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Author: Zachary A. Smith
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 244
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Book Description
Combustion noise and thermo-acoustic instability present a major area of concern for many industrial combustion applications, especially those operating under lean-premixed (LPM) conditions. While LPM combustion reduces thermal NOx by allowing operation at reduced flame temperatures, LPM flames are particularly susceptible to combustion noise and instability. While combustion noise and thermo-acoustic instability are distinctly different phenomena; both originate from the same source -- unsteady heat release in a turbulent flow field. Instabilities are self-excited and arise when energy from combustion is added to the system faster than energy is dissipated by heat transfer. In a typical swirl-stabilized combustor, flame is stabilized downstream of the dump plane and is sustained by central and corner recirculation zones. The present study combines porous inert media (PIM) assisted combustion with swirl-stabilized combustion to alter the combustor flow field in an advantageous manner. A ring-shaped PIM insert is placed directly at the dump plane to eliminate zones of intense turbulent fluctuations, thereby mitigating combustion noise at the source. With PIM, a central flame is confined within the annular void of the insert while a small portion of reactants flow through the PIM and stabilize on the downstream surface. Additionally, the porous insert provides acoustic damping and passive attenuation of pressure waves. This study is a preliminary step towards implementing the technique at elevated operating pressures, and eventually, liquid fuel combustors. Atmospheric combustion tests are conducted for a variety operating conditions to determine effectiveness of PIM to reduce combustion noise and instability. Parameters varied include air preheat temperature, air flow rate, equivalence ratio, and swirler axial location. Experiments are conducted with a high swirl angle, as opposed to previous experiments which used a lower swirl angle. For most conditions, PIM is shown to reduce total sound pressure level (SPL) in cases where instability is not intense. For all cases where instability is the dominant component of total SPL, PIM is extremely effective in eliminating instability. In these cases, total SPL is reduced by as much as 30 dB with PIM combustion. Furthermore, experiments show that no significant pressure drop penalty is incurred with porous media.
Author: Zachary A. Smith
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 244
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Book Description
Combustion noise and thermo-acoustic instability present a major area of concern for many industrial combustion applications, especially those operating under lean-premixed (LPM) conditions. While LPM combustion reduces thermal NOx by allowing operation at reduced flame temperatures, LPM flames are particularly susceptible to combustion noise and instability. While combustion noise and thermo-acoustic instability are distinctly different phenomena; both originate from the same source -- unsteady heat release in a turbulent flow field. Instabilities are self-excited and arise when energy from combustion is added to the system faster than energy is dissipated by heat transfer. In a typical swirl-stabilized combustor, flame is stabilized downstream of the dump plane and is sustained by central and corner recirculation zones. The present study combines porous inert media (PIM) assisted combustion with swirl-stabilized combustion to alter the combustor flow field in an advantageous manner. A ring-shaped PIM insert is placed directly at the dump plane to eliminate zones of intense turbulent fluctuations, thereby mitigating combustion noise at the source. With PIM, a central flame is confined within the annular void of the insert while a small portion of reactants flow through the PIM and stabilize on the downstream surface. Additionally, the porous insert provides acoustic damping and passive attenuation of pressure waves. This study is a preliminary step towards implementing the technique at elevated operating pressures, and eventually, liquid fuel combustors. Atmospheric combustion tests are conducted for a variety operating conditions to determine effectiveness of PIM to reduce combustion noise and instability. Parameters varied include air preheat temperature, air flow rate, equivalence ratio, and swirler axial location. Experiments are conducted with a high swirl angle, as opposed to previous experiments which used a lower swirl angle. For most conditions, PIM is shown to reduce total sound pressure level (SPL) in cases where instability is not intense. For all cases where instability is the dominant component of total SPL, PIM is extremely effective in eliminating instability. In these cases, total SPL is reduced by as much as 30 dB with PIM combustion. Furthermore, experiments show that no significant pressure drop penalty is incurred with porous media.
Author: Larry Justin Williams
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 190
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Book Description
Combustion instabilities have presented major problems in high-pressure, turbulent combustion systems for nearly a century, beginning with rocket propulsion systems. To enhance combustion efficiencies, other engines, such as gas turbines for power generation, operate at high pressures and reactant flow rates that are only small relative to those of rocket engine operation. The majority of power generation systems today extract energy from such efficient combustion processes. Recently, gas turbine engines, both power generation and propulsion platforms, are operated under very lean conditions to reduce flame temperatures and thus, emissions of the primary smog forming constituent, NOx. Extinction, flashback, blowoff, and autoignition pose challenges when operating at lean-premixed conditions. Flame stability at such lean conditions is problematic; thus, a swirled flow method is used to anchor and stabilize these flames. Intense turbulence, resulting from the pressure drop across flow swirlers, drives fluctuations in pressure and heat release rate. The feedback between pressure oscillations and heat release fluctuations in the reaction zone often drives resonant instabilities that propagate through the flow and surrounding structures. Such self-excited instabilities influence high rates of heat release in the reaction zone, which is located near the point of injection. Vibrations and high temperatures lead to the fatigue of injection components, instrumentation, and downstream turbine blades. A novel passive combustion noise control technique is experimentally investigated in the present study. The approach involves the mating of a porous inert material (PIM) with the inlet of a swirl-stabilized, lean-premixed combustor. The foam insert reduces turbulent intensities within the inner and outer recirculation zones of a common swirl-stabilized burner, thus reducing the amplitude of combustion driven instabilities. Experiments are conducted at high pressures, with high reactant flow rates and equivalence ratios. Results show that the ceramic foam insert is effective at mitigating combustion instabilities, suppressing combustion noise, and potentially, acoustic damping. The total sound pressure level for many of the cases investigated is reduced by 10 dB and greater. Furthermore, the approach can easily be retrofitted to commercial, industrial, and propulsion gas turbine combustion systems.
Author: Dan Zhao
Publisher: Academic Press
ISBN: 0323899188
Category : Technology & Engineering
Languages : en
Pages : 1145
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Book Description
Thermoacoustic Combustion Instability Control: Engineering Applications and Computer Codes provides a unique opportunity for researchers, students and engineers to access recent developments from technical, theoretical and engineering perspectives. The book is a compendium of the most recent advances in theoretical and computational modeling and the thermoacoustic instability phenomena associated with multi-dimensional computing methods and recent developments in signal-processing techniques. These include, but are not restricted to a real-time observer, proper orthogonal decomposition (POD), dynamic mode decomposition, Galerkin expansion, empirical mode decomposition, the Lattice Boltzmann method, and associated numerical and analytical approaches. The fundamental physics of thermoacoustic instability occurs in both macro- and micro-scale combustors. Practical methods for alleviating common problems are presented in the book with an analytical approach to arm readers with the tools they need to apply in their own industrial or research setting. Readers will benefit from practicing the worked examples and the training provided on computer coding for combustion technology to achieve useful results and simulations that advance their knowledge and research. Focuses on applications of theoretical and numerical modes with computer codes relevant to combustion technology Includes the most recent modeling and analytical developments motivated by empirical experimental observations in a highly visual way Provides self-contained chapters that include a comprehensive, introductory section that ensures any readers new to this topic are equipped with required technical terms
Author: Daniel E. Sequera
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 305
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Book Description
Combustion instabilities represent a major problem during operation of power generation systems that can lead to costly shutdown. Combustion instabilities are self excited large amplitude pressure oscillations caused by the coupling of unsteady heat release and acoustic modes of the combustor. These oscillations cause fluctuating mechanical loads and fluctuating heat transfer that can result in catastrophic premature failure of components. Combustion noise, a significant source of noise in gas turbines, can lead to combustion instabilities. Combustion noise and instabilities are different phenomena; however, they both occur due to unsteady heat release of turbulent flames that excites acoustic modes of the combustor. The instabilities self excite when flame adds energy to the acoustic field at a faster rate than it can dissipate it. Swirl-stabilized combustion and porous inert medium (PIM) combustion are two methods that have extensively been used, although independently, for flame stabilization. In this study, the two concepts are combined so that PIM serves as a passive device to mitigate combustion noise and instabilities. A PIM insert is placed within the lean premixed, swirl-stabilized combustor to affect the turbulent flow field reducing combustion noise. This study is the first step for eventual implementation in liquid fuel systems. After presenting the concept, a numerical investigation of the changes in the mean flow field caused by the PIM is presented. Changes in the flow field can be beneficial for noise reduction by optimizing the geometric parameters of the PIM. Next, atmospheric pressure experiments were conducted at low reactant inlet velocity (
Author: Nitesh P. Yelve
Publisher: CRC Press
ISBN: 1040020828
Category : Technology & Engineering
Languages : en
Pages : 109
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Book Description
Vibration Engineering presents recent developments in the field of engineering, encompassing industrial norms, applications within the finite element method, infrastructure safety assessment, and active vibration control strategies. It offers a study in seismic vibration control and analysis for building structures and liquid storage tanks. Spanning across the multiple domains of vibration engineering, the book highlights machinery diagnostics, modal analysis, energy harvesting, balancing, vibration isolation, and human-vibration interaction. It discusses experimental fault identification in journal bearings using vibration-based methods. This book also considers advances in vibration-based structural health monitoring of civil infrastructures. This book will be a useful reference for industry professionals and engineers facing challenges while dealing with the vibrations in the fields of mechanical, aerospace, structural, and civil engineering.
Author: Avandelino Santana Jr.
Publisher: LAP Lambert Academic Publishing
ISBN: 9783838369921
Category :
Languages : en
Pages : 172
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Book Description
Combustion instability problems have been experienced during nearly every rocket engine development program, characterized by pressure oscillations and release of energy. Several distinct types of instability have been observed, including the high frequency instability or acoustic instability, which is usually suppressed by means of passive control devices. The main purpose of this work was the experimental investigation of Helmholtz resonators and baffles to control acoustic instabilities in combustion chambers. Firstly, cold tests were carried out on full-scale model to analyze the efficiency of resonators. Experimental frequency spectrum data, in excellent agreement with theory, demonstrated the resonator is capable to reduce significantly the SPL amplitude. Afterwards, results of hot tests were compared with cold tests and with theory. The experimental data validated the methodology to design resonators useable to control combustion instabilities. This book provides a step-by-step procedure, which can be helpful to engineers and designers of liquid rocket engines, rocket motors and industrial burners, or anyone else who has already faced acoustic instability problems.
Author: Anna Schwarz
Publisher: Springer Science & Business Media
ISBN: 3642020380
Category : Technology & Engineering
Languages : en
Pages : 304
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Book Description
November, 2008 Anna Schwarz, Johannes Janicka In the last thirty years noise emission has developed into a topic of increasing importance to society and economy. In ?elds such as air, road and rail traf?c, the control of noise emissions and development of associated noise-reduction techno- gies is a central requirement for social acceptance and economical competitiveness. The noise emission of combustion systems is a major part of the task of noise - duction. The following aspects motivate research: • Modern combustion chambers in technical combustion systems with low pol- tion exhausts are 5 - 8 dB louder compared to their predecessors. In the ope- tional state the noise pressure levels achieved can even be 10-15 dB louder. • High capacity torches in the chemical industry are usually placed at ground level because of the reasons of noise emissions instead of being placed at a height suitable for safety and security. • For airplanes the combustion emissions become a more and more important topic. The combustion instability and noise issues are one major obstacle for the introduction of green technologies as lean fuel combustion and premixed burners in aero-engines. The direct and indirect contribution of combustion noise to the overall core noise is still under discussion. However, it is clear that the core noise besides the fan tone will become an important noise source in future aero-engine designs. To further reduce the jet noise, geared ultra high bypass ratio fans are driven by only a few highly loaded turbine stages.
Author: Xiaoling Chen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This dissertation examines the model-based optimization of sensor placement, estimation, and control for the active suppression of thermoacoustic instabilities in a one-dimensional combustor. This research is motivated by the increasing use of lean premixed combustion for emission reduction in gas turbine combustors. Thermoacoustic instability is a potentially damaging side effect of lean premixed combustion, caused by the unstable coupling between acoustics and unsteady heat release. There is extensive existing literature on the suppression of this instability, using both passive means such as Helmholtz resonators and active stability control. Much of the work on active combustion stability control relies on the injection of an additional acoustic excitation or fuel supply to break the above undesirable unstable coupling, thereby suppressing instability. Researchers have shown the promise of active combustion instability control both in simulations and laboratory experiments, for both single and multiple modes of instability. Active combustion stability control remains relatively scarce in industrial practice, despite the rich existing literature indicating its potential for success. Several important research questions need to be answered in order to help bridge this gap. First, while much of the recent research on active combustion stability control assumes one-dimensional combustion dynamics, an open question remains regarding the importance of other dynamic effects in the combustor, such as the dynamic interactions between multiple flames. Second, the degree to which the placement of sensors and actuators in a combustor affects the accuracy with which combustion instability dynamics can be estimated remains relatively unexplored in the literature. Third, the suitability of traditional linear model-based estimation and control techniques for stabilizing combustion instabilities with nonlinear heat release dynamics also remains relatively unexplored in the literature. The overarching goal of this dissertation is to address the above gaps using a combination of optimal sensor placement, optimal estimation, and optimal control. Towards this goal, the dissertation makes six specific contributions to the literature: 1. First, the author performs an experimental comparison between thermoacoustic instabilities in single- versus multi-nozzle combustion systems (Chapter 2). This study shows that the dynamic interactions between multiple flames in a multi-nozzle combustor have a non-trivial impact on thermoacoustic instability, especially the time scales of the transient instabilities. This helps characterize and understand the constraints on the practical applicability of one-dimensional combustion instability models for multi-nozzle systems, including the models used in the remainder of this dissertation. 2. Second, the author optimizes the design of a laboratory characterization experiment for a one-dimensional combustor (Chapter 3). This optimization utilizes Fisher information analysis for optimal combustion instability characterization, for the first time. 3. Third, the dissertation shows, using a mix of simulation-based and experimental studies, that the above use of optimal experimental design improves combustion instability parameterization accuracy (Chapter 4). Moreover, by furnishing more accurate combustion instability models, one is able to achieve higher levels of confidence in the robustness of the resulting combustion stability controllers. 4. Fourth, the dissertation presents a novel algorithm that makes it possible to estimate combustion heat release rates from multi-microphone measurements of the resulting acoustic signatures, in a manner that does not require the modeling of heat release dynamics (Chapter 5). This is important because it simplifies the online estimation of heat release dynamics, compared to model-based estimation methods requiring a heat release model. 5. Fifth, the dissertation studies the impact of sensor placement on the observability and LQG control of combustion instabilities governed by a linear $n-\tau$ heat release model (Chapter 6). This work highlights the importance of placing acoustic sensors at specific locations like the pressure mode anti-node points, including the acoustically closed combustor boundary. 6. Finally, the author develops a computational framework for the co-simulation of linear combustor acoustics, model-based combustion stability control, and nonlinear heat release dynamics governed by a level-set solver (Chapter 7). To the best of the author's knowledge, this is the first framework in the literature enabling the simulation-based study of the efficacy of linear control for combustion instabilities characterized by nonlinear heat release dynamics. In making the above contributions to the literature, this dissertation builds on the well-established idea that linear model-based estimation and control can be effective in suppressing combustion instability. The novelty of the dissertation lies in: 1. Pushing the above idea further by examining the degree to which its efficacy can be enhanced further through the use of information theory to optimize sensor placement and experimental design for estimation/control applications. 2. Building a framework that makes it possible to study the efficacy of model-based linear estimation/control in the context of thermo-acoustic instabilities driven by nonlinear heat release dynamics.
Author: Richard Steinert
Publisher: Springer
ISBN: 3658138238
Category : Technology & Engineering
Languages : en
Pages : 52
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Book Description
In experiments on a prototypical combustor, Richard Steinert identifies new insights on the impact of noise on the phenomenon known as thermoacoustic instability. The phenomenon is a concerning issue which creates a technical limit on the efficiency and environmental impact of fossil fuels combustion in industrial combustors. It poses a threat to the structural integrity of practical systems such as gas turbine combustors and rocket engines. The experiments demonstrate that thermoacoustic systems feature an interesting noise-induced behaviour known as coherence resonance – a coherent response of dynamical systems close to their stability boundary that is induced by stochastic excitation. The work contained in this publication is an example illustrating the importance of fundamental considerations in solving perplexing engineering issues.
Author: Emmanuel Motheau
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Virtually all combustion chambers are subject to instabilities. Consequently there is a need to better understand them so as to control them. A possibility is to simulate the reactive flow within a combustor with the Large-Eddy Simulation (LES) method. However LES results come at a tremendous computational cost. Another route is to reduce the complexity of the problem to a simple thermoacoustic Helmholtz wave equation, which can be solved in the frequency domain as an eigenvalue problem. The coupling between the flame and the acoustics is then taken into account via proper models. The main drawback of this latter methodology is that it relies on the zero-Mach number assumption. Hence all phenomena inherent to mean flow effects are neglected. The present thesis aims to provide a novel strategy to introduce back some mean flow effects within the zero-Mach number framework. In a first part, the proper way to impose high-speed elements such as a turbine is investigated. The second part focuses on the coupling between acoustics and temperature heterogeneities that are naturally generated at the flame and convected downstream by the flow. Such phenomenon is important because it is responsible for indirect combustion noise that may drive a thermoacoustic instability. A Delayed Entropy Coupled Boundary Condition (DECBC) is then derived in order to account for this latter mechanism in the framework of a Helmholtz solver where the baseline flow is assumed at rest. In the last part, a realistic aero-engine combustor that features a mixed acoustic/entropy instability is studied. The methodology developed in the present thesis is tested and compared to LES computations. It is shown that computations with the Helmholtz solver can reproduce a complex combustion instability, and that this latter methodology is a potential tool to design new combustors so as to predict and avoid combustion instabilities.
