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Dynamic Stability Blowoff And Flame Characteristics Of Oxy Fuel Combustion
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Book Synopsis Dynamic Stability, Blowoff, and Flame Characteristics of Oxy-fuel Combustion by : Andrew Philip Shroll
Download or read book Dynamic Stability, Blowoff, and Flame Characteristics of Oxy-fuel Combustion written by Andrew Philip Shroll and published by . This book was released on 2011 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxy-fuel combustion is a promising technology to implement carbon capture and sequestration for energy conversion to electricity in power plants that burn fossil fuels. In oxy-fuel combustion, air separation is used to burn fuel in oxygen to easily obtain a pure stream of carbon dioxide from the products of combustion. A diluent, typically carbon dioxide, is recycled from the exhaust to mitigate temperature. This substitution of carbon dioxide with the nitrogen in air alters the thermodynamics, transport properties, and relative importance of chemical pathways of the reacting mixture, impacting the flame temperature and stability of the combustion process. In this thesis, methane oxy-combustion flames are studied for relevance to natural gas. First, a numerical 1-D strained flame shows significantly reduced consumption speeds for oxy-combustion compared to air combustion at the same adiabatic flame temperature. Competition for the H radical from the presence of carbon dioxide causes high CO emissions. Elevated strain rates also cause incomplete combustion in oxy-combustion, demonstrated by the effect of Lewis number with a value greater than one for flame temperatures under 1900 K. Most of this work focuses on experimental results from premixed flames in a 50 kW axi-symmetric swirl-stabilized combustor. Combustion instabilities, upon which much effort is expended to avoid in gas turbines with low pollutant emissions, are described as a baseline for the given combustor geometry using overall sound pressure level maps and chemiluminescence images of 1/4, 3/4, and 5/4 wave mode limit cycles. These oxy-combustion results are compared to conventional air combustion, and the collapse of mode transitions with temperature for a given Reynolds number is found. Hysteresis effects in mode transition are important and similar for air and oxy-combustion. Blowoff trends are also analyzed. While oxy-combustion flames blow off at a higher temperature for a given Reynolds number due to weaker flames, there is an unexpected negative slope in blowoff velocity vs temperature for both air and oxy-combustion. The blowoff data are shown to collapse due to blowoff velocity being inversely proportional to the molar heat capacities of the burned gas mixtures at a given power. Finally, particle image velocimetry results are discussed to relate flow structures to corresponding flame structures.
Book Synopsis Dynamics, Stability and Scaling of Turbulent Methane Oxy-combustion by : Nadim Walid Chakroun
Download or read book Dynamics, Stability and Scaling of Turbulent Methane Oxy-combustion written by Nadim Walid Chakroun and published by . This book was released on 2018 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon capture and storage (CCS) is an important strategy for reducing CO2 emissions, with oxy-fuel combustion being one of the most promising technologies because of it is high efficiency and low cost. In oxy-combustion, CH4/O2/CO2 mixtures burn at low temperatures (~~1700 K), high pressures (~~40 bar), where laminar burning velocities are about 7 times lower than in traditional CH4 /Air mixtures. Thus oxy-fuel combustors are more prone to blowoff and dynamic instabilities. In this thesis we examine turbulent oxy-combustion flame stabilization physics at the large and small scales using experimental studies and numerical simulations. Experimental measurements are used to establish the stability characteristics of flame macrostructures in a swirl stabilized combustor. We show that the transition in the flame macrostructure to a flame stabilized along both the inner and outer shear layers (Flame IV), scales according to the extinction strain rate, similar to air flames. To achieve accurate scaling, extinction strain rates must be computed at the thermal conditions of the outer shear layer, emphasizing the role of heat interactions with the wall boundary layer. Care must be exercised while modeling the chemical structure of oxy-flames. We show that the kinetics of CO2 (used as a diluent in oxy-combustion) is important in determining the consumption speed and flame extinction strain rate. Specifically, the extinction strain rate was found to be heavily impacted by the reaction CO2+ H -->/
Book Synopsis Investigation on Flame Characteristics and Burner Operability Issues of Oxy-Fuel Combustion by :
Download or read book Investigation on Flame Characteristics and Burner Operability Issues of Oxy-Fuel Combustion written by and published by . This book was released on 2013 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxy-fuel combustion has been used previously in a wide range of industrial applications. Oxy- combustion is carried out by burning a hydrocarbon fuel with oxygen instead of air. Flames burning in this configuration achieve higher flame temperatures which present opportunities for significant efficiency improvements and direct capture of CO2 from the exhaust stream. In an effort to better understand and characterize the fundamental flame characteristics of oxy-fuel combustion this research presents the experimental measurements of flame stability of various oxyfuel flames. Effects of H2 concentration, fuel composition, exhaust gas recirculation ratio, firing inputs, and burner diameters on the flame stability of these fuels are discussed. Effects of exhaust gas recirculation i.e. CO2 and H2O (steam) acting as diluents on burner operability are also presented. The roles of firing input on flame stability are then analyzed. For this study it was observed that many oxy-flames did not stabilize without exhaust gas recirculation due to their higher burning velocities. In addition, the stability regime of all compositions was observed to decrease as the burner diameter increased. A flashback model is also presented, using the critical velocity gradient gF) values for CH4-O2-CO2 flames. The second part of the study focuses on the experimental measurements of the flow field characteristics of premixed CH4/21%O2/79%N2 and CH4/38%O2/72%CO2 mixtures at constant firing input of 7.5 kW, constant, equivalence ratio of 0.8, constant swirl number of 0.92 and constant Reynolds Numbers. These measurements were taken in a swirl stabilized combustor at atmospheric pressure. The flow field visualization using Particle Imaging Velocimetry (PIV) technique is implemented to make a better understanding of the turbulence characteristics of CH4/air and CH4/38%O2/72%CO2 combustion. The velocity fluctuations, turbulence intensities and local propagation velocities along the combustion chamber have been determined. The turbulent intensities increase as we move away from the combustor axis. CH4-38%O2-72%CO2 flames have low radial velocity and turbulent intensity distributions at different axial distances when compared with CH4-Air flames.
Book Synopsis Investigation on Flame Characteristics of Oxy-fuel Combustion by : Md. Rafiqul Islam
Download or read book Investigation on Flame Characteristics of Oxy-fuel Combustion written by Md. Rafiqul Islam and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Approaches for Clean Combustion in Gas Turbines by : Medhat A. Nemitallah
Download or read book Approaches for Clean Combustion in Gas Turbines written by Medhat A. Nemitallah and published by Springer Nature. This book was released on 2020-03-24 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the development of novel combustion approaches and burner designs for clean power generation in gas turbines. It shows the reader how to control the release of pollutants to the environment in an effort to reduce global warming. After an introduction to global warming issues and clean power production for gas turbine applications, subsequent chapters address premixed combustion, burner designs for clean power generation, gas turbine performance, and insights on gas turbine operability. Given its scope, the book can be used as a textbook for graduate-level courses on clean combustion, or as a reference book to accompany compact courses for mechanical engineers and young researchers around the world.
Book Synopsis MILD Combustion: Modelling Challenges, Experimental Configurations and Diagnostic Tools by : Alessandro Parente
Download or read book MILD Combustion: Modelling Challenges, Experimental Configurations and Diagnostic Tools written by Alessandro Parente and published by Frontiers Media SA. This book was released on 2021-11-26 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Unsteady Combustor Physics by : Tim C. Lieuwen
Download or read book Unsteady Combustor Physics written by Tim C. Lieuwen and published by Cambridge University Press. This book was released on 2012-08-27 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing clean, sustainable energy systems is a pre-eminent issue of our time. Most projections indicate that combustion-based energy conversion systems will continue to be the predominant approach for the majority of our energy usage. Unsteady combustor issues present the key challenge associated with the development of clean, high-efficiency combustion systems such as those used for power generation, heating or propulsion applications. This comprehensive study is unique, treating the subject in a systematic manner. Although this book focuses on unsteady combusting flows, it places particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics and acoustic disciplines. Individuals with a background in fluid mechanics and combustion will find this book to be an incomparable study that synthesises these fields into a coherent understanding of the intrinsically unsteady processes in combustors.
Book Synopsis Stability Limits of the Premixed Stoichiometric Cyanogen-oxygen Flame by : Irving Fruchtman
Download or read book Stability Limits of the Premixed Stoichiometric Cyanogen-oxygen Flame written by Irving Fruchtman and published by . This book was released on 1962 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Oxyfuel Combustion for Clean Energy Applications by : Medhat A. Nemitallah
Download or read book Oxyfuel Combustion for Clean Energy Applications written by Medhat A. Nemitallah and published by Springer. This book was released on 2019-02-11 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book aims to be the reference book in the area of oxyfuel combustion, covering the fundamentals, design considerations and current challenges in the field. Its first part provides an overview of the greenhouse gas emission problem and the current carbon capture and sequestration technologies. The second part introduces oxy-fuel combustion technologies with emphasis on system efficiency, combustion and emission characteristics, applications and related challenges. The third part focuses on the recent developments in ion transport membranes and their performance in both oxygen separation units and oxygen transport reactors (OTRs). The fourth part presents novel approaches for clean combustion in gas turbines and boilers. Computational modelling and optimization of combustion in gas turbine combustors and boiler furnaces are presented in the fifth part with some numerical results and detailed analyses.
Book Synopsis Oxygen-Enhanced Combustion by : Charles E. Baukal Jr.
Download or read book Oxygen-Enhanced Combustion written by Charles E. Baukal Jr. and published by CRC Press. This book was released on 2013-03-15 with total page 779 pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion technology has traditionally been dominated by air/fuel combustion. However, two developments have increased the significance of oxygen-enhanced combustion-new technologies that produce oxygen less expensively and the increased importance of environmental regulations. Advantages of oxygen-enhanced combustion include less pollutant emissi
Book Synopsis Effect of Variable Fuel Composition on Emissions and Lean Blowoff Stability Performance by : Andrés Colorado
Download or read book Effect of Variable Fuel Composition on Emissions and Lean Blowoff Stability Performance written by Andrés Colorado and published by . This book was released on 2017 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Technical Memorandum written by and published by . This book was released on 1991 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Thermoacoustic Combustion Instability Control by : Dan Zhao
Download or read book Thermoacoustic Combustion Instability Control written by Dan Zhao and published by Academic Press. This book was released on 2023-02-13 with total page 1145 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis Basic Considerations in the Combustion of Hydrocarbon Fuels with Air by : Lewis Flight Propulsion Laboratory. Propulsion Chemistry Division
Download or read book Basic Considerations in the Combustion of Hydrocarbon Fuels with Air written by Lewis Flight Propulsion Laboratory. Propulsion Chemistry Division and published by . This book was released on 1958 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Impact of Fuel and Oxidizer Composition on Premixed Flame Stabilization in Turbulent Swirling Flows by : Soufien Taamallah
Download or read book Impact of Fuel and Oxidizer Composition on Premixed Flame Stabilization in Turbulent Swirling Flows written by Soufien Taamallah and published by . This book was released on 2016 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: The world relies on fossil fuels as its main energy source (86.7% in 1973, 81.7% in 2012). Several factors including the abundance of resources and the existing infrastructure suggest that this is likely to continue in the near future (potentially 75% in 2040). Meanwhile climate change continues to be a pressing concern that calls for the development of low CO2 energy systems. Among the most promising approaches are pre-combustion capture technologies, e.g., coal gasification and natural gas reforming that produce hydrogen-rich fuels. Another approach is oxy-combustion in which air is replaced by a mixture of O2/CO2/H2O as the oxidizer stream. However, modern gas turbines have been optimized to operate on methane-air combustion and several challenges, notably thermo-acoustic instability, arise when using other fuels or oxidizers because of their different thermochemical and transport properties. While these phenomena constitute a major challenge under conventional operations, using hydrogen-rich fuels or CO2-rich oxidizer exacerbates the problem by modifying the combustor stability map in ways that are not well understood. In this thesis, we identify combustion modes most prone to dynamics, predict the onset of thermo-acoustic instability over a wide range of fuel and oxidizer compositions, and define parameters that can scale the data. To this end, a combination of experimental and numerical tools were deployed. We carried out a series of experiments in an optically accessible laboratory-scale swirl-stabilized combustor typical of those found in modern gas turbines, using high-speed chemiluminescence to examine the flame macrostructure; high-speed Particle Image Velocimetry and OH Planar Laser Induced Fluorescence to probe the flow and flame microstructure. Numerical simulations were used to complement experiments and examine the complex three-dimensional two-way interaction between the flame and the turbulent swirling flow. Experimental data were used to construct the stability maps for different CH4-H2 mixtures and analyze the dynamic flame macrostructures and their transitions. A comparison with acoustically uncoupled combustion shows that the onset of thermo-acoustic instability is concomitant with a specific transition associated with the intermittent appearance of the flame in the outer recirculation zone (ORZ) and stabilization along the outer shear layer (forming between the swirling jet and the ORZ, as revealed by the PIV-PLIF data). The sudden onset of large amplitude limit cycle oscillations and the observed hysteresis suggest the existence of a sub-critical Hopf bifurcation typically characterized by a bistable or "triggering" zone; the flame intermittency in the ORZ can potentially provide the disturbance required to trigger these oscillations. Using a dual-camera method to track chemiluminescence in space and time, this flame transition was found to originate from a reacting kernel that detaches from the inner shear layer flame (forming between the jet and the vortex breakdown zone), reaching the ORZ and spinning at a specific frequency; its characteristic Strouhal number is independent of the Reynolds number and the fuel/oxidizer, only a function of the swirl strength. We propose a new Karlovitz number based criterion that defines the transition on a flow time - flame time space, the former being the inverse of the spinning frequency and the latter being the flame extinction strain rate. According to this scaling, the flame survives in the ORZ if and when it can overcome the region's bulk strain rate. This criterion is valid over a wide range of operating, fuel and oxidizer composition, covering a wide range of fast to slow chemistry scenarios. Given the role of this flame transition in triggering the instability, the same criterion is applicable to predicting the onset of thermo-acoustics. The interaction of the turbulent swirling flow with the flame is further examined using large eddy simulations. Numerical simulations show that the experimentally observed large scale flame structures along the inner shear layer are due to a helical vortex core that originates at the swirler's centerbody. This vortical structure stays aligned with the centerline in the combustor upstream section, but bends and reaches the inner shear layer-stabilized flame around the sudden expansion where it causes the flame wrinkling. We propose that the flame kernel igniting the ORZ/ OSL observed in the experiment may be related to the interaction between the helical vortical structure and the outer shear layer.
Book Synopsis Lean Blowoff Characteristics of Swirling H2/co/ch4 Flames by : Qingguo Zhang
Download or read book Lean Blowoff Characteristics of Swirling H2/co/ch4 Flames written by Qingguo Zhang and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes an experimental investigation of lean blowoff for H2/CO/CH4 mixtures in a swirling combustor. This investigation consisted of three thrusts. The first thrust focused on correlations of the lean blowoff limits of H2/CO/CH4 mixtures under different test conditions. It was found that a classical Damköhler number approach with a diffusion correction could correlate blowoff sensitivities to fuel composition over a range of conditions. The second part of this thesis describes the qualitative flame dynamics near blowoff by systematically characterizing the blowoff phenomenology as a function of hydrogen level in the fuel. These near blowoff dynamics are very complex, and are influenced by both fluid mechanics and chemical kinetics; in particular, the role of thermal expansion across the flame and extinction strain rate were suggested to be critical in describing these influences. The third part of this thesis quantitatively analyzed strain characteristics in the vicinity of the attachment point of stable and near blowoff flames. Surprisingly, it was found that in this shear layer stabilized flame, flow deceleration is the key contributor to flame strain, with flow shear playing a relatively negligible role. Near the premixer exit, due to strong flow deceleration, the flame is negatively strained i.e., compressed. Moving downstream, the strain rate increases towards zero and then becomes positive, where flames are stretched. As the flame moves toward blowoff, holes begin to form in the flame sheet, with a progressively higher probability of occurrence as one moves downstream. It is suggested that new holes form with a more uniform probability, but that this behavior reflects the convection of flame holes downstream by the flow. It has been shown in prior studies, and affirmed in this work, that flames approach blowoff by first passing through a transient phase manifested by local extinction events and the appearance of holes on the flame. A key conclusion of this work is that the onset of this boundary occurs at a nearly constant extinction strain rate. As such, it is suggested that Damköhler number scalings do not describe blowoff itself, but rather the occurrence of this first stage of blowoff. Given the correspondence between this first stage and the actual blowoff event, this explains the success of classical Damköhler number scalings in describing blowoff, such as shown in the first thrust of this thesis. The physics process associated with the actual blowoff event is still unclear and remains a key task for future work.
Book Synopsis Experimental Investigation of the Dynamics and Blowoff Characteristics of Bluff-body Stabilized 2D, V-Shaped Turbulent Premixed Flames with Different Gaseous Hydrocarbon Fuels by : Rishi Roy
Download or read book Experimental Investigation of the Dynamics and Blowoff Characteristics of Bluff-body Stabilized 2D, V-Shaped Turbulent Premixed Flames with Different Gaseous Hydrocarbon Fuels written by Rishi Roy and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
