Download or read book The Effects of Differential Diffusion in Counter flow Premixed Flames with Dilution and Enrichment written by Ehsan Abbasi Atibeh and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The continued combustion of fossil fuels to fulfill global energy demand is being questioned because of the well-known problem of greenhouse-gas (GHG) emissions, which introduces new carbon, in the form of carbon dioxide, into the environment causing climate change. However, the inherent advantages of combustion-based engines, e.g., energy and power densities, make it hard for other power systems to compete; hence, a leading strategy is to avoid burning fossil fuels by using alternative renewable fuels, such as hydrogen and renewable biofuels. Adaptability with alternative renewable fuels that have variable compositions is referred to as fuel flexibility, which is an important parameter of next-generation combustor design. However, fuel flexibility significantly affects combustor operability properties, such as blowout, flashback, and dynamic stability, mainly due to variations in turbulent burning rates. Changing the fuel and oxidizing-gas mixture composition affects flame characteristics and burning rates through changing: (1) mixture reactivity, which is represented by unstretched laminar flame speed, and (2) mixture diffusivity, i.e., the diffusivity of the deficient reactant and diffusivity of heat. The disparity between thermal and mass diffusivities at the flame front is known as "differential diffusion", which causes stretch sensitivity, and thermal-diffusive instabilities, in flame-front propagation, and is represented by Lewis number, a ratio of thermal-to-mass diffusivities.This thesis investigates the effects of differential diffusion and stretch sensitivity on propagation, stabilization, and structure of lean turbulent premixed flames in the thin reaction zone regime. In the context of fuel flexibility, various fuels and oxidizer-inert mixtures are used to form mixtures with distinct effective Lewis numbers, through changing both fuel diffusivity and thermal diffusivity of the mixture. In these experiments, the unstretched laminar flame speed is kept constant during mixture dilution, and hydrogen enrichment of hydrocarbon flames, through changing the mixture equivalence ratio, in order to minimize the effects of chemistry. Furthermore, bulk-flow properties and the temperature boundary condition are kept constant; hence, the study highlights the effects of differential diffusion. The experiments are carried out using strained counter-flow flames, in order to study the effects of both components of the flame stretch, i.e., hydrodynamic strain and curvature. Local instantaneous statistics of various flame parameters within the imaged plane are quantified using high-speed particle image velocimetry (PIV) and Mie scattering flame tomography at various levels of turbulence intensity. These statistics include flame location, flame velocity, and flame-front topology, such as flame stretch, flame-front curvature, and flame surface area.The statistics of various parameters of turbulent flames with distinct effective Lewis number show that the effects of differential diffusion on the burning rates and the structure of turbulent premixed flames are important in highly turbulent flames in the thin reaction zone of combustion. Furthermore, these results are not dependent on the fuel or oxidizing-gas mixture and can be described fully by the effective Lewis number and turbulence intensity. In addition, at constant turbulence intensities, differential diffusion increases the burning rate of turbulent flames in thermo-diffusively unstable mixtures through two main mechanisms: (1) increasing the local flamelet displacement velocity, and (2) increasing the flame surface area. This thesis shows the need to advance the combustion theory to produce models that can capture the effects of differential diffusion for flames in real-world combustion systems, in order to predict the performance of future fuel-flexible combustors. The experimental results of this thesis provide a valuable dataset for the validation of such theories." --

Download or read book Hydrogen for Future Thermal Engines written by Efstathios-Al. Tingas and published by Springer Nature. This book was released on 2023-07-14 with total page 586 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explores the potential of hydrogen combustion in thermal engines and serves as a foundation for future research. Hydrogen, a well-established energy carrier, has been used in internal combustion engines for centuries, but despite progress and industry interest, hydrogen engines have yet to reach mass production. In light of recent efforts to combat climate change with clean energy and environmentally-friendly technologies, the use of hydrogen in thermal engines is gaining momentum. This book examines the unique challenges of hydrogen combustion due to its wide flammability limits, high auto-ignition temperature, and high diffusivity. It reviews current knowledge on the fundamental and practical aspects of hydrogen combustion and considers current developments and potential future advancement.

Download or read book Engineering Fluid Dynamics 2019 2020 written by Bjørn H. Hjertager and published by MDPI. This book was released on 2021-02-25 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the successful submissions to a Special Issue of Energies entitled “Engineering Fluid Dynamics 2019–2020”. The topic of engineering fluid dynamics includes both experimental and computational studies. Of special interest were submissions from the fields of mechanical, chemical, marine, safety, and energy engineering. We welcomed original research articles and review articles. After one-and-a-half years, 59 papers were submitted and 31 were accepted for publication. The average processing time was about 41 days. The authors had the following geographical distribution: China (15); Korea (7); Japan (3); Norway (2); Sweden (2); Vietnam (2); Australia (1); Denmark (1); Germany (1); Mexico (1); Poland (1); Saudi Arabia (1); USA (1); Serbia (1). Papers covered a wide range of topics including analysis of free-surface waves, bridge girders, gear boxes, hills, radiation heat transfer, spillways, turbulent flames, pipe flow, open channels, jets, combustion chambers, welding, sprinkler, slug flow, turbines, thermoelectric power generation, airfoils, bed formation, fires in tunnels, shell-and-tube heat exchangers, and pumps.

Download or read book Combined Effects of Dilution and Co flow on the Stability of Lifted Non premixed Gaseous Flames written by David Andrew Wilson and published by . This book was released on 2005 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: Keywords: dilution, co-flow, non-premixed flame, diffusion flame, combustion, flame stability.

Download or read book Effects of Differential Diffusion on the Mutual Annihilation of Two Premixed Hydrogen air Flames written by Bhargav Bindiganavile Ranganath and published by . This book was released on 2003 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: Keywords: mechanical engineering, flames, combustion.

Download or read book Hydrodynamic and Differential diffusion Effects on Premixed Flame Propagation written by Changrong Cui and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame propagation in gaseous mixtures generally involve two length scales: one scale is associated with the diffusion processes and characterizes the flame thickness, and the other scale is associated with the underlying flow field. When the hydrodynamic length is larger than the nominal flame thickness, the flame can be viewed as a surface of density discontinuity, advected and distorted by the flow. The analysis of the internal structure of the flame provides expressions for the flame speed and temperature and jump conditions for the velocities and pressure across the flame. The resulting hydrodynamical model is valid for flames of arbitrary shape propagating in general fluid flows, being laminar or turbulent. The present work extends earlier studies by adopting a curvilinear coordinate system attached to the flame front, thus presenting a formulation in coordinate-free form, using a two-reactant scheme thus allowing for mixtures whose compositions vary from lean to rich including stoichiometric conditions, using non-unity and general reaction orders in an attempt to mimic a wider range of reaction mechanisms, allowing all transport coefficients to depend arbitrarily on temperature in order to better represent actual experimental conditions, and incorporating volumetric heat losses which may often lead to flame extinction.

Download or read book The Structure and Extinction of Counterflow Flames written by Ishwar Kanwar Puri and published by . This book was released on 1987 with total page 560 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Combined Effects of Dilution and Co flow on the Stability of Lifted Non premixed Gaseous Flames written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This research documents experiments and analysis of turbulent, lifted, non-premixed diffusion flames in co-flow and with dilution with implications for the development and operation of biogas-fueled combustors. Fuels used in this study were methane and ethylene. The diluent used was nitrogen. General trends were observed in the liftoff and reattachment behavior as affected by dilution of the fuel stream. Initial liftoff velocity was observed to decrease linearly with dilution, while initial lift height behavior was bimodal. Reattachment conditions were similar in overall behavior to liftoff conditions. Co-flow effects were not included in liftoff and reattachment studies. Combined effects of dilution and co-flow were also studied. Stabilization height compared to radial stabilization was found to be bimodal, with behavior differing in the potential core region compared with the far-field region. Dilution was found to decrease the radial stabilization distance, and co-flow tended to increase the radial stabilization distance. However, both effects were minor. The major results involve heat release effects. For given stabilization heights, stabilization velocity was found to decrease with dilution faster than laminar burning velocity with dilution. Stabilization height was also found to increase rapidly with dilution beyond a certain diluent concentration. Flames were also found to taper inward and become more cylindrical in shape as dilution increases. Implications for several flame stabilization theories are discussed. Future work for confirming the results of this research are also discussed.

Download or read book The Extinction and Structure of Counterflow Premixed Flames written by Jesse Keith Crump and published by . This book was released on 1989 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Boundary Layer Analyses of Differential Diffusion Effects In Laminar Jet Diffusion Flames written by Akhil Nekkanti and published by . This book was released on 2018 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical and numerical studies of laminar jet diffusion flames have been conducted in the limit of infinitely fast chemistry for unity oxygen Lewis number LO = 1, providing information on flame shapes and flame temperatures for different reactant-feed dilution, fuel Lewis number LF, and coflow-to-jet velocity ratios U0. Shvab-Zel'dovich coupling functions are used to write the conservation equations for planar and axisymmetric jet flames in the boundary-layer approximation. Specific consideration is given to the mixing-layer solution near the injector rim, where differential-diffusion effects are seen to result in the expected superadiabatic/subadiabatic temperature for LF smaller/larger than 1. These effects are more pronounced for U0 = 0 and at intermediate values of Zs. The evolution of the temperature along the flame is found to exhibit an unexpected behavior, in that irrespective of the dilution and coflow velocity the flame temperature always transitions from superadiabatic to subadiabatic when LF 1 and from subadiabatic to superadiabatic for LF 1. The variation with LF of the flame shape relative to the enthalpy eld is reasoned as the cause for the observed transition. Additional computations are performed for inverse diffusion flames with LO = 1 and LF ~= 1. These do not exhibit reversed differential-diffusion behaviors, indicating that the diffusivity of the abundant (co-flow) reactant is less critical than that of the deficient (central-jet) reactant.

Download or read book Effects of Differential Diffusion on the Mutual Annihilation of Two Premixed Hydrogen Air Flames written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The unsteady process of head on quenching of two laminar premixed hydrogen-air flames in one-dimension by mutual annihilation is investigated numerically using a detailed chemical mechanism and realistic transport. The process of annihilation through interactions is inevitable in highly corrugated turbulent flames, and contributes to turbulent flame shortening. Processes leading to mutual annihilation involve interactions that take place in the following stages: (1) interaction of preheat zones, which corresponds to the transport of heat and reactants, (2) interactions of the reaction layers as the flames merge, and finally (3) the process of burnout. The primary objective of this work is to study the effects of differential diffusion during the various events that occur during the unsteady process of annihilation. For the stoichiometric condition two cases are considered namely; a case where transport is based on prescribing non-unity Lewis numbers for all the species and a case with unity Lewis numbers prescribed for all the species. The latter case provides with a reference problem for the other flames considered. Because of the importance of differential diffusion during thermo-diffusive interactions, which are owed to the transport properties of H2, relative to temperature and the oxidizer, two additional cases are considered. They correspond to lean and rich hydrogen-air flames. The results show that differential diffusion of H2 plays an important role in determining the composition of the reacting mixture and thus, affects the final temperature and composition of the products. The differential diffusion of H2 causes a deficiency of the fuel for the stoichiometric and lean cases thereby altering the rates of reactions involving H2 while merger. For the rich case the deficiency caused by the differential diffusion is offset by the presence of excess H2 in the reaction mixture. Due to these conditions for the rich flames and non-unity Lewis number case for the s.

Download or read book Turbulent Combustion written by Norbert Peters and published by Cambridge University Press. This book was released on 2000-08-15 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.

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:

Download or read book Study on Oxygen enriched Laminar Counterflow Diffusion Flames written by Andrea Luigi Beltrame and published by . This book was released on 2000 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Transition to Renewable Energy Systems written by Detlef Stolten and published by John Wiley & Sons. This book was released on 2013-05-13 with total page 882 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this ready reference, top academic researchers, industry players and government officers join forces to develop commercial concepts for the transition from current nuclear or fossil fuel-based energy to renewable energy systems within a limited time span. They take into account the latest science and technology, including an analysis of the feasibility and impact on the environment, economy and society. In so doing, they discuss such complex topics as electrical and gas grids, fossil power plants and energy storage technologies. The contributions also include robust, conceivable and breakthrough technologies that will be viable and implementable by 2020.

Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

Download or read book Mathematical Modeling in Combustion and Related Topics written by Claude-Michel Brauner and published by Springer Science & Business Media. This book was released on 1988-03-31 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains invited lectures and contributed papers presented at the NATO Advanced Research Workshop on Mathematical Modeling in Combustion and related topics, held in. Lyon (France), April 27 - 30, 1987. This conference was planned to fit in with the two-month visit of Professor G.S.S. Ludford to the Ecole Centrale de Lyon. He kindly agreed to chair the Scientific and Organizing Committee and actively helped to initiate the meeting. His death in December 1986 is an enormous loss to the scientific community in general, and in particular, to the people involved in the present enterprise. The subject of mathematical modeling in combustion is too large for a single conference, and the selection of topics re flects both areas of recent research activity and areas of in terest to Professor G.S.S. Ludford, to whose memory the Advanced Workshop and this present volume are dedicated. The meeting was divided into seven specialized sessions detonation theory, mathematical analysis, numerical treatment of combustion problems, flame theory, experimental and industrial aspects, complex chemistry, and turbulent combustion. It brought together researchers and engineers from University and Industry (see below the closing remarks of the workshop by Prof. N. Peters). The articles in this volume have been judged and accepted on their scientific quality, and language corrections may have been sacrificed in order to allow quick dissemination of knowledge to prevail.