Download or read book Effect of Differential Diffusion on Flame Stabilization in a Syngas Jet in Turbulent Cross flow written by and published by . This book was released on 2015 with total page 2 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Fuel Composition and Differential Diffusion on Flame Stabilization in Reacting Syngas Jets in Turbulent Cross flow written by and published by . This book was released on 2015 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H2 in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization are located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays an important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H2 or CO species reveals that hydrogen contributes significantly to premixing, particularly in explosive zones in the upstream leeward region, i.e. at the preferred flame stabilization location. Therefore, a small amount of H2 diffuses much faster than CO, creating relatively homogeneous mixture pockets depending on the competition with turbulent mixing. These pockets, together with high H2 reactivity, contribute to stabilizing the flame at a consistent location regardless of the CO concentration in the fuel for the present range of DNS conditions.

Download or read book Advanced Turbulent Combustion Physics and Applications written by N. Swaminathan and published by Cambridge University Press. This book was released on 2022-01-06 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explore a thorough overview of the current knowledge, developments and outstanding challenges in turbulent combustion and application.

Download or read book And Effect of Differen al Diffusion on Flame Stabiliza on in a Syngas Jet in Turbulent Cross flow written by and published by . This book was released on 2015 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Sustainability in Biofuel Production Technology written by Pratibha S. Agrawal and published by John Wiley & Sons. This book was released on 2022-08-26 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sustainability in Biofuel Production Technology Explore current challenges and the latest technologies in biofuel production In Sustainability in Biofuel Production Technology, a team of engineers and chemists delivers a thorough and accessible exploration of the source of renewable energy biofuels poised to help conserve natural resources and limit the impact of fossil fuel use. The book offers detailed information about the challenges and trends in biodiesel production and includes contributions from leading researchers in the field of biodiesel production. Readers will explore aviation biofuels, biofuel production technologies, reactor design and safety considerations, and the modelling and simulation of biofuel production as they move through the book’s 14 chapters. The authors also analyze the performance of biofuels along with cost estimations and mathematical modeling of various process parameters. Readers will also find: A thorough introduction to biofuels, including their history, generation, classification, and relevant technologies In-depth presentations of the production technologies of biofuels, including chemical and biological production processes Comprehensive explorations of the utilization of biofuels in aviation, including performance analyses and safety considerations Fulsome discussions of key issues and challenges in biofuels production pathways and the environmental effects of biofuels Perfect for academic researchers and industrial scientists working in the biofuels, bioenergy, catalysis, and materials science sectors, Sustainability in Biofuel Production Technology will also be suitable for members of regulatory bodies in the bioenergy sector.

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 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 An Experimental Investigation of Jet Diffusion Flames written by Ho-Nam Bang and published by . This book was released on 1996 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Simulation of Flame Stabilization of Lifted Turbulent Jet Diffusion Flames written by Ming Chen and published by . This book was released on 2000 with total page 179 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.

Download or read book The Effect of Turbulent Diffusion on Flame Stabilization written by Probhatendu Prosad Roy Choudhury and published by . This book was released on 1958 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental and Theoretical Study of the Turbulent Diffusion Flame in Cross flow written by P. E. Botros and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Pilot Flame Stabilization on Gas Jet Flames in a Cross flow written by S. R. Gollahalli and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of Finite Rate Chemistry Effects on Turbulent Jet Diffusion Flames and Non homogeneous Autoigntion Using the One Dimensional Turbulence Model written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In current study Numerical simulation of turbulent combustion process is approached using One Dimensional Turbulence (ODT) model. The ODT model is based on the coupling of molecular processes (reaction and diffusion) with turbulent transport in a spatially- and temporally-resolved fashion over a one-dimensional domain. The domain corresponds to a transverse (or radial) direction; while, the transient evolution of the thermo-chemical scalars on the 1D domain represents the spatial evolution downstream of the jet inlet. The linear-eddy approach for modeling molecular mixing in turbulent flow involves stochastic simulation on a 1D domain with sufficient resolution to predict all relevant physical length scales properly. Firstly ODT is carried out to predict the hydrogen and air jet diffusion flame with helium dilution in the fuel. The comparison with existing experimental data was made for the numerical result of ODT simulation of jet diffusion flames in both conditional means and rms of scalars of measurements and computational results. Another application of ODT was made in present work to verify the capability of prediction of autoignition (self-ignition) of one of free shear layer flow -- jet diffusion flow. Different range of pressure and Reynolds number are set to identify the effects of turbulence intensity and mixture properties on the self-ignition chemistry. Autoignition delay time was studied based on these different conditions. At the same time the ability of the prediction of mixture temperature and species mass fraction profile were tested. A principle numerical result is expected and discussed. Conditional pdf and progress variable were used to analyze the computational result of ODT. Analysis was focus on the temperature growth and the mass fraction distribution of intermediate species and product.

Download or read book Differential Diffusion in a Turbulent Jet written by Thomas Michael Lavertu and published by . This book was released on 2006 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Also presented are the first experimental measurements of the spectrum of the normalized concentration difference, EZ(K1 eta). These revealed the scales at which differential diffusion manifests itself. In all instances, these spectra were observed to decrease with wavenumber over all wavenumbers, consistent with a flow dominated by the decay of its scalar field. Although differential diffusion effects are molecular in origin, they persist at scales larger than the Kolmogorov scale." --

Download or read book On Diffusion Flames in Turbulent Shear Flows Modeling Reactant Consumption in a Planar Fuel Jet written by W. B. Bush and published by . This book was released on 1977 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: The turbulent portion of the planar fuel jet, for isobaric subsonic flow, under fast direct one-step irreversible reaction between unpremixed fuel and oxidant, is analyzed. Mean spatial profiles for the dependent variables are found numerically and analytically from the governing nonlinear partial differential equations, based on an explicit eddy diffusion, and on a mean rate of reactant consumption proportional to the product of the mean mass fraction of fuel, the mean mass fraction of oxidant, and the appropriate local characterization of the mean rate of strain. Results from the model are qualitatively, and, in many cases, quantitatively, compatible with experimental data. (Author).

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