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 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 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 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 Fluid Mechanics Aspects of Fire and Smoke Dynamics in Enclosures written by Bart Merci and published by CRC Press. This book was released on 2022-10-24 with total page 355 pages. Available in PDF, EPUB and Kindle. Book excerpt: - written by world leading experts in the field - contains many worked-out examples, taken from daily life fire related practical problems - covers the entire range from basics up to state-of-the-art computer simulations of fire and smoke related fluid mechanics aspects, including the effect of water - provides extensive treatment of the interaction of water sprays with a fire-driven flow - contains a chapter on CFD (Computational Fluid Dynamics), the increasingly popular calculation method in the field of fire safety science
Download or read book Hydrodynamic Effects on Soot Formation in Laminar Hydrocarbon fueled Diffusion Flames written by Guozheng Lin and published by . This book was released on 1996 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advanced Thermodynamics for Engineers written by D. Winterbone and published by Butterworth-Heinemann. This book was released on 1996-11-01 with total page 399 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the basic theories of thermodynamics are adequately covered by a number of existing texts, there is little literature that addresses more advanced topics. In this comprehensive work the author redresses this balance, drawing on his twenty-five years of experience of teaching thermodynamics at undergraduate and postgraduate level, to produce a definitive text to cover thoroughly, advanced syllabuses. The book introduces the basic concepts which apply over the whole range of new technologies, considering: a new approach to cycles, enabling their irreversibility to be taken into account; a detailed study of combustion to show how the chemical energy in a fuel is converted into thermal energy and emissions; an analysis of fuel cells to give an understanding of the direct conversion of chemical energy to electrical power; a detailed study of property relationships to enable more sophisticated analyses to be made of both high and low temperature plant and irreversible thermodynamics, whose principles might hold a key to new ways of efficiently covering energy to power (e.g. solar energy, fuel cells). Worked examples are included in most of the chapters, followed by exercises with solutions. By developing thermodynamics from an explicitly equilibrium perspective, showing how all systems attempt to reach a state of equilibrium, and the effects of these systems when they cannot, the result is an unparalleled insight into the more advanced considerations when converting any form of energy into power, that will prove invaluable to students and professional engineers of all disciplines.
Download or read book Fundamentals of Premixed Turbulent Combustion written by Andrei Lipatnikov and published by CRC Press. This book was released on 2012-10-24 with total page 548 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lean burning of premixed gases is considered to be a promising combustion technology for future clean and highly efficient gas turbine combustors. Yet researchers face several challenges in dealing with premixed turbulent combustion, from its nonlinear multiscale nature and the impact of local phenomena to the multitude of competing models. Filling
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 Combustion Waves and Fronts in Flows written by Paul Clavin and published by Cambridge University Press. This book was released on 2016-07-28 with total page 723 pages. Available in PDF, EPUB and Kindle. Book excerpt: A self-contained presentation of the dynamics of nonlinear waves in combustion and other non-equilibrium energetic systems for students and specialists.
Download or read book A Gallery of Combustion and Fire written by Charles E. Baukal, Jr. and published by Cambridge University Press. This book was released on 2020-09-03 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Gallery of Combustion and Fire is the first book to provide a graphical perspective of the extremely visual phenomenon of combustion in full color. It is designed primarily to be used in parallel with, and supplement existing combustion textbooks that are usually in black and white, making it a challenge to visualize such a graphic phenomenon. Each image includes a description of how it was generated, which is detailed enough for the expert but simple enough for the novice. Processes range from small scale academic flames up to full scale industrial flames under a wide range of conditions such as low and normal gravity, atmospheric to high pressures, actual and simulated flames, and controlled and uncontrolled flames. Containing over 500 color images, with over 230 contributors from over 75 organizations, this volume is a valuable asset for experts and novices alike.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1973 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of Differential Diffusion Effects in Turbulent Hydrogen Jet Flame Using Conditional Moment Closure Method written by Man Ching Ma and published by . This book was released on 2014 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of differential diffusion in the numerical modelling of a turbulent non-premixed hydrogen-air jet flame using a Conditional Moment Closure (CMC) method are investigated. The CMC calculations, which are coupled with computational fluid dynamics (CFD) calculations, relax the commonly used assumption of equal species mass diffusivities. The focus is on the predictions of species mass fractions and temperatures, especially the production of NO. The results of the calculations are compared with available experimental measurements. The formulation of the CMC species transport equation including differential diffusion is presented and the closure of the terms are discussed. Further, the CMC equation for conditional enthalpy is also derived in the present study. The implementation of the CMC equations using two dimensional finite volume method is discussed, including a presentation of the discretised forms of the equations. The results of the CMC calculations including the effects of differential diffusion show that NO mass fractions are increased from the large underpredictions observed for equal diffusivity results near the jet nozzle. Improvements are also found for other species such as H2 and H2O. The results show physical behaviours, such as a shift in the location of the reaction zone and increased reaction rates due to increased diffusion rates of H2. It is also found that differential diffusion effects persist downstream from the nozzle, where the effects are expected to be small, and reasons for the discrepancies are discussed in the present study. The profiles obtained from the CMC calculations show large radial variations, much larger than in equal diffusivity calculations. An analysis isolating the differential diffusion effects of various species shows that the largest changes occur due to the accounting for the differential diffusivity of H2. A budget of the terms in the CMC equations for the differentially diffusing chemical species and enthalpy is also investigated.
Download or read book Unsteady Combustor Physics written by Tim C. Lieuwen and published by Cambridge University Press. This book was released on 2012-08-27 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing clean, sustainable energy systems is a pre-eminent issue of our time. Most projections indicate that combustion-based energy conversion systems will continue to be the predominant approach for the majority of our energy usage. Unsteady combustor issues present the key challenge associated with the development of clean, high-efficiency combustion systems such as those used for power generation, heating or propulsion applications. This comprehensive study is unique, treating the subject in a systematic manner. Although this book focuses on unsteady combusting flows, it places particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics and acoustic disciplines. Individuals with a background in fluid mechanics and combustion will find this book to be an incomparable study that synthesises these fields into a coherent understanding of the intrinsically unsteady processes in combustors.
Download or read book Solution of Strained Edge Flames by a Boundary Value Method written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 692 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.
