Download or read book Characteristic Time Correlation for Lean Blowoff of Bluff Body Stabilized Flames written by S. L. Plee and published by . This book was released on 1978 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Development of a Correlation to Predict the Lean Blowout of Bluff Body Stabilized Flames with a Focus on Relevant Timescales and Fuel Characteristics written by Bethany C. Huelskamp and published by . This book was released on 2013 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: In many high-speed reacting flows, a bluff body is used to locally slow the velocity and stabilize the flame. Gas turbine engines, both in ground-based industrial settings, as well as in aviation settings, utilize bluff body stabilized flames, often running at lean fuel-air ratios to extend the equipment's lifetime or to meet emissions regulations. However, running the equipment at a lean condition also puts the system at risk for lean blowout, which can result in facility inefficiencies, hardware damage, and a catastrophic reduction in aircraft performance. This thesis uses experimental data taken at the Air Force Research Laboratory, as well as data collected from a review of past literature, to develop a correlation to predict lean blowout using a least squares curve fit method. The laminar flame speed and ignition delay time were calculated for subsets of the data using the chemical kinetics software Cantera, and the results were incorporated into the correlations. The purpose of this effort was to provide an accurate, practical method of predicting lean blowout for designers and modelers, as well as to provide insight into the critical parameters and timescales that govern the blowout process by examining the significance of each parameter included in the correlation and the physical and chemical processes it may affect. The correlations presented in this thesis indicate that the lean blowout of bluff body stabilized flames is dependent on both the Damkohler number and the Lewis number. U/D is the inverse of the fluid mechanic timescale, likely that of the mixing time in the shear layer between the recirculation zone and the fresh reactants. Pressure, temperature, and the hydrogen to carbon ratio of the fuel all affect the reactivity of the mixture, contributing to the chemical timescale in the Damkohler number. The molecular weight of the fuel influences the mass diffusion, and thereby the Lewis number, of the fuel. As the Lewis number increases, various reaction rates, including the turbulent flame speed, decrease, also affecting the chemical timescale in the Damkohler number. The exact chemical timescale could not be determined from the laminar flame speed and ignition delay time data. A major contribution of this work is establishing the role that fuel characteristics play in the lean blowout process. Very little work has been done in the literature on fuel effects in the lean blowout of bluff body stabilized flames, but the correlation developed clearly shows that both the molecular weight and hydrogen to carbon ratio of the fuel influence the process.

Download or read book Analysis of Blowoff Scaling of Bluff Body Stabilized Flames written by Sajjad A. Husain and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Bluff body stabilization of flames is a commonly employed technique for combustion applications, such as thrust augmentors. These combustors are usually required to operate at lean conditions governed by a lower stability limit on combustion denoted by lean blow off. Lean blow off is believed to be a dynamically unstable phenomenon that leads to flame extinction or convection from a stable, usually desired, point in space. Current theories predict lean blow off based on models that were developed over specific domain of inflow parameters. This thesis sought to compile, re-evaulate, and analyze past blowoff data presented in literature using time scale correlations, Damkohler numbers, by employing modern chemical kinetic solvers to approximate characteristic chemical times. The research has conclusively shown that it is possible to express blowoff data for multiple flow conditions using a power law relationship between Damkohler number and Reynolds numbers. From the analysis of this power law relations, trends are validated using past empirical observations, and some new information regarding flame stability is also conveyed.

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 An Optical Analysis of the Blowoff Behavior for Bluff Body stabilized Flames in Vitiated Flow written by Trevor Ray Jensen and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Optical Analysis of the Blowoff Behavior for Bluff Body stabilized Flames in Vitiated Flow written by Trevor Ray Jensen and published by . This book was released on 2011 with total page 206 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 BLOWOFF CHARACTERISTICS IN INTERACTING PREMIXED V FLAMES written by Joseph Crane and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame interaction is a common phenomenon in many common combustion applications thatcan have a leading order effect on flame stabilization. In particular, flame stabilization is a key performance metric in low-emissions gas turbine engines for both aircraft and power generation applications. In this study, we explore the impact flame interaction on blowoff characteristics and flame shape on three two-dimensional bluff-body stabilized flames by varying the spacing between the bluff bodies and the velocity of the incoming flow. Flame locations are extracted from particle image velocimetry (PIV) data to study the differences in blowoff limits between two different bluff-body spacing configurations all at the same entering bulk flow velocity. Increasing the flame spacing led to wider flamesand less interaction. Geometric and flow profile effects are discussed with respect to flame interaction and blowoff phenomena.

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 0 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:

Download or read book Analysis of Bluff body Flame Stabilization Close to Blow off written by Erdzan Hodzic and published by . This book was released on 2015 with total page 81 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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 Lean Blowoff Characteristics of Swirling H2 co ch4 Flames written by Qingguo Zhang and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes an experimental investigation of lean blowoff for H2/CO/CH4 mixtures in a swirling combustor. This investigation consisted of three thrusts. The first thrust focused on correlations of the lean blowoff limits of H2/CO/CH4 mixtures under different test conditions. It was found that a classical Damköhler number approach with a diffusion correction could correlate blowoff sensitivities to fuel composition over a range of conditions. The second part of this thesis describes the qualitative flame dynamics near blowoff by systematically characterizing the blowoff phenomenology as a function of hydrogen level in the fuel. These near blowoff dynamics are very complex, and are influenced by both fluid mechanics and chemical kinetics; in particular, the role of thermal expansion across the flame and extinction strain rate were suggested to be critical in describing these influences. The third part of this thesis quantitatively analyzed strain characteristics in the vicinity of the attachment point of stable and near blowoff flames. Surprisingly, it was found that in this shear layer stabilized flame, flow deceleration is the key contributor to flame strain, with flow shear playing a relatively negligible role. Near the premixer exit, due to strong flow deceleration, the flame is negatively strained i.e., compressed. Moving downstream, the strain rate increases towards zero and then becomes positive, where flames are stretched. As the flame moves toward blowoff, holes begin to form in the flame sheet, with a progressively higher probability of occurrence as one moves downstream. It is suggested that new holes form with a more uniform probability, but that this behavior reflects the convection of flame holes downstream by the flow. It has been shown in prior studies, and affirmed in this work, that flames approach blowoff by first passing through a transient phase manifested by local extinction events and the appearance of holes on the flame. A key conclusion of this work is that the onset of this boundary occurs at a nearly constant extinction strain rate. As such, it is suggested that Damköhler number scalings do not describe blowoff itself, but rather the occurrence of this first stage of blowoff. Given the correspondence between this first stage and the actual blowoff event, this explains the success of classical Damköhler number scalings in describing blowoff, such as shown in the first thrust of this thesis. The physics process associated with the actual blowoff event is still unclear and remains a key task for future work.

Download or read book Chemistry and Turbulence Effects in Bluff body Stabilized Flames written by J. C. Pan and published by . This book was released on 1992 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 On the Mechanism of Bluff Body Flame Stabilization at Low Velocities written by Tony Maxworthy and published by . This book was released on 1962 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: