Author: S. M. CorreaPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Local Extinction Mechanisms in Non-premixed Turbulent Combustion
Author: S. M. CorreaLocal Extinction and Reignition in Turbulent Nonpremixed Combustion
Author: Paiboon SripakagornPublisher:
ISBN:
Category : Combustion
Languages : en
Pages : 212
Book Description
Scientific and Technical Aerospace Reports
Author: Experimental Studies of Turbulent Local Extinction
Author: Marc SchneiderKinematic Study of the Evolution and Properties of Flame Surfaces in Turbulent Nonpremixed Combustion with Local Extinction and Reignition
Author: Weirong WangPublisher:
ISBN:
Category : Combustion
Languages : en
Pages : 206
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.
Turbulent Combustion
Author: Norbert PetersPublisher: Cambridge University Press
ISBN: 1139428063
Category : Science
Languages : en
Pages : 322
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.
Turbulent Premixed Flames
Author: Nedunchezhian SwaminathanPublisher: Cambridge University Press
ISBN: 1139498584
Category : Technology & Engineering
Languages : en
Pages : 447
Book Description
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.
Detection of Local Extinction and Re-ignition in Non-premixed Ethylene-air Flames Using Chemical Explosive Mode Analysis
Author: Cong LiTurbulent Combustion Modeling
Author: Tarek EchekkiPublisher: Springer Science & Business Media
ISBN: 9400704127
Category : Technology & Engineering
Languages : en
Pages : 496
Book Description
Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.
Advanced Turbulent Combustion Physics and Applications
Author: N. SwaminathanPublisher: Cambridge University Press
ISBN: 1108497969
Category : Science
Languages : en
Pages : 485
Book Description
Explore a thorough overview of the current knowledge, developments and outstanding challenges in turbulent combustion and application.