Reduction of Combustion Noise and Instabilities Using Porous Inert Material with a Swirl-stabilized Burner PDF Download
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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: 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: 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: Joseph Warren Meadows
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 191
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Book Description
Study of combustion dynamics has gained significant research attention since low-emission systems are increasingly employed in the industry. In particular, combustion noise and thermo-acoustic instabilities are of great importance in highly critical applications such as power generation, jet propulsion engines, and rocket propulsion systems. Recently, porous inert media (PIM), also referred to as foam insert, has shown promise in mitigating combustion noise and thermo-acoustic instabilities in lean premixed (LPM), swirl-stabilized combustion at atmospheric pressure and elevated pressures. In this study, the flow field without and with PIM is investigated to understand the underlying mechanisms responsible for mitigating thermo-acoustic instabilities. Experiments are conducted for LPM combustion and lean direct injection (LDI) combustion. First, time-resolved PIV technique is utilized to measure the non-reacting flow field without and with PIM. Although the flow field inside the annulus of the foam insert was optically inaccessible, measurements immediately downstream provide insight into the instantaneous flow field and turbulence characteristics. The study highlights the role of the foam insert on vorticity, velocity, shear layer spreading angle, recirculation zone dynamics, and turbulent kinetic energy; which ultimately affects the acoustics behavior of the combustor in a favorable manner. The effect of PIM on the dominant turbulent structures in the flow field is quantified using proper orthogonal decomposition (POD) technique. Next, flow field measurements are acquired for LPM swirl-stabilized combustion without and with PIM. The turbulent structures similar to the non-reacting flow field are also present in the reacting flow field, with notable difference in size and shape. The instantaneous and average flow fields provide insight into the effects of PIM on the velocity and turbulence fields. POD analysis is used to quantify the effect of PIM on the dominant turbulent structures, and PIM is shown to distribute the turbulent energy from the large scale structures to smaller scale structures. By harmonically reconstructing the flow field at the frequency of thermo-acoustic instability, the feedback mechanism is found to be the vortical structures in the corner recirculation zones, and PIM is shown to eliminate the feedback mechanism. The efficacy of PIM in mitigating combustion noise and thermo-acoustic instabilities is demonstrated for liquid fuel combustion utilizing the LDI concept. In this system, the flame stabilizes downstream of the dump plane due to a balance of flow velocity and flame speed of the fuel-air mixture created upstream. The ring shaped PIM is placed at the dump plane of the combustor to alter the flow field in an advantageous manner. Sound pressure levels (SPL) and CO and NOx emissions are measured for combustion without and with PIM inserts. Effect of atomizing air to liquid mass ratio on SPL suggests equivalence ratio oscillations are the driving force for thermo-acoustic instabilities. Results show that the PIM insert reduces broad band combustion noise, mitigates peak instabilities occurring at the first longitudinal mode of the natural frequency of the combustor, and facilitates thermal feedback from the flame to the fuel atomization process. Different insert geometries were examined and they all reduced SPLs, but the converging foam geometry provided the best performance. Finally, flow fields of LDI combustion are experimentally measured using time-resolved PIV technique without and with PIM. The instantaneous flow field highlights the role of PIM on the fluctuating velocity field. The driving mechanism for thermo-acoustic instability is identified by analyzing the fluctuating flow field, and PIM is found to decrease the driving force for thermo-acoustic instability. The average flow field is used to show the effect of PIM on the turbulence and POD analysis is used to quantify the effect of PIM on the turbulent structures. The study identifies spatial and temporal non-homogeneities in equivalence ratio as the feedback mechanisms for exciting thermo-acoustic instabilities in LDI swirl-stabilized combustion. In general, PIM decreases the driving force while increasing the dampening force in both LPM and LDI combustion systems.
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: 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: Victor Manuel Rodriguez Martinez
Publisher:
ISBN:
Category : Combustion engineering
Languages : en
Pages : 564
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Book Description
Author: Christian O. Paschereit
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: S. Murugappan
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Miron Semenovich Natanzon
Publisher: AIAA (American Institute of Aeronautics & Astronautics)
ISBN:
Category : Science
Languages : en
Pages : 298
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Book Description
First published in 1986 by Mashinostroenie, Moscow.
Author: Zachary Alexander LaBry
Publisher:
ISBN:
Category :
Languages : en
Pages : 87
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Book Description
Thermoacoustic or combustion instability, a positive feedback loop coupling heat release rate and acoustic oscillations in a combustor, is one of the greatest challenges currently facing the development of new gas turbine systems for propulsion and power generation. Traditional gas turbine designs have bypassed the problem of combustion instability by designing non-premixed combustors around a fixed operating point. Increasing trends toward lower emissions and greater fuel flexibility have placed more emphasis on developing lean-premixed combustors that are stable over a range of operating conditions. This thesis explores two aspects of combustion instability in the context of a swirl-stabilized, lean-premixed combustor: the role of the major coherent flow structures, and the potential for using secondary air injection to passively suppress combustion instability. Microjets inject air into the combustion chamber in the flame anchoring zone. These microjet injectors attempt to modify the flow field so as to break the feedback mechanism between the chamber acoustics and the heat release rate. Eight microjet injector configurations are studied. Flow is injected axially into the outer recirculation zone or radially into the inner recirculation zone. The injectors inject air with either no swirl, the same swirl direction as the main air flow, or the opposite swirl direction as the main air flow. Chamber acoustics are measured using sensitive microphones. The flame and flow field are interrogated using high-speed imaging and stereoscopic particle image velocimetry. The bulk of this work was conducted for lean propane/air flames, slightly above the lean blowoff limit. Two modes of instability were examined: the 1/4 wave mode at 40 Hz, and the 3/4 wave mode at 105 Hz. Without microjet injection, the combustor transitions directly from the 1/4 wave mode instability to the 3/4 wave mode instability as the equivalence ratio is increased above 0.58. Counter-swirling radial microjets injecting air into the inner recirculation zone increased the lower limit of the 3/4 wave mode to an equivalence ratio of 0.62 and reduced the amplitude of the 1/4 wave mode, effectively creating a stable operating regime for equivalence ratios between the two modes. Microjet injector tests indicate that the inner recirculation zone has a dominant role in the dynamic stabilization of the flame. This observation is confirmed by stereoscopic PIV measurements that reveal periodic formation and collapse of the vortex breakdown bubble in the 3/4 wave mode and vortex shedding in the inner recirculation zone in the 1/4 wave mode.
