Please use this identifier to cite or link to this item: http://dx.doi.org/10.14279/depositonce-2964
Main Title: Interactions of Flow Field and Combustion Characteristics in a Swirl Stabilized Burner
Translated Title: Interaktionen von Strömungsfeld und Verbrennungscharakteristiken in einem drallstabilisierten Brenner
Author(s): Emara, Ahmed Abdelrazek
Advisor(s): Paschereit, Christian Oliver
Granting Institution: Technische Universität Berlin, Fakultät V - Verkehrs- und Maschinensysteme
Type: Doctoral Thesis
Language: English
Language Code: en
Abstract: Die vorliegende Arbeit beschäftigt sich mit Verbrennungscharakteristiken, Strömungsfelduntersuchungen sowie Wechselwirkungen des Strömungsfeldes in einem drallstabilisierten Brenner. Das Hauptziel ist es, eine stabile Verbrennung bei geringen Emissionen zu gewährleisten. Um das zu erreichen, werden drei Ideen untersucht. Die erste Idee ist die Verwendung eines neuen Modells eines in den Brenner integrierten rückgekoppelten fluidischen Oszillators. Die zweite ist die Modulation einer in denselben Brenner eingelassenen Piloteinspritzdüse, die mit mehreren Löchern versehen ist. Die letzte Idee umfasst eine Änderung des Brennerauslasses und der akustischen Randbedingung. Der fluidische Oszillator hat keine beweglichen Teile oder Ventilregelungen, nur die Fluidbewegung selbst ist verantwortlich für die Erzeugung einer pulsienden Strömung. Die Schwingung erfolgt selbsterregt. Untersucht werden das Strömungsverhalten im inneren und äußeren Bereich des fluidischen Oszillators sowie dessen Verhalten in aktiven Kontrollregelungen. Die optimale Oszillatorkonstruktion überwindet dabei Größeneinschränkungen sowie Hochfrequenzstörungen bedingt durch Hochdruckschwingungen und wird im Brenner unter reagierenden und nichtreagierenden Bedingungen getestet. Das kohärente Strömungsfeld und die Wechselwirkung zwischen Eindüsung und Brennerströmungsfeld werden an drei koaxialen Positionen im Brenner nachgewiesen. Die Frequenzanalyse der Signale bei verschiedenen Massenströmen zeigt einen linearen Zusammenhang für das gewählte Schwingungsmodell auf. Die Druckschwankungen liegen in sicherer Distanz zu den erwarteten Verbrennungsinstabilitäten. Die Strouhalzahl ist nahezu linear im untersuchten Bereich. Der zweite Teil hat die Zielsetzung, die Wirkung unterschiedlicher Piloteindüsungen auf die Stabilität, die Emissionen und das Strömungsfeld in einem industrienahen, drallstabilisierten Brenner bei verschiedenen akustischen Randbedingungen (kurzer und langer Brennkammerraum) zu erklären. Die Art der Eindüsung (Brennstoff mit/ohne Luft, nur Luft) sowie Form und Position (im Brenner unten, mittig, oben) der Düse werden bei konstantem globalen Äquivalenzverhältnis überprüft. Die Eindüsung von über das Hauptrohr transferierter Luft durch die Pilotlanze und einer im Brenner unten liegenden Piloteinspritzdüse zeigen die besten Resultate. Die Unterdrückung von Instabilitäten wird bei magerer Verbrennung erreicht. Der letzte Teil dieser Arbeit beschäftigt sich mit Änderungen des Dralls in der Strömung, welcher stark durch die Auslassbedingungen der Brennkammer beeinflusst wird. Untersucht wird dies mittels eines industrienahen, drallstabilisierten Brenners unter nichtreagierenden Strömungsbedingungen. Die Brennkammerlänge und das Auslasskontraktionsverhältnis werden variiert und ergeben die größte Änderung im Strömungsfeld bei einer kurzen Brennkammer und dem kleinsten Kontraktionsverhältnis. Die verwendeten Messtechniken sind Mikro- und Hydrofone, PIV, LIF, Hitzdrahtanemometrie, Thermoelemente, Gasanalysatoren und OH* Chemilumineszenz-Photomultiplier mit Kamera.
This work deals with combustion characteristics, flow field investigations, and flow field interaction in a swirl-stabilized burner. The main goal is to provide stable combustion at low emissions. To achieve this in the combustor, three concepts are inspected. The first one is applied by using a new model of feedback fluidic oscillator (designed, modulated, and manufactured at TU Berlin) integrated with the burner. The second concept is modulating a new multi-hole pilot injector inserted into the same swirl-stabilized burner. The last concept is by changing of the combustor outlets and acoustic boundary conditions. The fluidic oscillator has no moving parts or valve arrangements but the fluid movement itself is responsible of generating a pulsed flow. The oscillation comes without any external excitation and is described as self-exciting. The behavior of the fluid flow inside and outside the fluidic oscillator is studied as well as the oscillator performance in active control schemes which include high-frequency flow modulation. The optimum oscillator design overcomes size restrictions and higher frequency penalties reproduced from higher pressure oscillations and it is tested inside the swirl stabilized burner at non-reacting and reacting conditions. Phase averages reconstructed on proper orthogonal decomposition (POD) as well as acoustic measurements was used to characterize the coherent structures shed from the oscillator and the burner. The coherent flow field and the interaction between injector and burner flow field are demonstrated at three proposed coaxial mounting positions inside the burner. The frequency contents of the signals at different mass flows show a linear representation for the proposed oscillator model. The pressure oscillations also lie in a safe range far from expected combustion instabilities. The Strouhal number is almost linear at a specified range which contains the combustion investigations. Influence of this oscillator on stability and combustion control is demonstrated by implementing some transfer of the main fuel, air or both inside the fluidic oscillator, in an attempt to enhance the combustion performance at a constant overall equivalence ratio. The air transfer inside the oscillator (2.73%) is the best way to reduce the emissions at the whole coaxial mounting positions while the combustion is free of instabilities. Some small amounts of fuel transfer plus air inside the fluidics may be also useful in reduction of nitrogen oxides at low values of carbon monoxide and at stable conditions. It was determined that the optimum mounting position of the fluidics was at the underside the burner. So, the fluidics may have an advantage to work better with some new or other burner configurations and different positions inside the burner to reduce emissions and instabilities which, in turn, enhances the combustion and complies with global environmental laws at the whole world. The second part aims to explain the effect of different pilot injections of the new pilot injector on stability, emissions, and flow field in an industrial swirl-stabilized burner at different acoustic boundary conditions (short and long combustor). The pilot injector is moved coaxially to three mounting positions from the burner underside to the burner dump plane, the same as the fluidics. Type of injection (fuel only, air and fuel premixed, and air only) as well as shape and mounting position (burner bottom, middle, and top) of the injector are investigated at a constant overall equivalence ratio. The injection of air transferred from the main tubes through the pilot lance shows better results than the pilot fuel and premixed pilot injection. The stability as well as lower NOx emissions is achieved by transferring less than 10% of the main air flow through the pilot. The suppression of the instabilities of those two different combustion chambers is achieved at lean combustion. At different coaxial locations, the transferred air is generally able to perform the stability while the best results are achieved when the injector is located at zero position. PIV measurements performed downstream of the burner show that the pilot injection has a strong impact on the mean flow field at the flame stability locations. The strong pilot air momentum increases the mixing of fuel and air, helps in flame stabilization outside of the burner, and prevents flame oscillation which is one source of thermoacoustic instabilities in the present combustor. The results also show an increase in the flow velocity at the reacting conditions due to the faster motion of the hot spots than in the cold flow. Velocity magnitudes in the conical jet as well as in the recirculation zone increase as a consequence of the heat released by the flame. The corner vortices change in size depending on the pilot momentum. The cone angle in the reacting flow changes because of the buoyancy effect. The last part is concerned with the changes of swirling flow which can be strongly influenced by the outlet conditions of the combustion chamber, especially at subcritical flow conditions. The effect of such changes on the mean flow or coherent structures is still unclear. It is investigated in the present work in an industrial swirl inducing burner in cold flow conditions with help of PIV technique. Proper orthogonal decomposition (POD) as well as acoustic measurements was used to characterize the coherent structures shed from the burner mouth. The combustor length (8.17 D and 24.63 D) and the outlet area contraction ratio (1, 0.56, 0.27, and 0.09) are varied. Major changes in the flow field are achieved when using the short combustor and the smallest contraction ratio. For this case, a central jet with streamwise velocity is added to the typical central recirculation zone. The POD analysis of the contraction ratios 1 and 0.09 for the long combustor shows that the first helical mode as well as Kelvin Helmholtz vortices are present with minor changes for both cases. At a contraction ratio of 0.09, some new structures at the jet location and near the combustor wall appeared. Measurements techniques used in non-reacting and reacting flow investigations are acoustic measurements with a microphone, hydrophone, PIV, LIF, Hot Wire, temperature measuring with thermocouple, gas analysis, and OH* chemiluminescence photography with camera.
URI: urn:nbn:de:kobv:83-opus-32436
http://depositonce.tu-berlin.de/handle/11303/3261
http://dx.doi.org/10.14279/depositonce-2964
Exam Date: 28-Sep-2011
Issue Date: 17-Oct-2011
Date Available: 17-Oct-2011
DDC Class: 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
Subject(s): Acoustic geometry
EV Burner
Fluidics
Pilot
Acoustic geometry
EV Burner
Fluidics
Pilot
Usage rights: Terms of German Copyright Law
Appears in Collections:Technische Universität Berlin » Fakultäten & Zentralinstitute » Fakultät 5 Verkehrs- und Maschinensysteme » Institut für Strömungsmechanik und Technische Akustik (ISTA) » Publications

Files in This Item:
File Description SizeFormat 
Dokument_59.pdf32.04 MBAdobe PDFThumbnail
View/Open


Items in DepositOnce are protected by copyright, with all rights reserved, unless otherwise indicated.