Download or read book Characterization of Fast Flames for Turbulence induced Deflagration to Detonation Transition written by Jessica Marcella Chambers and published by . This book was released on 2018 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, chemiluminescence, and Schlieren measurements. The investigation classifies the fast flame propagation modes at various regimes. The study further examines the conditions for a turbulent fast flame at the boundary of transitioning to quasi-detonation. The evolution of the flame-compressibility interactions for this turbulent fast flame is characterized. The local measured turbulent flame speed is found to be greater than the Chapman–Jouguet deflagration flame speed which categorizes the flame to be at the spontaneous transition regime and within the deflagration-to-detonation transition runaway process.

Download or read book Turbulence compressibility Dynamics of Fast Flames for Turbulence Induced Deflagration to detonation written by Jessica Chambers and published by . This book was released on 2021 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the fundamental mechanisms for detonation initiation is turbulence induced deflagration-to-detonation transition (tDDT). This research experimentally explores the dynamics of highly turbulent fast flames that are characterized by extremely high turbulent flame speeds, experience increased effects of compressibility, and may develop a runaway acceleration combined with a pressure buildup that leads to tDDT. The flame dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, OH* chemiluminescence, pressure measurements, and schlieren imaging. We study various regimes of fast flame propagation conditions for runaway acceleration of turbulent fast flames and effects of compressibility on the evolution of these flames. When the local measured turbulent flame speed is found to be greater than the Chapman-Jouguet deflagration speed, the flame is categorized to be at the runaway transition regime that eventually leads to a detonation.

Download or read book Compressibility Mechanisms of Turbulent Flames and Detonations written by Hardeo Chin and published by . This book was released on 2021 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: Propulsion systems are influenced by the efficiency of combustion systems. One approach to substantially improve combustion efficiency is through pressure gain combustion or detonation-based engines. Detonations exhibit attractive features such as increased stagnation pressure and rapid heat release; however, their highly unsteady and three-dimensional nature makes them difficult to characterize. In addition, the deflagration state prior to detonation is not well defined experimentally. Detonations can be achieved via the deflagration-to-detonation transition (DDT), where a deflagration that propagates on the order of 1 - 10 m/s is accelerated to a detonation that propagates on the order of 2000 m/s. The DDT process is highly dynamic and can occur through several mechanisms such as the Zeldovich reactivity-gradient mechanism where hot spots are created by Mach stem reflections, localized vorticial explosions, boundary layer effects, or turbulence. This work focuses on transient compressible flame regimes within the turbulent DDT (tDDT) process which causes a flame to undergo various burning modes. These burning modes can be categorized into four regimes: (1) slow deflagrations, (2) fast deflagrations, (3) shock-flame complex, and (4) detonation. To achieve each burning mode, turbulence levels and propagation velocities are tailored using perforated plates and various fuel-oxidizer compositions. The primary goal of this dissertation is to characterize the relationship between the turbulent flame speed (ST) and Chapman-Jouguet (CJ) deflagration speed (SCJ) using high-speed optical diagnostics in a turbulent shock tube facility. This work will: (1) further validate and classify the turbulence-compressibility characteristics associated with fast flames that lead to detonation onset in a highly turbulent environment, (2) quantify local ST for fast flames, and (3) investigate the flow field conditions of flame modes relating to the SCJ criteria, from slow deflagrations to shock-flame complexes.

Download or read book Flame generated Turbulence for Flame Acceleration and Detonation Transition written by Rachel Hytovick and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Detonations are a supersonic mode of combustion witnessed in a variety of applications, from next-generation propulsion devices to catastrophic explosions and the formation of supernovas. Detonations are typically initiated through the deflagration to detonation transition (DDT), a detailed process where a subsonic flame undergoes rapid acceleration increasing compressibility until a hotspot forms on the flame front inciting a detonation wave to form. Due to the complex nature of the phenomena, DDT is commonly investigated in three stages -- (i) preconditioning, (ii) detonation onset, and (iii) wave propagation and stability. The research presented explores each of these stages individually, with a focus on preconditioning, to further resolve the governing mechanisms needed to initiate and sustain a detonation. More specifically, this work seeks to investigate the flow field and flame characteristics in reactions with increasing compressibility. Additionally, the research examines detonation onset and wave propagation to attain an all-encompassing concept of the DDT process. The work uses simultaneous high-speed diagnostics, consisting of particle image velocimetry (PIV), OH* chemiluminescence, schlieren and pressure measurements, to experimentally examine the preconditioning stage. For detonation onset and propagation, megahertz diagnostics (OH* chemiluminescence and schlieren) are implemented to quantitatively visualize the supersonic event. Through the comprehensive suite of diagnostics, this research deduces the role of turbulence in detonation onset to an ongoing cycle of flame generated compression that amplifies until the hotspot ignites.

Download or read book Compressibility Effect on Turbulent Flames and Detonation Initiation and Propagation written by Jonathan Sosa and published by . This book was released on 2019 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.

Download or read book Major Research Topics in Combustion written by M.Y. Hussaini and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 668 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Institute for Computer Applications in Science and Engineer ing (ICASE) and NASA Langley Research Center (LaRC) brought together on October 2-4, 1989 experts in the various areas of com bustion with a view to expose them to some combustion problems of technological interest to LaRC and possibly foster interaction with the academic community in these research areas. The top ics chosen for this purpose were flame structure, flame stability, flame holding/extinction, chemical kinetics, turbulence-kinetics in teraction, transition to detonation, and reacting free shear layers. The lead paper set the stage by discussing the status and issues of supersonic combustion relevant to scramjet engine. Then the ex perts were called upon i) to review the current status of knowledge in the aforementioned ;:I. reas, ii) to focus on how this knowledge can be extended and applied to high-speed combustion, and iii) to suggest future directions of research in these areas. Each topic was then dealt with in a position paper followed by formal discussion papers and a general discussion involving the participants. The position papers discussed the state-of-the-art with an emphasis on key issues that needed to be resolved in the near future. The discussion papers crit ically examined these issues and filled in any lacunae therein. The edited versions of the general discussions in the form of questions from the audience and answers from the speakers are included wher ever possible to give the reader the flavor of the lively interactions that took place.

Download or read book Compressible Turbulent Flame Speed of Highly Turbulent Standing Flames written by Jonathan Sosa and published by . This book was released on 2018 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.

Download or read book Run Up Distance From Deflagration to Detonation In Fast Flames written by Mohamed Saifelislam Abdelgadir Ahmed and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the process of deflagration-to-detonation transition (DDT) in reactive gases, the flame typically accelerates first to the choked flame condition (known as a Chapman-Jouguet deflagration), where it propagates at the sound speed with respect to the product gases. Subsequently, the choked flame may transit to a detonation. In the present study, the transition length from choked flames to detonations was measured experimentally in laboratory-scale experiments in methane, ethane, ethylene, acetylene, and propane with oxygen as oxidizer. The choked flames were first generated following the quenching of an incident detonation after its interaction with cylindrical obstacles with two different blockage ratios, 75\% and 90\%. Comparison with a recently proposed model confirms that these are Chapman-Jouguet deflagrations. The subsequent acceleration was monitored via large-scale time-resolved shadowgraphy. The mechanism of transition was found to be through the amplification of transverse waves and hot spot ignition from local Mach reflections. The transition length was found to correlate very well with the mixture's sensitivity to temperature and pressure fluctuations. These fluctuations could be connected to a unique parameter (X), introduced by Radulescu. The parameter is the product of the non-dimensional activation energy (Ea/RT) and the ratio of chemical induction to reaction time (ti/tr). Mixtures with a higher X were found to be more prompt to hot spot ignition and amplification of the fast flame into detonations. The run-up distance for unstable mixtures was found to be much shorter than anticipated from a model neglecting the fluctuations in a 1-D framework. The run-up distance was also correlated to the detonation cell size, yielding LDDT ̃7 - 50 cells, with the proportionality coefficient depending on X and the obstacle blockage ratio. Finally, a unique correlation for the run-up distance is proposed, yielding LDDT ̃3000 c tr, where c is the sound speed in the shocked non-reacted gas, valid for large X.

Download or read book Guidelines for Postrelease Mitigation Technology in the Chemical Process Industry written by CCPS (Center for Chemical Process Safety) and published by John Wiley & Sons. This book was released on 2010-09-17 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book puts together a body of very recent information never before presented in one volume on the design of post-release mitigation systems. The development of a fundamental knowledge base on post-release mitigation systems, through testing and data correlation, is very new. While further research and development is needed, this practical work offers guidance on putting post-release countermeasures to work now. The book presents current engineering methods for minimizing the consequences of the release of toxic vapors, or ignition of flammable vapors, including passive and active systems intended to reduce or eliminate significant acute effects of a dispersing vapor cloud in the plant facility, or into the surrounding community. As in all CCPS works, the book emphasizes planning and a systems approach, shows limitations of any methods discussed, and provides numerous references so that the reader may continue to learn.

Download or read book WADC Technical Report written by United States. Wright Air Development Division and published by . This book was released on 1959 with total page 1442 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Combustion Flames and Explosions of Gases written by Bernard Lewis and published by Academic Press. This book was released on 2013-10-22 with total page 754 pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion, Flames, and Explosions of Gases, Second Edition focuses on the processes, methodologies, and reactions involved in combustion phenomena. The publication first offers information on theoretical foundations, reaction between hydrogen and oxygen, and reaction between carbon monoxide and oxygen. Discussions focus on the fundamentals of reaction kinetics, elementary and complex reactions in gases, thermal reaction, and combined hydrogen-carbon monoxide-oxygen reaction. The text then elaborates on the reaction between hydrocarbons and oxygen and combustion waves in laminar flow. The manuscript tackles combustion waves in turbulent flow and air entrainment and burning of jets of fuel gases. Topics include effect of turbulence spectrum and turbulent wrinkling on combustion wave propagation; ignition of high-velocity streams by hot solid bodies; burners with primary air entrainment; and description of jet flames. The book then takes a look at detonation waves in gases; emission spectra, ionization, and electric-field effects in flames; and methods of flame photography and pressure recording. The publication is a valuable reference for readers interested in combustion phenomena.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 564 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1989 with total page 1470 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis and Numerics for Conservation Laws written by Gerald Warnecke and published by Springer Science & Business Media. This book was released on 2005-12-05 with total page 541 pages. Available in PDF, EPUB and Kindle. Book excerpt: Whatdoasupernovaexplosioninouterspace,?owaroundanairfoil and knocking in combustion engines have in common? The physical and chemical mechanisms as well as the sizes of these processes are quite di?erent. So are the motivations for studying them scienti?cally. The super- 8 nova is a thermo-nuclear explosion on a scale of 10 cm. Astrophysicists try to understand them in order to get insight into fundamental properties of the universe. In ?ows around airfoils of commercial airliners at the scale of 3 10 cm shock waves occur that in?uence the stability of the wings as well as fuel consumption in ?ight. This requires appropriate design of the shape and structure of airfoils by engineers. Knocking occurs in combustion, a chemical 1 process, and must be avoided since it damages motors. The scale is 10 cm and these processes must be optimized for e?ciency and environmental conside- tions. The common thread is that the underlying ?uid ?ows may at a certain scale of observation be described by basically the same type of hyperbolic s- tems of partial di?erential equations in divergence form, called conservation laws. Astrophysicists, engineers and mathematicians share a common interest in scienti?c progress on theory for these equations and the development of computational methods for solutions of the equations. Due to their wide applicability in modeling of continua, partial di?erential equationsareamajor?eldofresearchinmathematics. Asubstantialportionof mathematical research is related to the analysis and numerical approximation of solutions to such equations. Hyperbolic conservation laws in two or more spacedimensionsstillposeoneofthemainchallengestomodernmathematics.

Download or read book Characterization of Turbulent Flame vortex Dynamics for Bluff Body Stabilized Flames written by Cal Rising and published by . This book was released on 2019 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Modern propulsion systems primarily operate under highly turbulent conditions in order to promote greater efficiency through an increase in mixing. The focus of this thesis is to identify the turbulent flame-vortex interaction to provide insights into the turbulent combustion process. This work is accomplished through the use of turbulent ramjet-style combustor which is stabilized through use of a bluff-body. The facility is equipped with a custom turbulence generator to modulate the incoming turbulence levels to allow flames across various regimes to be analyzed. High-speed particle image velocimetry (PIV) and CH* chemiluminescence diagnostics are implemented to resolve the flow field and flame position. The flame-vortex interaction can be described by the vorticity transport which has four terms; vortex stretching, baroclinic torque, dilatation, and viscous diffusion. The vorticity mechanisms are calculated through the implementation of a Lagrangian tracking scheme, which allows for the individual mechanisms to be decomposed along the path of individual tracks. The mechanisms are compared across different turbulence levels to determine the effects of turbulence on the vorticity mechanisms. The mechanisms are calculated along the flame front as well to determine the individual effects of the vorticity mechanisms on the evolving structure of the turbulent premixed flame. The flame front curvature is also compared across the various turbulence conditions. The results confirm that as the flame-front experiences increased turbulence levels the combustion induced mechanisms of baroclinic torque and dilation decrease, while vortex stretching increases. This is a result of the turbulent energy exchange becoming the controlling factor within the flow-field. In addition, increased flame curvature is experience by the flame front due to increased local baroclinicity and turbulent energy exchange.

Download or read book The Mathematics of Combustion written by John D. Buckmaster and published by SIAM. This book was released on 1985-01-01 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book delves into the rapidly changing area of combustion, in which asymptotic methods and bifurcation theory have made a significant impact as have the constant-density, small-heat-release models and other important contributions.

Download or read book Dynamic Aspects of Detonations written by A. L. Kuhl and published by AIAA. This book was released on 1993 with total page 516 pages. Available in PDF, EPUB and Kindle. Book excerpt: