Local Extinction Mechanisms in Non-premixed Turbulent Combustion PDF Download
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Author: S. M. Correa
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: S. M. Correa
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Paiboon Sripakagorn
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 212
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Author:
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Category : Aeronautics
Languages : en
Pages : 1572
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Author: Marc Schneider
Publisher:
ISBN:
Category :
Languages : en
Pages : 264
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Author: Weirong Wang
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 206
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Book Description
Turbulent nonpremixed combustion with local extinction and reignition is an important fundamental phenomenon that has many practical implications. The objective of the research reported in this thesis is to identify and understand the mechanisms that govern extinction and reignition by studying the kinematics of the stoichiometric mixture fraction isosurface (i.e., the flame surface). The configuration, area and the behavior of the flame surface can quantitatively describe the interaction of the flame with turbulent flow and thus the flame surface kinematics has a strong influence on the properties of the reactive scalars. One particular property of importance is the mean flame surface density [signma]. This study contributes to the determination of [sigma] by proposing three approaches for its measurement through the use of direct numerical simulations (DNS) data for the case of incompressible and isotropic turbulence. These direct and indirect approaches proposed for the computation and modeling of the time evolution of [sigma] are 1) direct numerical measurement, 2) theoretical prediction from the concept of level crossings with the application of Rice's theorem\cite{S.O.Rice1}, which leads to 3) two separate modeling approaches using statistical definitions and by balance equation of isoscalar surface area density. These approaches allow us to follow the growth of the surface due to local surface stretching by turbulence and its ultimate decrease due to molecular destruction. The statistical model fairly accurately predicts the evolution of [sigma]. We are also able to determine values of the principal terms in the evolution equation for [sigma], including the surface stretching term and the molecular destruction term. We find that the stretching and destruction term are approximately statistically independent of the isoscalar value of the surface. The difficulties in modeling of local flame extinction and reignition are demonstrated by evaluating the application of the steady-state flamelet (SFL) model. The transient effects (i.e., the lag of flame quenching behind fluctuations in the stoichiometric scalar dissipation rate X[subscript st] ) and the time lag of reignition relative to the relaxation of X[subscript st] are not considered by the SFL model. These are demonstrated by showing the mixing and reactive quantities along the stoichiometric mixture fraction contour lines. With the knowledge of the flame surface evolution and its properties, the mechanisms of local extinction and reignition can be directly investigated by the dynamics of flame hole (i.e., an extinguished flame surface) expansion and collapse. The flame surface is first resolved as a mesh of triangular surfaces within the three-dimensional DNS volume that represents the stoichiometric surface. A criterion is developed on this flame surface mesh to identify instantaneously local quenched regions and distinguish these from burning surface regions. Next, a new methodology is developed to numerically identify contiguous extinguished stoichiometric surface elements such that the size of a single flame hole can be identified. The new methodology is tested and found to be accurate. This numerical algorithm can provide rich geometric information on local flame hole structure and along with knowledge of the local reacting properties for each individual flame hole. The statistics of the geometric properties of the flame holes are then obtained. During the reignition process, the area size distribution of flame holes was found to be roughly invariant with time which results in an approximate time invariant average hole area. This appears to be due to the loss of small flame holes with time while larger holes become smaller. To first order, this process appears to approximate a self-preserving size distribution.
Author: Norbert Peters
Publisher: Cambridge University Press
ISBN: 1139428063
Category : Science
Languages : en
Pages : 322
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Book Description
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.
Author: N. Swaminathan
Publisher: Cambridge University Press
ISBN: 1108497969
Category : Science
Languages : en
Pages : 485
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Book Description
Explore a thorough overview of the current knowledge, developments and outstanding challenges in turbulent combustion and application.
Author: Cong Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Kenneth Kuan-yun Kuo
Publisher: John Wiley & Sons
ISBN: 111809929X
Category : Science
Languages : en
Pages : 914
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Book Description
Detailed coverage of advanced combustion topics from the author of Principles of combustion, Second Edition Turbulence, turbulent combustion, and multiphase reacting flows have become major research topics in recent decades due to their application across diverse fields, including energy, environment, propulsion, transportation, industrial safety, and nanotechnology. Most of the knowledge accumulated from this research has never been published in book form—until now. Fundamentals of Turbulent and Multiphase Combustion presents up-to-date, integrated coverage of the fundamentals of turbulence, combustion, and multiphase phenomena along with useful experimental techniques, including non-intrusive, laser-based measurement techniques, providing a firm background in both contemporary and classical approaches. Beginning with two full chapters on laminar premixed and non-premixed flames, this book takes a multiphase approach, beginning with more common topics and moving on to higher-level applications. In addition, Fundamentals of Turbulent and Multiphase Combustion: Addresses seven basic topical areas in combustion and multiphase flows, including laminar premixed and non-premixed flames, theory of turbulence, turbulent premixed and non-premixed flames, and multiphase flows Covers spray atomization and combustion, solid-propellant combustion, homogeneous propellants, nitramines, reacting boundary-layer flows, single energetic particle combustion, and granular bed combustion Provides experimental setups and results whenever appropriate Supported with a large number of examples and problems as well as a solutions manual, Fundamentals of Turbulent and Multiphase Combustion is an important resource for professional engineers and researchers as well as graduate students in mechanical, chemical, and aerospace engineering.
Author: S. M. Correa
Publisher:
ISBN:
Category :
Languages : en
Pages : 77
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Book Description
The goal of this program is to understand turbulence chemistry interactions in combustion up to and including localized extinction. Experimentally, pilot stabilized non premixed turbulent jet flames of selected mixtures are being studied under conditions conducive to strain-induced local extinction. Laser based techniques such as Raman scattering and Rayleigh scattering are employed. Analytically, models based on the asymptotically thin flamelet concept and on distributed reaction zone concepts are being assessed. A significant finding is that the popular contemporary view of a turbulent flame as an ensemble of asymptotically thin flamelets seems incorrect. Alternative mechanisms based on thick flamelets are proposed. The results include: (1) A complete re evaluation of Raman data showing significant corrections due to high temperature effects. Keywords: Turbulence chemistry interactions, Extinction, Blowoff, turbulent diffusion flames, Superequilibrium, Laser diagnostics.
