The main goal of this work was to develop adaptive filter algorithms and test their performance in active combustion control. Several algorithms were incorporated, which are divided into gradient descent algorithms and pattern searches. The algorithms were tested on three separate platforms. The first was an analog electronic simulator, which uses a second order acoustics model and a first order low pass filter to simulate the flame dynamics of an unstable tube combustor. The second was a flat flame, methane-air Rijke tube. The third can be considered a quasi-LDI liquid fuel combustor with a thermal output of approximately 30 kW. Actuation included the use of an acoustic actuator for the Rijke tube and a proportional throttling valve for the liquid fuel rig. Proportional actuation, pulsed actuation, and subharmonic control were all investigated throughout this work. The proportional actuation tests on the Rijke tube combustor have shown that, in general, the gradient descent algorithms outperformed the pattern search algorithms. Although, the pattern search algorithms were able to suppress the pressure signal to levels comparable to the gradient descent algorithms, the convergence time was lower for the gradient descent algorithms. The gradient algorithms were also superior in the presence of actuator authority limitations. The pulsed actuation on the Rijke tube showed that the convergence time is decreased for this type of actuation. This is due to the fact that there is a fixed amplitude control signal and algorithms did not have to search for sufficient magnitude. It was shown that subharmonic control could be used in conjunction with the algorithms. Control was achieved at the second and third subharmonic, and control was maintained for much higher subharmonics. The cost surface of the liquid fuel rig was obtained as the mean squared error of the combustor pressure as a function of the magnitude and phase of the controller. The adaptive algorithms were able to achieve some suppression of the pressure oscillations but did not converge to the optimal phase as shown in the cost surface. Simulations using the data from this cost surface were also performed. With the addition of a probing function, the algorithms were able to converge to a near-optimal condition. / Master of Science

Active control of combustion instabilities through secondary fuel injection is a control method that has gained a lot of attention in the past decade. Previous control schemes with acoustic loudspeakers are not practical in full-scale gas turbines due to the extreme temperatures and acoustic power requirements. Much work has gone into controlling these thermoacoustic instabilities with secondary fuel control. Control of a laminar premixed tube combustor through secondary fuel actuation is the concentration of this work. It is the first known published attempt to control a laminar premixed tube combustor through secondary fuel actuation. Due to the low flow rates within the tube combustor an innovative injection technique had to be constructed to perform the secondary fuel actuation. The gaseous fuel is injected only one millimeter above the location of the flame through one, two, or four injectors. These injectors were designed to overcome the serious problem of pulse diffusion. This technique enabled the tube combustor to be controlled through secondary fuel injection. Accompanying the innovative fuel injection technique is a duty cycle modulation technique that was a prime contributor to the success of the control system. This method enabled the system to be controlled at conditions that were uncontrollable with a fixed duty cycle. The overall result was a 35 dB suppression of the limit cycle amplitude with 20% secondary fuel injection. / Master of Science

No description available.

No description available.

This last decade experienced a sudden increase of interest in the control of thermo-acoustic instabilities, in particular through the use of fuel modulation techniques. The primary goal of this research was to design, construct and characterize a high bandwidth proportional fuel injection system, which could be used to study the effect of specific levels of fuel modulation on the combustion process and the reduction of thermo-acoustic instabilities. A fuel injection system, incorporating the use of a closed loop piston and check valve, was designed to modulate the primary fuel supply of an atmospheric liquid-fueled swirl stabilized combustor operating at a mean volumetric fuel flow rate of 0.4 GPH. The ability of the fuel injection system to modulate the fuel was examined by measuring the fuel line pressure and the flow rate produced during operation. The authority of this modulation over the combustion process was investigated by examining the effect of fuel modulation on the combustor pressure and the heat release of the flame. Sinusoidal operation of the fuel injection system demonstrated: a bandwidth greater that 800 Hz, significant open loop authority (averaging 12 dB) with regards to the combustor pressure, significant open loop authority (averaging 33 dB) with regards to the unsteady heat release rate and an approximate 8 dB reduction of the combustor pressure oscillation present at 100 Hz, using a phase shift controller. It is possible to scale the closed loop piston and check valve configuration used to create the fuel injection system discussed in this work to realistic combustor operating conditions for further active combustion control studies. / Master of Science

The first part of this work focuses on control experiments performed on an unstable kerosene-fueled turbulent combustor. Using a phase shift controller and primary fuel modulation stability is successfully gained for a wide band of global equivalence ratios allowing the limitations of the control scheme to be characterized. It is shown that control signal saturation can significantly impact the ability of the control scheme to stabilize the system. Three different regions of controllability are defined based on the degree of saturation. A hysteresis behavior is also found to exist for the controller settings depending on whether stability is being maintained or realized for an unstable system. The second part of this work focuses on the impact that primary fuel modulation has on the fuel spray. Measurements for a simplex nozzle and an air-assist nozzle are taken under both static and dynamic operating conditions with a Phase Doppler Anemometry system. The dynamic modulation is found to significantly impact the spray properties of both nozzles. / Master of Science

Thermoacoustic instabilities are a problem in modern pre-mixed combustors causing reduced performance and leading in the extreme to combustor failure from excessive pressure cycles. Much work has been done using linear controllers to eliminate these instabilities. Many experimenters in the field have used pulsed and subharmonic fuel controllers to eliminate these instabilities, but very little investigative work has been done on these controllers. The goal of this work is to explain the mechanism of control behind pulsed controllers. It is shown that the combustion system can be treated as a linear system, thus meaning that frequency components of the control signal at the desired instability frequency are the dominant means of control, with nonlinear effects only serving to slightly reduce the gain necessary for control. Fourier analysis is thus performed on pulsed signals and the components analyzed, showing that there will indeed be a component of a pulsed signal at the frequency of the instability, aside from a few select cases. It is then proven that this frequency component is largely responsible for control of the thermoacoustic system using proportional height pulse train signals, which will change pulse height based on the amplitude of the instability. This analysis is then used to predict the height of instabilities resulting from the use of fixed height pulse control signals. Finally, numerical simulations and experimental observations support the analytical constructs. Acoustic control is mainly used for these experiments, although some preliminary work with liquid fuel controllers is also presented. / Master of Science

High-bandwidth fuel modulation is currently one of the most promising methods for active combustion control. To attenuate the large pressure oscillations in the combustion chamber, the fuel is pulsed so that the heat release rate fluctuations damp the pressure oscillations in the combustor. This thesis focuses on the development and implementation of a high-bandwidth, proportional modulation system for liquid-fuel active combustion control. The throttle valve modulation system, discussed in this thesis, uses a 500-um piezoelectric stack coupled with an off-the-shelf valve. After comparing three other types of actuators, the piezoelectric stack was selected because of its compact size, bandwidth capabilities, and relatively low cost. Using the acoustic resonance of the fuel line, the system is able to achieve 128% pressure modulation, relative to the mean pressure, and is capable of producing more than 75% flow modulation at 115 Hz. Additionally, at 760 Hz the system produces 40% pressure modulation and 21% flow modulation with flow rates between 0.4 and 10 gph. Control authority was demonstrated on a single-nozzle kerosene combustor which exhibits a well-pronounced instability at ~115 Hz. Using the modulation system, the fundamental peak of the combustion instability was reduced by 30 dB, and the broadband sound pressure levels inside the combustor were reduced by 12 dB. However, the most important conclusion from the combustion control experiments was not the system?s accomplishments, but rather its inability to control the combustor at high global equivalence ratios. Our work indicates that having the ability to modulate a large percentage of the primary fuel is not always sufficient for active combustion control. / Master of Science

Η παρούσα διατριβή μελετά τις δυνατότητες υπολογισμού του πεδίου ροής δύο λειτουργικών παραμέτρων συμπεριλαμβανομένων του εκπεμπόμενου θορύβου και των εκπεμπόμενων ρύπων. Εξετάζεται η αλληλεπίδραση της καύσης με το ρευστο-θερμοδυναμικό πεδίο και τις χημικές αντιδράσεις. Περιγράφονται συνοπτικά οι διέπουσες εξισώσεις, οι μέθοδοι και τα μοντέλα της τυρβώδους καύσης και επισημαίνονται τα πλεονεκτήματα του μοντέλου των μεγάλων δινών (LES) το οποίο επιλέχθηκε εδώ. Αναπτύσσεται ένας εύχρηστος, από την ρευστοδυναμική υπολογιστική μεθοδολογία, πολυβηματικός μηχανισμός για δύο καύσιμα άμεσου ενδιαφέροντος το μεθάνιο και το προπάνιο. Προτείνεται, δηλαδή, ένα απλοποιημένο χημικό σχήμα για την οξείδωση των βασικών καυσίμων το οποίο περιέχει τον σχηματισμό του NΟx και της παραγωγής καπναιθάλης. Μετά από ανάλυση του ρόλου της καύσης στην ακουστική διακρίνονται οι δύο χαρακτηριστικοί τύποι: του θορύβου τυρβώδους καύσης (βόμβος – roar) και του θορύβου από τις ταλαντώσεις της καύσης (combustion oscillation). Παρουσιάζεται η κυματική εξίσωση και εισάγεται η έννοια του θερμο-ακουστικού όρου ο οποίος είναι συνάρτηση της απελευθερωμένης θερμότητας (q) στην φλόγα και εμφανίζεται ως όρος πηγής στην βασική εξίσωση. Στη συνέχεια η φλόγα εξετάζεται ως αυτόνομος πηγή αλλά και ως ενισχυτής θορύβου. Με την προσέγγιση της Προσομοίωσης των Μεγάλων Δινών (Large Eddy Simulation, LES) αναπτύχθηκε μια μεθοδολογία υπολογισμού του θορύβου που εκπέμπεται από το μέτωπο τυρβωδών φλογών διάχυσης. Στο πλαίσιο της προτεινομένης μεθοδολογίας το αποτέλεσμα ήταν η ανάπτυξη ενός τρισδιάστατου προγνωστικού υπολογιστικού κώδικα. Στην συνέχεια υπολογίζεται το αεροθερμοδυναμικό τυρβώδες πεδίο ροής μέσω τελειοποίησης κωδίκων του Εργαστηρίου Τεχνικής Θερμοδυναμικής, των κωδίκων που αναπτύχθηκαν στο πλαίσιο της παρούσης εργασίας αλλά και του εμπορικού κώδικα Fluent. Η μεθοδολογία, που αναπτύχθηκε με την παρούσα ερευνητική εργασία, πιστοποιήθηκε μέσω μιας σειράς πρωτότυπων μετρήσεων, του εκπεμπόμενου θορύβου στις συρρέουσες, εφαπτόμενες και ανυψωμένες και ανακυκλοφορούσες (χαμηλού και υψηλού λόγου καυσίμου/αέρα) φλόγες, σε πρωτότυπες πειραματικές διατάξεις του Εργαστηρίου. Συγκεκριμένα διαμορφώθηκε ένας καινοτόμος αεροδυναμικός φλογοσυγκρατητής πολλαπλών εγχύσεων που διατηρεί μια πλούσια γκάμα φλογών με ιδιαίτερα χαμηλό λόγο καυσίμου/αέρα. Επιτεύχθηκαν πειραματικές μετρήσεις, του ορμικού και θερμοκρασιακού πεδίου διαφόρων μορφών τυρβωδών φλογών, συντάχθηκαν σχετικά διαγράμματα και υπολογίσθηκαν οι αρχικές και οριακές συνθήκες των πειραμάτων. / In the present work the calculation of two parameters, the radiated noise and pollutants are studied. The interaction between combustion, the aerothermodynamical field and the chemical reactions is studied. The equations, the methods and the models of turbulent combustion are described here and the advantages of the large eddy simulation model (LES) which has been chosen for this case, are marked. A multi-step chemistry mechanism is developed for two fuels of great interest: methane and propane. A simple chemical scheme for the oxidation of basic fuels which includes the formation of NOx and soot is suggested in the present work. After analyzing the role of combustion in the acoustics two types of noise are distinguished the turbulent combustion noise and the noise from combustion oscillation. The wave equation is presented and the definition of thermo acoustic term which is a function of the heat release q in flame and it appears as a source term in the basic equation. The flame is examined as an autonomous source as well as a noise amplifier. With the approach of large eddy simulation (LES) a methodology for the noise calculation is developed which noise is from the turbulent diffusion flame front. In the place of the suggested methodology the result was the development of a 3-D computational code. The turbulent aerothermodynamical flow field is computed by codes has been developed in the laboratory of technical thermodynamic and by the commercial code (fluent). The methodology, which has been developed in the present work, has been certificated through a series of original measurements of the emitted noise in coaxial, tangential and lifted flames in original experimentallayouts.