Download or read book Effects of Curvature and Dilution on Unsteady Premixed Laminar Flame Propagation written by K. Kailasanath and published by . This book was released on 1985 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have used a time-dependent, one-dimensional, Lagrangian model to study laminar flames in stoichiometric hydrogen-oxygen mixtures diluted with nitrogen. For stoichiometric hydrogen-air mixtures we have seen that spherically expanding flame first decelerates until the velocity reaches a minimum value, and then it accelerates. For large radii, the burning velocity approaches the planar burning velocity. These same trends are also observed as the amount of diluent is increased. With increasing dilution, the flames reach their minimum velocities at larger times and larger radii. These observations are explained on the basis of flame stretch. The spherical geometry results are compared to be results from another set of calculations in planar flame in the same mixture. In both planar and spherical geometries, the effect of increasing the dilution is to lower the burning velocities. Since the burning velocity is smaller in the spherical geometry, the flame is less than that of a planar flame in the same mixture. In both planar and spherical geometries, the effect of increasing the dilution is to lower the burning velocities. Since the burning velocity is smaller in the spherical geometry, the flame can be extinguished (or quenched) with less dilution in the spherical geometry than in the planar geometry. We also discuss the implications of these results to laminar flame quenching and flammability limits. (Author).
Download or read book Effect of Equivalence Ratio on Premixed Flame Response to Unsteady Strain rate and Curvature written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The detailed dynamical response of flames in turbulent reacting flow involves a complex interaction between unsteady flow structures and flame chemistry. Two essential features of this interaction are the unsteady strain-rate and curvature disturbances to the reaction zone. In this work, the authors focus on a single flow length/time scale feature in two dimensions (2D), and its effect on a premixed flame for a range of mixture conditions. In particular, they study the interaction of a premixed freely propagating methane-air flame with a 2D counter-rotating vortex pair in an unbounded domain. In earlier work, they studied this flow using C[sub 1] kinetics, at stoichiometric conditions. Notable observations include the shift of the reaction zone into the products on the vortex-pair centerline, leading to depletion of H, O and OH, and the consequent general drop in reaction rates on the centerline flame segment. Curvature-induced focusing/defocusing effects were observed at the positively curved flame cusp, leading to modifications in internal transport fluxes of various species and radicals in the flame, and associated effects on H production and fuel consumption rates. These results were extended to more detailed kinetics, using other C[sub 1] and C[sub 2] mechanisms, which demonstrated the effect of choice of chemical mechanism on the observed transient flame response. The present study focuses on the dependence of the transient flame response on reactants mixture equivalence ratio. Two reactants mixture conditions are studied: case 1 is a stoichiometric conditions - equivalence ratio[Phi]= 1.0, and case 2 is rich at[Phi]= 1.2. In both cases, the reactants are 20% N[sub 2]-diluted.
Download or read book Effects of Diluents on Laminar Premixed Hydrogen Flames in Microgravity written by Li Qiao and published by . This book was released on 2007 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Research Abstracts written by and published by . This book was released on 1986 with total page 876 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1986 with total page 1162 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Low Gravity Fluid Dynamics and Transport Phenomena written by Robert L. Sani and published by AIAA. This book was released on 1990 with total page 786 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 1988 with total page 872 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Government Reports Announcements Index written by and published by . This book was released on 1996 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Studies of Curvature Strain and Unsteady Effects on Premixed Flames written by Tarek Echekki and published by . This book was released on 1992 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dynamics of Reactive Systems Flames and configurations written by J. Raymond Bowen and published by . This book was released on 1986 with total page 448 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 Microgravity Combustion Science written by and published by . This book was released on 1989 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Chemical and Physical Processes in Combustion written by Combustion Institute (U.S.). Eastern States Section. Fall Technical Meeting and published by . This book was released on 1996 with total page 558 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Microgravity Science and Applications Bibliography written by United States. Office of Space Science and Applications and published by . This book was released on 1989 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt:
