Characterization of Fast Flames for Turbulence-induced Deflagration to Detonation Transition PDF Download
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Author: Jessica Marcella Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 27
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Book Description
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.
Author: Jessica Marcella Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 27
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Book Description
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.
Author: Jessica Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 76
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Book Description
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.
Author: Hardeo Chin
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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Book Description
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.
Author: Rachel Hytovick
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author: Jonathan Sosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 117
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Book Description
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.
Author: Jonathan Sosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
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.
Author: United States. Wright Air Development Division
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1442
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Book Description
Author: M.Y. Hussaini
Publisher: Springer Science & Business Media
ISBN: 1461228840
Category : Science
Languages : en
Pages : 668
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Book Description
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.
Author: Mohamed Saifelislam Abdelgadir Ahmed
Publisher:
ISBN:
Category : University of Ottawa theses
Languages : en
Pages :
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Book Description
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.
Author: CCPS (Center for Chemical Process Safety)
Publisher: John Wiley & Sons
ISBN: 0470935081
Category : Technology & Engineering
Languages : en
Pages : 194
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Book Description
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.
