Download or read book Flame Extinction Dynamics of Lean Premixed Bluff body Stabilized Flames written by Marissa Kelley MacDonald and published by . This book was released on 2014 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mechanisms of Flame Extinction for Bluff Body Stabilized Flames with Influences of Pressure Gradient Tailoring written by Anthony J. Morales and published by . This book was released on 2018 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame extinction continues to hinder the performance of combustion technologies used in propulsion systems and power generating turbomachinery. Within these applications, there is a crucial need to improve energy output while minimizing harmful environmental impacts. Lean combustion helps attain these goals by minimizing fuel costs and reducing NO[subscript x] emissions. However, operating at lean conditions increases the likelihood of flame extinction; the flame becomes more susceptible to hydrodynamic instabilities which can induce global blowout and termination of the combustion process. The work in this thesis is focused on identifying the mechanisms of flame extinction and controlling these mechanisms via pressure gradient tailoring. This is accomplished within a premixed blow-down combustion facility utilizing a bluff body flame stabilizer where flame extinction is induced by removing the flow of fuel into the reactant mixture. CH* chemiluminescence imaging and high-speed particle imaging velocimetry (PIV) are used to determine the flame boundary and resolve the reacting flow field, respectively. The mechanisms of flame extinction are attributed to the changing vorticity dynamics within the flow field as the equivalence ratio is reduced, which will directly influence the strain rate experienced by the flame. To influence these vorticity dynamics, the test section walls are manipulated to alter the downstream pressure gradients. It is determined that increasing the magnitude of the downstream pressure gradient increases the growth of the strain rate and vorticity experienced by the flame.
Download or read book Advances in Turbulent Combustion Dynamics Simulations in Bluff Body Stabilized Flames written by Jonathan Michael Tovar and published by . This book was released on 2015 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work examines the three main aspects of bluff-body stabilized flames: stationary combustion, lean blow-out, and thermo-acoustic instabilities. For the cases of stationary combustion and lean blow-out, an improved version of the Linear Eddy Model approach is used, while in the case of thermo-acoustic instabilities, the effect of boundary conditions on the predictions are studied. The improved version couples the Linear Eddy Model with the full-set of resolved scale Large Eddy Simulation equations for continuity, momentum, energy, and species transport. In traditional implementations the species equations are generally solved using a Lagrangian method which has some significant limitations. The novelty in this work is that the Eulerian species concentration equations are solved at the resolved scale and the Linear Eddy Model is strictly used to close the species production term. In this work, the improved Linear Eddy Model approach is applied to predict the flame properties inside the Volvo rig and it is shown to over-predict the flame temperature and normalized velocity when compared to experimental data using a premixed single step global propane reaction with an equivalence ratio of 0.65. The model is also applied to predict lean blow-out and is shown to predict a stable flame at an equivalence ratio of 0.5 when experiments achieve flame extinction at an equivalence ratio of 0.55. The improved Linear Eddy Model is, however, shown to be closer to experimental data than a comparable reactive flow simulation that uses laminar closure of the species source terms. The thermo-acoustic analysis is performed on a combustor rig designed at the Air Force Research Laboratory. The analysis is performed using a premixed single step global methane reaction for laminar reactive flow and shows that imposing a non-physical boundary condition at the rig exhaust will result in the suppression of acoustic content inside the domain and can alter the temperature contours in non-physical ways. It can be concluded from this work that it is important to include the proper exhaust configuration for reacting thermo-acoustic calculations so that non-physical boundary conditions do not compromise the solution.
Download or read book A Detailed Investigation of Bluff Body Stabilized Flames Postprint written by and published by . This book was released on 2007 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reduced Order Models (ROMs) and Computational Fluid Dynamics (CFD) codes are tools used to predict the extinction of flames behind bluff bodies. Accurate prediction of these models and codes is predicated on their validation with experimental data. This paper describes detailed experiments to obtain validation data for bluff body stabilized flames over a wide range of conditions. Included are non-reacting data from CFD and LDV, lean blowout and high speed images for three different flame holders. In our previous paper (Kiel 2006) it was asserted that the large vortices were a major driver of extinction. Those assertions are further supported here. It is concluded that the vortex dynamics and not geometry is the dominant mechanism for bluff body flame extinction. This conclusion is supported by the lean blowout data, by the high speed images and reference data from NACA.
Download or read book Investigation of Blowoff Mechanism and Forced Response of Bluff Body Stabilized Turbulent Premixed Flames written by Swetaprovo Chaudhuri and published by . This book was released on 2010 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lean Blowout Dynamics for Premixed Bluff body Flames written by Anthony J. Morales and published by . This book was released on 2020 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lean blowout is experimentally investigated for premixed bluff-body flames under various inlet velocity conditions, pressure gradients, and turbulence conditions to study the influence of fluid mechanics on the lean blowout process. A premixed combustion facility paired with a bluff-body flame stabilizer is used for the study. For all experiments, lean blowout is induced by temporally decreasing the fuel flow rate into the reactant stream. A suite of high-speed optical diagnostics are simultaneously employed to capture the transient blowout process: particle image velocimetry (PIV), stereoscopic PIV, and C2*/CH* chemiluminescence imaging. These diagnostics allow for the instantaneous flame boundary, velocity fields, equivalence ratios, and local flame strain rates to be evaluated during blowout. For all testing conditions, the results show that the blowout process is highly coupled to the fluid mechanics within the reacting domain and blowout is driven from flame-flow interactions (i.e. flame-vorticity interactions or flame-turbulence interactions). The results also demonstrate that altering the vorticity dynamics or turbulence conditions within the reacting domain can profoundly augment or attenuate the blowout process.
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 Stabilization of an Unconfined Flame by a Bluff Body written by Jean R. Hertzberg and published by . This book was released on 1986 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stabilization and Dynamic of Premixed Swirling Flames written by Paul Palies and published by Academic Press. This book was released on 2020-07-03 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work Addresses the challenges of turbulent combustion modeling with numerical simulations Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities Covers the design of a fully premixed injector for future jet engine applications
Download or read book LES of Bluff Body Stabilized Premixed and Partially Premixed Combustion written by Ionut Porumbel and published by VDM Publishing. This book was released on 2008 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main topic of this work is the study of the equivalence ratio effect on flame stability and dynamics in premixed and partially premixed flames by means of an LES algorithm able to handle the entire range of combustion regimes, with no ad-hoc adjustable parameters and able to respond automatically to variations in the inflow conditions.
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 An Introduction to Combustion written by Stephen R. Turns and published by McGraw-Hill Education. This book was released on 2012 with total page 732 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduction to Combustion is the leading combustion textbook for undergraduate and graduate students because of its easy-to-understand analyses of basic combustion concepts and its introduction of a wide variety of practical applications that motivate or relate to the various theoretical concepts. This is a text that is useful for junior/senior undergraduates or graduate students in mechanical engineering and practicing engineers. The third edition updates and adds topics related to protection of the environment, climate change, and energy use. Additionally, a new chapter is added on fuels due to the continued focus on conservation and energy independence.
Download or read book Blowoff Behavior of Bluff Body Stabilized Flames in Vitiated and Partially Premixed Flows written by Steven G. Tuttle and published by . This book was released on 2010 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigation on the Effects of Free Stream Turbulence and Fuel Type on Structure and Blowoff Characteristics of Turbulent Premixed Bluff body Stabilized Flames written by Bikram Roy Chowdhury and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation on the effect of different levels of turbulence intensity and properties of the fuel/air mixture on the structure and characteristics of lean flames stabilized on an axisymmetric bluff body is described in this thesis. Simultaneous imaging of hydroxyl (OH) and formaldehyde (CH2O) by planar laser induced fluorescence and particle image velocimetry (PIV) were used to study the interaction between the flame and the flow field. CH2O fluorescence and the pixel-by-pixel multiplication of OH and CH2O fluorescence signals were utilized to mark preheat and heat release regions respectively. In addition, high-speed chemiluminescence imaging was performed to understand the time resolved characteristics of the flame. The first part of the thesis focuses on the characteristics of stably burning lean methane/-, propane/- and ethylene/air flames when subjected to low (4 %), moderate (14 %) and intense (24 and 30%) levels of free stream turbulence. The flame front structure was observed to be strongly dependent on the free stream turbulence level of the incoming fuel/air mixture as well on the properties of the fuel/air mixture. Formation of cusps and unburnt mixture fingers were observed as the turbulence intensity was increased from 4 to 14 % but, the heat release region remained continuous. Under intense turbulence conditions, methane/- and ethylene/air (f = 0.85) flames exhibited localized extinctions along the flame sheet and flamelet merging events which created isolated pockets of reactants in the flame envelope. In addition to these features, propane/- and ethylene/air (f=0.655) flames exhibited the occurrence of flame fragmentation events and the general shape of these flames were observed to intermittently switch from a symmetric (varicose) to asymmetric (sinuous) mode. Several properties were measured to characterize the effects of turbulence – flame interaction which includes the average preheat and reaction zone thicknesses, strain rates and curvature along the flame front, burning fraction, flame brush thickness, flame surface density, area ratio and turbulent flame speed. The next part of the thesis focuses on blowoff dynamics of lean methane/-, propane/- and ethylene/air flames for mean velocities of 5, 10 and 15 m/s and subjected to free stream turbulence levels from 4 to 30%. Apart from the propane/air flames at an apporach velcoity of 5 m/s and turbulence intensity of 30 %, increasing turbulence intensity was found to reduce the flame stability. The blowoff equivalence ratios of propane/air flames was observed to be higher than methane/- and ethylene/air flames. As blowoff was approached, the flame front and shear layer vortices entangled inducing high local strain rates on the flame front that exceed the extinction strain rate resulting in significant breaks along the reaction zone. At conditions near blowoff, significant increase in the frequency of breaks along the reaction zone was observed for low and moderate turbulence conditions. For the higher turbulence conditions, fragmentation of the flame along with the presence of sinuous wakes was observed which aided in the penetration of reactants into the recirculation zone. Velocity vectors near the flame holes indicate the penetration of the reactants into the recirculation zone. Mostly similar sequence of events was observed for methane/-, propane/- and ethylene/air flames near blowoff. Several properties weremeasured to characterize the near blowoff flames which include the strain rate and curvature statistics along the flame front, burning fraction, asymmetric index and the average duration of the blowoff event. Based on the observation from the experiments, turbulent flame speed was attributed to be the primary factor in governing the blowoff equivalence ratio. This point of view was examined by comparing the mean strain rate of methane/- and ethylene/air flames at the equivalence ratio corresponding to near blowoff for propane/air flames.
Download or read book Turbulent Combustion Modeling written by Tarek Echekki and published by Springer Science & Business Media. This book was released on 2010-12-25 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Swirl stabilized Lean premixed Flame Combustion Dynamics An Experimental Investigation of Flame Stabilization Flame Dynamics and Combustion Instability Control Strategies written by Rajavasanth Rajasegar and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigation of the Dynamics and Blowoff Characteristics of Bluff body Stabilized 2D V Shaped Turbulent Premixed Flames with Different Gaseous Hydrocarbon Fuels written by Rishi Roy and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
