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Structure and Propagation of Turbulent Bunsen Flames

Description: From Introduction and Summary: "In the assessments of research objectives after World War II it was brought out that little effort had yet been expended on an understanding of turbulent flames.The present report deals exclusively with a second stage of work which was carried out between November 1954 and August 1959. This summary report includes a few new data, but its chief purpose is to reorient the findings toward a better appreciation of what has been accomplished and what most profitably might be done in the near future."
Date: 1962
Creator: Burgess, David
Partner: UNT Libraries Government Documents Department

An active particle diffusion theory of flame quenching for laminar flames

Description: An equation for quenching distance based on the destruction of chain carriers by the surface is derived. The equation expresses the quenching distance in terms of the diffusion coefficients and partial pressures of the chain carriers and gas phase molecules, the efficiency of the surface as a chain breaker, the total pressure of the mixture, and a constant which depends on the geometry of the quenching surface. Quenching distances measured by flashback for propane-air flames are shown to be consistent with the mechanism. The derived equation is used with the lean inflammability limit and a rate constant calculated from burning velocity data to estimate quenching distances for propane-air (hydrocarbon lean) flames satisfactorily.
Date: March 4, 1952
Creator: Simon, Dorothy M. & Belles, Frank E.
Partner: UNT Libraries Government Documents Department

Studies of OH, CO, CH, and C(Sub 2) Radiation From Laminar and Turbulent Propane-Air and Ethylene-Air Flames

Description: Note presenting an analysis of OH, CO, CH and C(sub 2) radiations from propane-air and ethylene-air flames isolated with a monochromator, and purification of the OH, CH, and C(sub 2) emitters by subtracting the unwanted CO background. The changes in intensity with changing equivalence ratio were determined for each emitter. Results regarding the variation of radiation equivalence ratio in the flame column and variation of emitter intensity with fuel-flow rate and Reynolds number are also provided.
Date: June 1958
Creator: Clark, Thomas P.
Partner: UNT Libraries Government Documents Department

A Hypothetical Burning-Velocity Formula for Very Lean Hydrogen-Air Mixtures

Description: Very lean hydrogen-air mixtures experience strong diffusive-thermal types of cellular instabilities that tend to increase the laminar burning velocity above the value that applies to steady, planar laminar flames that are homogeneous in transverse directions. Flame balls constitute an extreme limit of evolution of cellular flames. To account qualitatively for the ultimate effect of diffusive-thermal instability, a model is proposed in which the flame is a steadily propagating, planar, hexagonal, close-packed array of flame balls, each burning as if it were an isolated, stationary, ideal flame ball in an infinite, quiescent atmosphere. An expression for the laminar burning velocity is derived from this model, which theoretically may provide an upper limit for the experimental burning velocity.
Date: June 30, 2008
Creator: Williams, Forman; Williams, Forman A & Grcar, Joseph F
Partner: UNT Libraries Government Documents Department

Prediction of flame velocities of hydrocarbon flames

Description: The laminar-flame-velocity data previously reported by the Lewis Laboratory are surveyed with respect to the correspondence between experimental flame velocities and values predicted by semitheoretical and empirical methods. The combustible mixture variables covered are hydrocarbon structure (56 hydrocarbons), equivalence ratio of fuel-air mixture, mole fraction of oxygen in the primary oxygen-nitrogen mixture (0.17 to 0.50), and initial mixture temperature (200 degrees to 615 degrees k). The semitheoretical method of prediction considered are based on three approximate theoretical equations for flame velocity: the Semenov equation, the Tanford-Pease equation, and the Manson equation.
Date: January 2, 1953
Creator: Dugger, Gordon L. & Simon, Dorothy M.
Partner: UNT Libraries Government Documents Department

Some effects of small-scale flow disturbance on nozzle-burner flames

Description: Laminar-like and brush-like propane-air flames were obtained when wire grids were used as turbulence generators in a 1/2-inch nozzle burner. The laminar-like flames for grid-disturbed flow had a slightly higher burning velocity than "true" laminar flames (no grid used). The brush-like flames were similar to those obtained with pipe turbulent flow. Their burning-velocity dependence on a "flow disturbance" Reynolds number compared favorably with that obtained for pipe turbulent flames. Hot-wire-anemometer equipment was used to measure the flow disturbance intensity in the cold flow with and without the grids in place.
Date: September 1956
Creator: Wong, Edgar L.
Partner: UNT Libraries Government Documents Department

Formation and Combustion of Smoke in Laminar Flames

Description: "The nature and formation of smoke and its combustion were investigated. Smoke, which consist of tiny mesomorphous crystals tightly packed into popcorn-ball-like particles that agglomerate to give filaments, was found to contain about 5 percent of the hydrogen originally present in the fuel. Factors affecting smoke formation were studied in both diffusion flames and premixed Bunsen flames. It is suggested that smoking tendency increases with increasing stability of the carbon skeleton of the molecule, as determined by relative bond strength" (p. 657).
Date: August 17, 1954
Creator: Schalla, Rose L.; Clark, Thomas P. & McDonald, Glen E.
Partner: UNT Libraries Government Documents Department

Burning Velocities of Various Premixed Turbulent Propane Flames on Open Burners

Description: Note presenting the measurement of turbulent burning velocities for premixed propane flames at room temperature and atmospheric pressure. The measurements were made for systems of various laminar burning velocities, densities, and viscosities. Experimental results and comparison with previous work are provided.
Date: October 1955
Creator: Wagner, Paul
Partner: UNT Libraries Government Documents Department

Experiments on Stability of Bunsen-Burner Flames for Turbulent Flow

Description: "The results of a study of the stability of propane-air flames on bunsen-burner tubes are presented. Fuel-air ratio, tube diameter, and Reynolds number were the primary variables. Regions of stability are outlined in plots of fuel-air ratio as a function of Reynolds number for flames seated on the burner lip and for flames suspended well above the burner" (p. 1).
Date: 1948
Creator: Bollinger, Lowell M. & Williams, David T.
Partner: UNT Libraries Government Documents Department

Flame-visibility tests with individual exhaust stacks

Description: Report presenting testing made on a Wright 1820-G single-cylinder engine to determine the effect of operating variables and the effect of shape and size of the exhaust stack on the visibility of exhaust gases for individual-stack installations. Flame damping was improved by decrease in nozzle-exit area, increase in stack length, and reduction in hydraulic diameter of the exhaust jets. Results regarding the characteristics of exhaust flames and damping of exhaust flames are provided.
Date: February 1944
Creator: Turner, L. Richard & Humble, Leroy V.
Partner: UNT Libraries Government Documents Department

Effect of pressure and duct geometry on bluff-body flame stabilization

Description: Report presenting blowoff velocities and recirculation-zone lengths of propane-air flames stabilized by cylindrical flameholders measured as a function of pressure, cylinder diameter, fuel-air ratio, and tunnel geometry for a range of Reynolds numbers. Results regarding blowoff velocities, recirculation-zone lengths, critical time, and heat losses from recirculation zone are provided.
Date: September 1958
Creator: Potter, Andrew E., Jr. & Wong, Edgar L.
Partner: UNT Libraries Government Documents Department

Further Experiments on the Stability of Laminar and Turbulent Hydrogen-Air Flames at Reduced Pressures

Description: "Stability limits for laminar and turbulent hydrogen-air burner flames were measured as a function of pressure, burner diameter, and composition. On the basis of a simple flame model, turbulent flashback involved a smaller effective penetration distance than laminar flashback. No current theoretical treatment predicts the observed pressure and diameter dependence of laminar and turbulent blowoff" (p. 1).
Date: April 1957
Creator: Fine, Burton
Partner: UNT Libraries Government Documents Department

The Soret Effect in Naturally Propagating, Premixed, Lean, Hydrogen-Air Flames

Description: Comparatively little attention has been given to multicomponent diffusion effects in lean hydrogen-air flames, in spite of the importance of these flames in safety and their potential importance to future energy technologies. Prior direct numerical simulations either have considered only the mixture-averaged transport model, or have been limited to stabilized flames that do not exhibit the thermo-diffusive instability. The so-called full, multicomponent transport model with cross-diffusion is found to predict hotter, significantly faster flames with much faster extinction and division of cellular structures.
Date: June 30, 2008
Creator: Grcar, Joseph F.; Grcar, Joseph F.; Bell, John B. & Day, Marcus S.
Partner: UNT Libraries Government Documents Department

Detailed modeling and laser-induced fluorescence imaging of nitric oxide in a NH(i)-seeded non-premixed methane/air flame

Description: In this paper we study the formation of NO in laminar, nitrogen diluted methane diffusion flames that are seeded with ammonia in the fuel stream. We have performed numerical simulations with detailed chemistry as well as laser-induced fluorescence imaging measurements for a range of ammonia injection rates. For comparison with the experimental data, synthetic LIF images are calculated based on the numerical data accounting for temperature and fluorescence quenching effects. We demonstrate good agreement between measurements and computations. The LIF corrections inferred from the simulation are then used to calculate absolute NO mole fractions from the measured signal.The NO formation in both doped and undoped flames occurs in the flame sheet. In the undoped flame, four different mechanisms including thermal and prompt NO appear to contribute to NO formation. As the NH3 seeding level increases, fuel-NO becomes the dominant mechanism and N2 shifts from being a net reactant to being a net product. Nitric oxide in the undoped flame as well as in the core region of the doped flames are underpredicted by the model; we attribute this mainly to inaccuracies in the NO recycling chemistry on the fuel-rich side of the flame sheet.
Date: December 14, 2001
Creator: Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Bessler, Wolfgang G.; Schulz, Christof; Glarborg, Peter et al.
Partner: UNT Libraries Government Documents Department

Analyzing and Tracking Burning Structures in Lean Premixed Hydrogen Flames

Description: This paper presents topology-based methods to robustly extract, analyze, and track features defined as subsets of isosurfaces. First, we demonstrate how features identified by thresholding isosurfaces can be defined in terms of the Morse complex. Second, we present a specialized hierarchy that encodes the feature segmentation independent of the threshold while still providing a flexible multi-resolution representation. Third, for a given parameter selection we create detailed tracking graphs representing the complete evolution of all features in a combustion simulation over several hundred time steps. Finally, we discuss a user interface that correlates the tracking information with interactive rendering of the segmented isosurfaces enabling an in-depth analysis of the temporal behavior. We demonstrate our approach by analyzing three numerical simulations of lean hydrogen flames subject to different levels of turbulence. Due to their unstable nature, lean flames burn in cells separated by locally extinguished regions. The number, area, and evolution over time of these cells provide important insights into the impact of turbulence on the combustion process. Utilizing the hierarchy we can perform an extensive parameter study without re-processing the data for each set of parameters. The resulting statistics enable scientist to select appropriate parameters and provide insight into the sensitivity of the results wrt. to the choice of parameters. Our method allows for the first time to quantitatively correlate the turbulence of the burning process with the distribution of burning regions, properly segmented and selected. In particular, our analysis shows that counter-intuitively stronger turbulence leads to larger cell structures, which burn more intensely than expected. This behavior suggests that flames could be stabilized under much leaner conditions than previously anticipated.
Date: June 1, 2009
Creator: Bremer, Peer-Timo; Weber, Gunther; Pascucci, Valerio; Day, Marc & Bell, John
Partner: UNT Libraries Government Documents Department

Numerical simulation of low Mach number reacting flows

Description: Using examples from active research areas in combustion andastrophysics, we demonstrate a computationally efficient numericalapproach for simulating multiscale low Mach number reacting flows. Themethod enables simulations that incorporate an unprecedented range oftemporal and spatial scales, while at the same time, allows an extremelyhigh degree of reaction fidelity. Sample applications demonstrate theefficiency of the approach with respect to a traditional time-explicitintegration method, and the utility of the methodology for studying theinteraction of turbulence with terrestrial and astrophysical flamestructures.
Date: June 20, 2007
Creator: Bell, John B.; Aspden, Andrew J.; Day, Marcus S. & Lijewski,Michael J.
Partner: UNT Libraries Government Documents Department

Effect of equivalence ratio on premixed flame response to unsteady strain-rate and curvature

Description: The detailed dynamical response of flames in turbulent reacting flow involves a complex interaction between unsteady flow structures and flame chemistry. Two essential features of this interaction are the unsteady strain-rate and curvature disturbances to the reaction zone. In this work, the authors focus on a single flow length/time scale feature in two dimensions (2D), and its effect on a premixed flame for a range of mixture conditions. In particular, they study the interaction of a premixed freely propagating methane-air flame with a 2D counter-rotating vortex pair in an unbounded domain. In earlier work, they studied this flow using C{sub 1} kinetics, at stoichiometric conditions. Notable observations include the shift of the reaction zone into the products on the vortex-pair centerline, leading to depletion of H, O and OH, and the consequent general drop in reaction rates on the centerline flame segment. Curvature-induced focusing/defocusing effects were observed at the positively curved flame cusp, leading to modifications in internal transport fluxes of various species and radicals in the flame, and associated effects on H production and fuel consumption rates. These results were extended to more detailed kinetics, using other C{sub 1} and C{sub 2} mechanisms, which demonstrated the effect of choice of chemical mechanism on the observed transient flame response. The present study focuses on the dependence of the transient flame response on reactants mixture equivalence ratio. Two reactants mixture conditions are studied: case 1 is a stoichiometric conditions - equivalence ratio {Phi} = 1.0, and case 2 is rich at {Phi} = 1.2. In both cases, the reactants are 20% N{sub 2}-diluted.
Date: November 1, 1997
Creator: Najm, H.N.; Wyckoff, P.S. & Knio, O.M.
Partner: UNT Libraries Government Documents Department

The time evolution of a vortex-flame interaction observed via planar imaging of CH and OH

Description: Planar laser-induced fluorescence imaging diagnostics of OH and CH are used to examine a premixed laminar flame subjected to a strong line-vortex pair. Results are reported for a fuel-rcih lamiar CH{sub 4}-air-N{sub 2} rod-stabilized flame. The flow studied was highly reproducible, which enabled the use of phase-sampled imaging to provide time-resolved image sequences. Image sequences are shown for a condition sufficient to produce localized extinction of the primary flame. Results indicate that a breakage in the CH front is not preceded by any distinct change in the OH front. The structure of the CH and OH profiles during the transient leading up to, and through the breakage of the CH front do not appear to be consistent with the concept of a strained laminar flame.
Date: May 1, 1996
Creator: Nguyen, Quang-Viet & Paul, P.H.
Partner: UNT Libraries Government Documents Department

Combustion Characterization of Coal Fines Recovered from the Handling Plant

Description: Effect of swirl settings on NO{sub x} for three firing rates were investigated. It was found that the variation of NO{sub x} concentrations with respect to the change in swirl numbers was significant. But, the variation of NO{sub x} Concentration with respect to firing rates was found to be consistent with the increase in firing rates. The flame stability was accessed by the visual observation of the flame with relation to the burner quarl.
Date: October 1, 1996
Creator: Masudi, Houshang; Samudrala, Surender Rao; Chenevert, Lisa; Cornelius, Christopher & Dwivedi, S. N.
Partner: UNT Libraries Government Documents Department