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High Lewis Number Premixed Flame Instabilities
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Book Synopsis High-Lewis Number Premixed Flame Instabilities by : Yi Ma
Download or read book High-Lewis Number Premixed Flame Instabilities written by Yi Ma and published by . This book was released on 2009 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Lewis Number Effects on Turbulent Premixed Flame Structure by :
Download or read book Lewis Number Effects on Turbulent Premixed Flame Structure written by and published by . This book was released on 1992 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: The influence of the Lewis number on turbulent flame front geometry is investigated in a premixed turbulent stagnation point flame. A laser tomography technique is used to obtain the flame shape, a fractal analysis of the multiscale flame edges is performed and the distribution of local flame front curvature is determined. Lean H[sub 2]/Air and C[sub 3]H[sub 8]/Air mixtures with similar burning rates were investigated with Lewis numbers of 0.33 and 1.85 respectively. At the conditions studied the laminar H[sub 2]/Air mixture is unstable and a cellular structure is observed. Turbulence in the reactant is generated by a perforated plate and the turbulent length scale (3mm) and intensity (7%) at the nozzle exit are fixed. The equivalence ratio is set so that the burning velocity is the same for all the cases. Results show clearly that the turbulent flame surface area is dependent on the Lewis number. For a Lewis number less than unity surface area production is observed. The shape of the flame front curvature distribution is not found to be very sensitive to the Lewis number. For the H[sub 2]/Air mixture the distribution is skewed toward the positive values indicating the presence of cusps while for the C[sub 3]H[sub 8]/Air mixture the distribution is more symmetrical. In both cases the average curvature is found to be zero, and if the local burning speed varies linearly with curvature, the local positive and negative burning velocity variations due to curvature will balance.
Book Synopsis Experimental Studies of the Effect of Gravity on the Stability of Premixed Laminar Flames by : Corey Martin Dunsky
Download or read book Experimental Studies of the Effect of Gravity on the Stability of Premixed Laminar Flames written by Corey Martin Dunsky and published by . This book was released on 1991 with total page 642 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Hydrogen Flare Stack Diffusion Flames by :
Download or read book Hydrogen Flare Stack Diffusion Flames written by and published by . This book was released on 1970 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Chambered Diffusion Flame for General Lewis Numbers by : Yung-Sze Choi
Download or read book Chambered Diffusion Flame for General Lewis Numbers written by Yung-Sze Choi and published by . This book was released on 1986 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Instabilities of a Rich Premixed-flame by : Jonathan Robert Vincent
Download or read book Instabilities of a Rich Premixed-flame written by Jonathan Robert Vincent and published by . This book was released on 2000 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Experimental and Numerical Study of the Inwardly-propagating Premixed Flame by : Alfonso F. Ibarreta
Download or read book An Experimental and Numerical Study of the Inwardly-propagating Premixed Flame written by Alfonso F. Ibarreta and published by . This book was released on 2002 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dynamics and Stability of Premixed Flames by : V. V. Bychkov
Download or read book Dynamics and Stability of Premixed Flames written by V. V. Bychkov and published by . This book was released on 2000 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Structure and Stability of Near-limit Flames with Low Lewis Number by : Kenneth N. Whaling
Download or read book Structure and Stability of Near-limit Flames with Low Lewis Number written by Kenneth N. Whaling and published by . This book was released on 1991 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Two-dimensional Stability of Laminar Flames by : H. S. Mukunda
Download or read book Two-dimensional Stability of Laminar Flames written by H. S. Mukunda and published by . This book was released on 1992 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Non-premixed Jet Flame Instabilities by : Marc Füri
Download or read book Non-premixed Jet Flame Instabilities written by Marc Füri and published by . This book was released on 2001 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Effects of Differential Diffusion in Counter-flow Premixed Flames with Dilution and Enrichment by : Ehsan Abbasi Atibeh
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." --
Book Synopsis Studies in Premixed Combustion. [Benjamin Levich Inst. for Physico-Chemical Hydrodynamics, City College of CUNY, New York, New York]. by :
Download or read book Studies in Premixed Combustion. [Benjamin Levich Inst. for Physico-Chemical Hydrodynamics, City College of CUNY, New York, New York]. written by and published by . This book was released on 1993 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the period under review, significant progress was been made in studying the intrinsic dynamics of premixed flames and the problems of flame-flow interaction. (1) A weakly nonlinear model for Bunsen burner stabilized flames was proposed and employed for the simulation of three-dimensional polyhedral flames -- one of the most graphic manifestations of thermal-diffusive instability in premixed combustion. (2) A high-precision large-scale numerical simulation of Bunsen burner tip structure was conducted. The results obtained supported the earlier conjecture that the tip opening observed in low Lewis number systems is a purely optical effect not involving either flame extinction or leakage of unburned fuel. (3) A one-dimensional model describing a reaction wave moving through a unidirectional periodic flow field is proposed and studied numerically. For long-wavelength fields the system exhibits a peculiar non-uniqueness of possible propagation regimes. The transition from one regime to another occurs in a manner of hysteresis.
Book Synopsis Fundamentals of Premixed Turbulent Combustion by : Andrei Lipatnikov
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
Book Synopsis Turbulent Premixed Flames by : Nedunchezhian Swaminathan
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.
Book Synopsis Diffusive-thermal Instability of Counter-flow Flames Ot Low Lewis Number by : Carsten Kaiser
Download or read book Diffusive-thermal Instability of Counter-flow Flames Ot Low Lewis Number written by Carsten Kaiser and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Physical and Chemical Processes in Flames by :
Download or read book Physical and Chemical Processes in Flames written by and published by . This book was released on 2007 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the present program was to study the structure and response of laminar premixed and nonpremixed flames with emphases on effects of high pressure, flame/flow unsteadiness, and chemistry. Studies on flame dynamics show strong coupling between the intrinsic flamefront hydrodynamic cellular instabilities and the diffusional/thermal cellular or pulsating instabilities, for mixture Lewis numbers that are respectively smaller or larger than unity. Linear and nonlinear stability analyses on diffusion flames show regimes of stability and the influence of heat loss on their boundaries. Studies on combustion chemistry led to the determination of laminar flame speeds of high fidelity at atmospheric and high pressures for CO/H2 as well as C2-C3 mixtures with air, and the counterflow ignition temperatures of dimethyl ether (DME) and 1,3-butadiene, allowing developments of detailed and reduced reaction mechanisms. A mathematical theory and computational algorithm termed directed relation graph was developed and then further improved that allows systematic and rapid determination and thereby elimination of unimportant species and reactions of detailed mechanisms, leading to skeletal mechanisms that are sufficiently small either for computational simulation of complex combustion phenomena. These results are expected to be useful to the general interests of AFOSR in the fundamental and practical issues of flame dynamics and chemical kinetics, turbulent combustion, soot formation, radiative heat transfer, flame extinction, stabilization, flammability, and supersonic combustion.