Showing papers on "Diffusion flame published in 1980"
TL;DR: The sooting behavior of laminar diffusion flames were altered by addition of diluents to the fuel flow as discussed by the authors, and the effect of water vapor, carbon dioxide and sulphur dioxide in reducing the tendency to soot was purely thermal with no observable chemical interaction.
Abstract: The sooting behavior of laminar diffusion flames were altered by addition of diluents to the fuel flow. Fuel additives which decrease the sooting tendency had an effectiveness in order of their molar specific heat capacity; helium exhibited some exaggerated trends, probably due to its high thermal diffusivity. The effect of water vapor, carbon dioxide and sulphur dioxide in reducing the tendency to soot was purely thermal with no observable chemical interaction. Trace amounts of oxidizers and halogenated compounds increased the sooting tendency substantially. Results from tests with blended fuels and fuel-hydrogen nitrogen mixtures in which the C/H ratio and temperature were controlled revealed that C/H ratio was not a dominant parameter in the sooting tendency. These results and temperature measurements provided evidence that the sooting behavior of a diffusion flame is controlled by the initial fuel pyrolysis which is dominated by the flame temperature and the field it causes. Since accurate ca...
265 citations
TL;DR: In this article, the authors used the Burke and Schumann flame sheet concept to locate the stoichiometric fuel-oxygen interface and, hence, the points of heat release in a laminar methane-air diffusion flame.
251 citations
TL;DR: For downwardly propagating flames in pyrex tubes at atmospheric pressure and intial temperature of 295°K, measurements were made of the nitrogen dilution required for quenching as a function of the hydrogen-oxygen ratio, as well as of flame temperatures, flame speeds, temperature gradients behind the flame, unburnt hydrogen, and cell sizes as mentioned in this paper.
142 citations
TL;DR: In this article, a concentric diffusion flame arrangement, sooting heights were determined as a function of the oxygen concentration in the oxidizing stream, and it was shown that increasing the oxygen concentrations also increases the particle burn-up rate in the vicinity of the flame.
Abstract: In a concentric diffusion flame arrangement, sooting heights were determined as a function of the oxygen concentration in the oxidizing stream. Changing the oxygen concentration has two different and competing effects on the tendency of a fuel jet to soot. Increasing the oxygen concentration increases the stoichiometric flame temperature which in turn increases the fuel pyrolysis and soot formation rates. However, increasing the oxygen concentration also increases the particle burn-up rate in the vicinity of the flame. The initial effect dominates at high oxygen concentrations and the latter at low concentrations. In most practical combustor systems, the temperature would appear to be the controlling parameter.
85 citations
01 Feb 1980
69 citations
TL;DR: In this paper, a method of selenium hydride atomization using a cool highly fuel rich-hydrogen-oxygen diffusion flame burning in the inlet part of a T-shaped quartz tube placed in the optical axis of an atomic absorption spectrometer is investigated.
68 citations
TL;DR: In this article, local soot concentrations in polystyrene and polypropylene flames were measured in order to shed light on the position and thus the mechanisms of carbon-particle formation in diffusion flames.
67 citations
TL;DR: In this paper, the stability of a uniformly curved propagating flame front is investigated and it is shown that the uniform front becomes unstable if the Lewis number L of the limiting reaction component is less than some critical number $L_c $, and if the radius of the front is greater than a critical value $R_c$.
Abstract: Experiments with laminar flames in gaseous combustible mixtures show that for certain mixtures a flame front will often break up into numerous cells. Cellular flames are periodic structures with pointed crests, pointing in the direction of the burned gas. The smoother sections (troughs) of the front are convex toward the fresh mixture. The flame appears darker at its crests than at its troughs, which indicates that the temperature at the crests is lower than in other parts of the cell. Sometimes the flame in the vicinity of the crests disappears entirely. We employ a model derived by Matkowsky and Sivashinsky to consider the stability of a uniformly curved propagating flame front. We show that the uniform front becomes unstable if the Lewis number L of the limiting reaction component is less than some critical number $L_c $, and if the radius of the front is greater than a critical value $R_c $. When the critical values are exceeded, perturbations of the uniform front evolve to a cellular front which bifu...
49 citations
TL;DR: In this article, an unsteady spherically symmetric formulation of the droplet heat conduction problem with no internal motion and with a time-varying heat flux specified at the surface as a boundary condition is presented.
47 citations
01 Jan 1980
TL;DR: In this article, the authors used an approximation solution to develop relationships for flame lengths, angles, heights, and tip velocities for fires heading with the wind and burning in calm air as functions of Byram's fire intensity, I (Btu/ft-sec).
Abstract: -Equations describing flow in buoyant turbulent jets have been applied to the derivation of characteristics for forest fire flames. Approximate solutions are used to develop relationships for flame lengths, angles, heights, and tip velocities for fires heading with the wind and burning in calm air as functions of Byram's fire intensity, I (Btu/ft-sec). Flame length and velocity relationships are tested with data taken during controlled burns in southern fuels and with data from the literature. Backfire data are described by the equations for calm-air conditions. Both theoretical and experimental results show that flame lengths for backfires and headfires vary as I~ and I l!z. respectively; flame tip velocities vary as I v., and I \12 .
TL;DR: In this article, the temperature and composition profiles obtained by probing a confined, axisymmetric-laminar methane-air diffusion flame suggest that a state of partial equilibrium exists in the high-temperature primary reaction zone.
TL;DR: In this paper, an experimental study was performed on the magnitude of different mechanisms by which heat is transferred from the flaming region to the unburnt fuel ahead of the flame for flames propagating horizontally over the surface of a solid fuel.
Abstract: An experimental study is performed on the magnitude of the different mechanisms by which heat is transferred from the flaming region to the unburnt fuel ahead of the flame for flames propagating horizontally over the surface of a solid fuel. Measurements of the gas velocity field, temperature fields and radiant flux distribution in a particular case of laboratory scale flame spread over a thick fuel are used to determine the magnitude of the heat fluxes ahead of the flame. The results show that, for this particular case, although heat conduction through the solid is dominant, radiation from the flame contributes significantly to the heat transfer process. An analysis of the development of the fire indicates that there is a transition in the mechanisms of heat transfer as the fire grows. While in the early stages of the fire, heat conduction through the solid is dominant, radiation from the flame becomes of increased importance as the size of the fire increases.
TL;DR: In this paper, temperature measurements were made in a turbulent free-jet diffusion flame, that include average and fluctuating values as well as probability spectral densities, and statistical quantities of mean value, variance, skewness, and flatness of the temperature distribution were determined from the measured probability density function.
TL;DR: In this article, three effects found during the measurement of oxides of nitrogen produced by liquid fuel diffusion flames are reported, and the cause of high NO leadings indicated by the chemiluminescent analyzer fo...
Abstract: Three effects found during the measurement of oxides of nitrogen produced by liquid fuel diffusion flames are reported. In each experiment a diffusion flame at one atmosphere pressure was formed around a horizontal fuel wetted cylinder. In the first experiment a porous metal cylinder of 5.2 mm diameter was wetted by normal heptane and placed in a low velocity stream of ambient air. Soot escaping from the turbulent wake of the diffusion flame was deposited on the surfaces of a large collection system located above the flame. This collection system drew in all of the flame products plus some entrained ambient air. The soot was found to give off NO slowly at ambient temperature and more rapidly when healed. The NO from the soot amounted to 20 percent of the gas phase NO produced by the flame. In the second experiment, a quartz microprobe was used to take gas samples along a horizontal line perpendicular to the cylinder axis. The cause of high NO leadings indicated by the chemiluminescent analyzer fo...
Patent•
10 Oct 1980
TL;DR: A fuel gas burner produces a short fan-shaped flame and has primary utility in oil-to-gas furnace conversions as discussed by the authors, where the burner includes swirl generating blades disposed in an annulus between a burner barrel carrying the bulk of the combustion gas and a mixing tube carrying approximately a 1.1 air/gas mixture.
Abstract: A fuel gas burner produces a short fan-shaped flame and has primary utility in oil-to-gas furnace conversions. The burner includes swirl generating blades disposed in an annulus between a burner barrel carrying the bulk of the combustion gas and a mixing tube carrying approximately a 1.1 air/gas mixture. The blades induce a violent, turbulent action to the combustion gas to encourage formation of the short flame. The flame is preferably formed with a fan shape.
01 Jan 1980
TL;DR: In this paper, a single component laser Doppler anemometry system is used to investigate the centerline locations of the fuel and air stagnation points for different rates of combustion.
Abstract: The ducted, bluff-body research combustor can be viewed as dual coaxial jets consisting of an annular air jet and a central fuel jet. Due to the cylindrical geometry of the bluff body, the recirculation zone is in the form of a toroidal vortex wherein a reverse flow occurs along the centerline towards the bluff body. The reverse flow is in direct opposition to the flow of the central fuel jet. This situation is analogous to the flowfield established by two opposing jets. A fuel stagnation point occurs inside the vortex and an air stagnation point occurs at the end of the vortex when the strength of the reverse flow jet is greater than that of the fuel jet. A single component laser Doppler anemometry system is used to investigate the centerline locations of the fuel and air stagnation points for different fuel and air flow rates. The results of cold flow experiments are presented where the fluid in the fuel jet is either air or carbon dioxide. Gaseous propane fuel is used in the combusting experiments. The differences between the combusting and cold flow results are discussed. Also, a possible connection between the location of the fuel stagnation point andmore » the overall combustion inefficiency of the flame is examined.« less
TL;DR: In this article, a four-equation turbulence model consisting of the turbulent kinetic energy, the dissipation rate and the density-velocity correlations using unweighted statistics is suggested.
TL;DR: In this article, the effects of low Btu gas composition and combustor design on NO/sub x/ emissions were examined on three atmospheric pressure flame reactors: diffusion flame reactor, flat flame reactor and catalytic reactor.
Abstract: Effects of low Btu gas (LBG) composition and combustor design are examined on NO/sub x/ emissions. Low Btu gases of varying compositions were synthesized from bottled gases and fired in three atmospheric pressure flame reactors: diffusion flame reactor, flat flame reactor and catalytic reactor. Nitrogen oxide emissions were found to be most sensitive to the concentrations of NH/sub 3/ and hydrocarbon fuel gas in the synthetic LBG. Lowest NO/sub x/ emissions were produced by the diffusion flame reactor operating at near stoichiometric conditions and the catalytic reactor operating fuel rich. Paper No. 79-GT-185.
TL;DR: In this paper, an acoustically tuned flame tube was used to measure fundamental flame speed and flammability envelopes of premixed propane/air and methane/air that contain minute amounts of CF3Br.
TL;DR: In this paper, the second-law performance of several combustion processes has been analyzed in terms of the exergy subsidy which they require, and the reference potentials have been tabulated in terms with the ambient partial pressures of CO2, H2O, and O2.
TL;DR: In this paper, Nitric oxide and hydrogen cyanide concentration distributions in an unseeded, laminar, atmospheric methane-air diffusion flame were analyzed in order to gain insight into the role nitrogen-containing species play in influencing NO formation in such flames.
Abstract: Nitric oxide and hydrogen cyanide concentration distributions established in an unseeded, laminar, atmospheric methane-air diffusion flame have been analyzed in order to gain insight into the role nitrogen-containing species play in influencing NO formation in such flames. The experimental data indicate that HCN and NO formation are strongly dependent on the local stoichiometry within the flame region. Cyanide formation occurs only within the fuel-rich luminous flame core, presumably via reaction between hydrocarbon radicals and molecular nitrogen or nitric oxide. The cyanide species are subsequently partially converted to nitric oxide on the fuel-lean side of the primary reaction zone, contributing 15-30 percent of the total nitric oxide production by the flame. The nitric oxide concentration profiles peak on the fuel-lean side of the flame in the zone where the thermal production of NO by the extended Zeldovich mechanism occurs.
TL;DR: In this paper, a turbulent diffusion flame burner is shown to demonstrate that the summation of fixed-nitrogen species (NO + HCN + NHi) is a significant measure of a flame's emission potential.
TL;DR: In this article, a streamwise laminar diffusion flame in a boundary layer flow is modelled for a hydrogen-oxygen system with six step reaction kinetics, based on the existence of a large value of the Damkohler number, providing first order inner and outer temperature and concentration solutions from which composite series are constructed for a range of fresstream reactant concentrations.
Abstract: A streamwise laminar diffusion flame in a boundary layer flow is modelled for a hydrogen-oxygen system with six step reaction kinetics. The method of matched asymptotic expansions, based on the existence of a large value of the Damkohler number, provides first order inner and outer temperature and concentration solutions from which composite series are constructed for a range of fresstream reactant concentrations, some of which are chosen to coincide with experimental situations. In these cases comparisons between theoretical and experimental results are made
01 Jan 1980
TL;DR: In this article, a two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step, and the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps were investigated.
Abstract: A two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step. Studied were: (1) the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps; (2) the effect of inlet temperature and reference velocity on combustion efficiency; (3) CO, NO2 and NO sub x production in the flame; and (4) the blowout and upstream propagation of the flame. In the ranges studied, the large coherent structures dominated both the reacting and the nonreacting free shear layers behind the step. The growth of the vortices and the propagation of the flamer were intimately linked. Vortex pairing was observed to be one of the mechanisms for introduction of fresh reactants into the shear layer and growth of the shear layer. Probe composition measurements of the flame showed that, in the recirculation zone, the reaction was above 99 percent complete, CO and unburnt hydrocarbons were above the equilibrium level NO sub x concentration was far below the equilibrium level and NO2 comprised a negligible fraction of NO sub x.
TL;DR: In this article, the S-response of a diffusion flame in a chamber is considered, in particular the top bend corresponding to ignition, and the upper branch is found to be stable and the middle branch unstable, the neutral point lying exactly at the bend.
TL;DR: In this paper, the two-dimensional, laminar, mixed-mode convection, boundary-layer radiative diffusion flame has been analytically investigated with emphasis on the nongray nature of the combustion products.
Abstract: The two-dimensional, laminar, mixed-mode convection, boundary-layer radiative diffusion flame has been analytically investigated with emphasis on the nongray nature of the combustion products. The solution procedures include Shvab-Zeldovich approximation and von Mises transformation for the physical transport equations and the finite difference method for the computation of the transformed equations. The local radiative fluxes for nongray, gray and radiatively-ideal gases are prescribed. Twelve parameters that govern the flame characteristics have been identified. In addition to extensive results of distributions in the field variables and fluxes, the ratio of the radiation loss to the combustion energy evolved was computed and a radiatively-ideal gas having behaviors similar to the nongray gases was identified.
TL;DR: In this paper, the radiative properties of gas combustion products are obtained using a spectral method especially well adapted for small scale tests and the initial temperature and species profiles needed are given by the resolution of the conservation equations without radiation.
Abstract: The main purpose of this work is to calculate the radiative properties and the radiative fluxes at each location through a fully developed turbulent boundary layer over a solid reacting surface with a diffusion flame. The radiative properties of gas combustion products are obtained using a spectral method especially well adapted for small scale tests. The initial temperature and species profiles needed are given by the resolution of the conservation equations without radiation. The computed emissivities for various gas mixtures including or not soot are in agreement with previous results. The computational method has been used for different systems: polyethylene or polystyrene with O2 or air. The results confirm that the contribution of radiation heat transfer to burning rate is negligible compared to convective heat transfer in a laboratory scale test. Radiative heat transfer tends to increase combustion rate only for high soot volume fraction. The values obtained for the various fluxes are in g...