gas turbine and aero-engine combustors still remains a challenge especially if fuel is injected in a liquid spray form. This study shows that, in LES of such a combustor, the treatment of the liquid fuel film created on the walls of the injection system affects the mean flame weakly, but modifies the flame dynamics strongly. The configuration used for this work is the experimental setup SICCA-spray available at EM2C laboratory in Paris. First steady spray flame measurements are used to validate the LES Euler-Lagrange approach. Two modelling strategies for the interaction between the liquid fuel and the injector walls are tested with a negligible impact on the flame shape and structure. In the second part the same comparison is applied to another operating condition where a self-sustained thermo-acoustic limit-cycle is experimentally observed. In that case resonant coupling is achieved with LES, confirming the adequacy of the approach but only when the film layer is taken into account. Indeed, contrarily to the stable configuration, the difference between the two Lagrangian boundary conditions is shown to have a major impact on the feedback mechanism leading to the thermoacoustic oscillation.

Uncertainty Quantification of Thermoacoustic Instabilities in a Swirled Stabilized Combustor

2015

Combustion instabilities can develop in modern gas-turbines as large amplitude pressure oscillations coupled with heat release fluctuations. In extreme cases, they lead to irreversible damage which can destroy the combustor. Prediction and control of all acoustic modes of the configuration at the design stage are therefore required to avoid these instabilities. This is a challenging task because of the large number of parameters involved. This situation becomes even more complex when considering uncertainties of the underlying models and input parameters. The forward uncertainty quantification problem is addressed in the case of a single swirled burner combustor. First, a Helmholtz solver is used to analyze the thermoacoustic modes of the combustion chamber. The Flame Transfer Function measured experimentally is used as a flame model for the Helmholtz solver. Then, the frequency of oscillation and the growth rate of the first thermoacoustic mode are computed in 24 different operatin...