Download or read book Reduced Kinetic Mechanisms for Premixed Laminar Flames written by Weigang Wang and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reduced Kinetic Mechanisms for Applications in Combustion Systems written by Norbert Peters and published by Springer Science & Business Media. This book was released on 2008-09-11 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt: In general, combustion is a spatially three-dimensional, highly complex physi co-chemical process oftransient nature. Models are therefore needed that sim to such a degree that it becomes amenable plify a given combustion problem to theoretical or numerical analysis but that are not so restrictive as to distort the underlying physics or chemistry. In particular, in view of worldwide efforts to conserve energy and to control pollutant formation, models of combustion chemistry are needed that are sufficiently accurate to allow confident predic tions of flame structures. Reduced kinetic mechanisms, which are the topic of the present book, represent such combustion-chemistry models. Historically combustion chemistry was first described as a global one-step reaction in which fuel and oxidizer react to form a single product. Even when detailed mechanisms ofelementary reactions became available, empirical one step kinetic approximations were needed in order to make problems amenable to theoretical analysis. This situation began to change inthe early 1970s when computing facilities became more powerful and more widely available, thereby facilitating numerical analysis of relatively simple combustion problems, typi cally steady one-dimensional flames, with moderately detailed mechanisms of elementary reactions. However, even on the fastest and most powerful com puters available today, numerical simulations of, say, laminar, steady, three dimensional reacting flows with reasonably detailed and hence realistic ki netic mechanisms of elementary reactions are not possible.
Download or read book Reduced Kinetic Mechanisms and Asymptotic Approximations for Methane Air Flames written by Mitchell D. Smooke and published by Springer. This book was released on 2014-03-12 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this comprehensive text a systematic numerical and analytical treatment of the procedures for reducing complicated systems to a simplified reaction mechanism is presented. The results of applying the reduced reaction mechanism to a one-dimensional laminar flame are discussed. A set of premixed and non-premixed methane-air flames with simplified transport and skeletal chemistry are employed as test problems that are used later on to evaluate the results and assumptions in reduced reaction networks. The first four chapters form a short tutorial on the procedures used in formulating the test problems and in reducing reaction mechanisms by applying steady-state and partial-equilibrium approximations. The final six chapters discuss various aspects of the reduced chemistry problem for premixed and nonpremixed combustion.
Download or read book Reduced Kinetic Mechanisms and Asymptotic Approximations for Methane air Flames written by Mitchell D. Smooke and published by Springer. This book was released on 1991 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this comprehensive text a systematic numerical and analytical treatment of the procedures for reducing complicated systems to a simplified reaction mechanism is presented. The results of applying the reduced reaction mechanism to a one-dimensional laminar flame are discussed. A set of premixed and non-premixed methane-air flames with simplified transport and skeletal chemistry are employed as test problems that are used later on to evaluate the results and assumptions in reduced reaction networks. The first four chapters form a short tutorial on the procedures used in formulating the test problems and in reducing reaction mechanisms by applying steady-state and partial-equilibrium approximations. The final six chapters discuss various aspects of the reduced chemistry problem for premixed and nonpremixed combustion.
Download or read book Sensitivity Analysis of Laminar Premixed CH 4 air Flames Using Full and Reduced Kinetic Mechanisms written by Bernd Rogg and published by . This book was released on 1990 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Kinetic Mechanisms for Premixed Laminar Steady State Methane Air Flames written by T. P. Coffee and published by . This book was released on 1983 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: A number of kinetic schemes have been used to model premixed, laminar, one-dimensional methane/air flames. Seven such kinetic schemes, including two new models, are compared with one another and with experimental data. The two new models, one with 14 species and one with 20 species, both agree with the experimental data over a range of stoichiometries from lean to rich. All of the models show good agreement for lean to slightly rich flames. This does not validate any of the models, even for this limited range. Rather, it is shown that the quantities measured are fairly insensitive to much of the mechanism. Therefore, models with incorrect kinetics can agree with the experimental data. In particular, the contribution of the C2 species to methane combustion is examined. While these species are important, we conclude that there is insufficient data to determine quantitatively the effects of the C2 chemistry reactions.
Download or read book Evaluation of Reduced Kinetic Mechanisms in Numerical Simulations of Non premixed Flames written by Joshua S. Hsu and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Detailed and Reduced Kinetic Mechanisms in Low emission Combustion Processes written by Sylvie Honnet and published by Cuvillier Verlag. This book was released on 2007 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Kinetic Mechanisms for Premixed Laminar Steady State Hydrogen Nitrous Oxide Flames written by and published by . This book was released on 1986 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report pertains to the detailed kinetics governing premixed, laminar, one-dimensional hydrogen/nitrous oxide flames. The long range goal is to understand the kinetics governing propellant decomposition, where nitrogen chemistry is important. Hydrogen/nitrous oxide flames are the simplest case of a flame controlled by nitrogen chemistry. A model has been developed for premixed, laminar, one-dimensional hydrogen/nitrous oxide flames. Results have been compared with a range of experimental data. The present model roughly reproduces the data, but inaccuracies still exist. Sensitivity and screening analyses have been used to indicate the additional experimental data needed to improve the model. Keywords: Burning Velocity.
Download or read book Reduced Chemical Kinetic Models for Real Fuels and Computational Flame Diagnostics of Premixed Combustion written by Ji-Woong Park and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation investigates different approaches to developing efficient yet accurate real-fuel chemistry for multi-dimensional computational fluid dynamics (CFD) simulations and computational flame diagnostics for premixed combustion. First, reduced kinetic models of real fuels are systematically developed based on detailed mechanisms with a hybrid chemistry (HyChem) approach. A two-stage reduction is utilized including a directed relation graph (DRG) and sensitivity analysis followed by linearized quasi-steady state approximation (LQSSA). Comprehensive validations are performed in homogeneous and diffusive systems over wide parameter ranges, showing good agreement between reduced and detailed mechanisms. The second approach focuses on spark ignition (SI) engine applications where laminar flame speed (LFS) plays a crucial role. Typically, in SI-engines, combustion starts at relatively high pressure and temperature. However, most chemical mechanisms are not validated in LFS at such conditions due to the lack of experimental data. The tailoring methodology of a chemical mechanism is proposed to improve prediction of LFS at engine-relevant conditions. Rate coefficients of the selected reactions important to LFS are identified through sensitivity analysis and adjusted within their uncertainty limits to match calculated LFS to experiment-based empirical correlation. The developed tailored mechanism is utilized in 3D SI-engine simulations and improved predictions are observed compared with experimental data. Lastly, a computational flame diagnostic tool to identify the extinction state of premixed flames is developed based on the chemical explosive mode (CEM) analysis (CEMA). Counterflow twin premixed flames show two different extinction modes with increasing stretch due to reaction incompleteness (Mode I) and preferential diffusion effect (Mode II). In Mode I, increasing stretch pushes the flame front, identified as zero-crossing of CEM eigenvalue, toward the stagnation plane such that twin flames merge and form a hot spot approaching extinction. The extinction Mode I can be identified by the zero-crossing of the CEM eigenvalue at the stagnation plane. For Mode II, the extinction occurs away from the stagnation plane due to the combined effect of stretch and preferential diffusion. A new criterion is constructed to quantify the contribution of back-diffusion of heat and radicals to the CEM in the preheat zone. The CEMA-based criteria are then validated in wide ranges of operating conditions covering lean to rich mixtures, elevated inlet temperature and pressure conditions, and small to large real-fuels, showing that it can be used as a leading order indicator for premixed flame extinction.
Download or read book Incorporating Reduced Kinetic Mechanisms in Numerical Simulations of Nonpremixed Flames written by Joshua Sun-See Hsu and published by . This book was released on 2002 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Chemical Kinetic Mechanisms on Turbulent Combustion written by Salvador Badillo-Rios and published by . This book was released on 2020 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the effects of alternative chemical kinetic mechanisms in turbulent reactive flows is critical to the ability to accurately simulate combustion processes, especially in practical systems. Exploring such effects is not a trivial endeavor because turbulent reactive simulations can be costly, especially when Direct Numerical Simulations (DNS) are employed and/or for large parameter studies. In addition, detailed chemical kinetic mechanisms are often too large and impractical for incorporation in multi-dimensional transient flow field simulations. The large number of species and reactions, as well as the wide range of time scales, in the detailed chemical kinetics account for the computational cost in largescale combustion simulations. Currently, reduced mechanisms are developed under specific laminar flow conditions in which selected global properties of a flame (e.g., ignition delay time, laminar flame speed, adiabatic flame temperature) are matched to those of the original detailed mechanism. However, this imposes restrictions on the operating range and applicability of these reduced mechanisms. For example, in addition to the presence of turbulence, it cannot be guaranteed that these specific conditions will be met everywhere in the flowfield for non-premixed combustion. If turbulence is shown to affect the results from reduced models, then use of the model would become flow and regime specific. It may even be necessary to simulate each flow configuration with detailed chemical kinetic mechanisms before reduced models can be developed for that flow configuration. A better understanding of the sensitivities of turbulent reactive flow results is clearly needed to address these issues. The Chemical Explosive Mode Analysis (CEMA) appears to be an efficient computational diagnostic tool that may give insight into the the important species and reactions in a given flowfield, and to help to explain differences that various kinetic mechanisms may produce in a reactive flowfield. Thus, CEMA may have the potential to help in the development of reduced mechanisms. The objective of this dissertation is to gain insights into the influence of alternative chemical kinetics mechanisms on the results of turbulent combustion simulations and, specifically, the effects of these mechanisms under conditions representative of rocket injector applications. Methane-oxygen combustion simulations of a shear coaxial injection configuration are performed using several chemical kinetic mechanisms ranging from detailed, to skeletal, to reduced mechanisms. Multi-dimensional simulations of rocket injector flowfields are used to establish the underlying issues and motivate the studies. 0D and 1D simulations in concert with the the Chemical Explosive Mode Analysis (CEMA) procedure are then employed to develop insight into the important species and reactions involved to explain differences between the different kinetic mechanisms. Injector results reveal that it is important to establish grid convergence before making comparisons of reaction mechanisms. They also show that the skeletal FFCM1-21 chemical mechanism has time-step and spatial grid sensitivity compared to the detailed GRI-Mech 3.0 mechanism. Given that FFCM1-21 is a skeletal mechanism, the absence of certain species may be responsible for the sensitivity. The CEMA module is first validated with published hydrogen-air 1D premixed flame results. The CEMA method is then applied to a 0D homogeneous combustion problem to obtain insights about the important species and reactions in methane-oxygen combustion for various chemistry models relevant to the rocket injector problem described earlier. A gaseous methane-oxygen mixture is studied as well as mixtures with the addition of H and/or O radicals to simulate the effects of turbulent mixing of burnt gases with reactants. For these cases, a new detailed mechanism (FFCM-1) and a reduced version (FFCMY-12) are used to study the underlying sensitivities. It is found that there is poor prediction of the ignition delay by the reduced mechanism FFCMY-12 in the presence of radicals as compared with the full FFCM-1 mechanism. Trends seen in 0D results help to identify the important species and reactions necessary for a reduced mechanism to replicate important phenomena such as ignition. Because of this, there is confidence that 0D simulations with the CEMA implementation could also help in pinpointing the pertinent species and reactions and in identifying and determining what to examine in a large and more complex turbulent dataset.
Download or read book Studies on High Pressure and Unsteady Flame Phenomena written by Chung K. Law and published by . This book was released on 1993 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the present program is to study the structure and response of steady and unsteady laminar premixed and nonpremixed flames in reduced and elevated pressure environments through (a) non-intrusive experimentation, (b) computational simulation using detailed flame and kinetic codes, and (c) asymptotic analysis with reduced kinetic mechanisms. During the reporting period progress has been made in the following projects: (1) a theoretical and experimental study of unsteady diffusion flames; (2) a computational and experimental study of methane/air flames at elevated pressures; (3) an asymptotic analysis of the structure of methane/air premixed flames with reduced chemistry; (4) an asymptotic analyses of the extinction of laminar premixed flames with volumetric heat loss and chain mechanisms; and (5) asymptotic analyses of ignition in the supersonic laminar flat-plate boundary layer and mixng layer. A total of five reprints are appended.
Download or read book Soot Formation in Combustion written by Henning Bockhorn and published by Springer Science & Business Media. This book was released on 2013-03-08 with total page 595 pages. Available in PDF, EPUB and Kindle. Book excerpt: Soot Formation in Combustion represents an up-to-date overview. The contributions trace back to the 1991 Heidelberg symposium entitled "Mechanism and Models of Soot Formation" and have all been reedited by Prof. Bockhorn in close contact with the original authors. The book gives an easy introduction to the field for newcomers, and provides detailed treatments for the specialists. The following list of contents illustrates the topics under review:
Download or read book Reduced Kinetic Mechanisms for Wet CO Flames written by W. Wang and published by . This book was released on 1992 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reduced Kinetic Mechanisms and Their Numerical Treatment written by W. Wang and published by . This book was released on 1992 with total page 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.
