Showing papers on "Diffusion flame published in 1968"
TL;DR: In this article, a study of the noise produced by turbulent premixed flames stabilized on open burners is described, and it is shown that such flames may be represented acoustically as a collection of monopole sound sources in the combustion zone.
Abstract: A study of the noise produced by turbulent premixed flames stabilized on open burners is described. It is shown that such flames may be represented acoustically as a collection of monopole sound sources in the combustion zone. The radiated sound pressure is dependent on the rate of change of the rate of increase of volume of the gas during combustion, which varies owing to the turbulence in the flow. The rate of volume increase is proportional to the rate of consumption of combustible gas mixture in the flame. To measure this quantity, an optical technique has been developed which relies on observations of changes in the intensity of emission from the free radicals C 2 or CH generated in the reaction zone. Good quantitative agreement is obtained between the radiated sound pressures calculated from these intensity measurements and the values recorded simultaneously with a microphone. A correlation observed between the mean emission intensities of C 2 and CH radicals and the total flow rate of combustible gas mixture both in the laminar and turbulent flames, and in their transition region, supports the wrinkled laminar flame concept of turbulent flame propagation.
261 citations
10 Jun 1968
TL;DR: A review of previous studies of the burning behavior and flame structure of composite ammonium perchlorate (AP) propellants can be found in this paper, where the granular diffusion flame (GDF) theory conforms to the known structure of the propellant flame and is quantitatively valid for a wide class of practical AP propellants, much more so than any other theory proposed for composite propellants.
Abstract: : Theories of propellant burning are briefly reviewed in the light of previous studies of the burning behavior and flame structure of composite ammonium perchlorate (AP) propellant. Those studies showed that the granular diffusion flame (GDF) theory conforms to the known structure of the propellant flame, and is quantitatively valid for a wide class of practical AP propellants, much more so than any other theory proposed for composite propellants.
76 citations
TL;DR: In this paper, the effect of diluent flow on soot production in laminar ethylene diffusion flames has been studied by measurement of smoke points and of the rates at which soot leaves a smoking flame.
63 citations
TL;DR: In this article, the stability of hydrogen-air diffusion flames has been studied at ambient temperature and pressure, with hydrogen injector diameter and lip thickness as primary geometric variables, and regions of stable flame were found for large variations in hydrogen and air flow.
46 citations
TL;DR: In this article, the effects of increasing additions of oxygen to the fuel have been investigated and the amounts of chloroform-soluble material, polycyclic aromatic hydrocarbons (PCAH), and carbonaceous residue in the dry soot recovered from ethylene-air and ethane-air diffusion flames respectively have been determined.
45 citations
TL;DR: In this article, the authors studied the effects of the wall temperature and the jet temperature on the extinction speed of a wall of combustible material and the opposed jet diffusion flame in the wall jet case.
43 citations
TL;DR: In this article, the effects of changes in the oxygen index (i.e., the mole fraction of oxygen in the mixture) of oxygen-nitrogen and oxygen-argon mixtures supplied to the flame have been investigated.
43 citations
TL;DR: This paper describes the separation of the air-acetylene and nitrous oxide- acetylene flames, and some applications of these flames in analytical flame spectroscopy.
Abstract: Premixed hydrocarbon-air flames invariably show two separate reaction zones. In the primary zone, the combustible gas mixture burns principally to carbon monoxide, hydrogen, and water, and in the outer mantle, or secondary diffusion flame, the hot gases burn with atmospheric oxygen to carbon dioxide and water. Teclu [J. Prakt. Chem. 44, 246 (1891)] and Smithells and Ingle [Trans. Chem. Soc. 61, 204 (1892)] independently demonstrated the existence of these two zones in various premixed hydrocarbon-air flames, using the flame separator. This device consists of a wide glass or silica tube fitted over the bunsen type burner to form an extension above the inner burner port. The primary combustion then occurs at the inner burner port, while the pale blue secondary diffusion flame is maintained at the top of the outer glass tube. An alternative method of separation of premixed hydrocarbon-air flames consists of sheathing the flame with an inert gas to lift off or separate the secondary diffusonzone. The interconal zone of flames separated by these methods are extended in length and exhibit very low radiative background. The interconal zone also contains the hottest part of the flame, and can be viewed without interference from radiation produced in a secondary diffusion zone that would normally surround it in separated flames. It is the hot interconal zone of premixed flames that is most frequently employed in analytical flame photometry, because it is in this region that the greatest population of atoms occurs when elements are introduced into the flame by nebulization of solutions of their salts. Thus, separated flames may be employed with advantage in thermal emission, atomic absorption, and atomic fluorescence spectroscopy. This paper describes the separation of the air-acetylene and nitrous oxide-acetylene flames, and some applications of these flames in analytical flame spectroscopy.
34 citations
TL;DR: A long path-length diffusion flame is also particularly useful in atomic-absorption measurements because it absorbs very little radiation in the far ultraviolet region and gives an abundance of arsenic atoms.
32 citations
TL;DR: In this article, the resonance-line emission from the SnH species in a nitrogen-hydrogen diffusion flame is used to determine the presence of ground-state tin atoms in the diffusion flame.
Abstract: Tin can be determined in the range 3 to 3000 p.p.m. by molecular-band emission from the SnH species in a nitrogen-hydrogen diffusion flame. The emission at 609·5 nm, which is almost line-like, gives a limit of detection of 1·5 p.p.m. of tin. Spectral interference from sodium is eliminated by use of a didymium filter. The presence of oxygen gives rise to a much broader spectrum, caused by tin(II) oxide formation, with a visual limit of detection of 5 p.p.m. of tin. Atomic emission can be observed only in the presence of alcohols, e.g., isopropyl alcohol, but a high concentration of ground-state tin atoms exists in the diffusion flame. Mechanisms are discussed to explain the production of tin atoms, SnH and the resonance-line emission.
28 citations
TL;DR: In this article, self-absorbed radiation from solid carbon particles in an axially symmetric propane diffusion flame, as well as from the sodium D line (5890 A), was examined spectroscopically.
Abstract: Self-absorbed radiation from solid carbon particles in an axially symmetric propane diffusion flame, as well as from the sodium D line (5890 A), was examined spectroscopically. Radial distributions of the emission and absorption coefficients were obtained by inverting lateral specific intensity data. The temperature distribution was obtained by applying Kirchoff's law to the local emission and absorption coefficients. Carbon particle temperature agrees with the sodium D line temperature over a major portion of the carbon zone. Absorption measurements of the carbon particles were made at wavelengths ranging from 2330 A to 11,000 A. From these measurements, the size of the carbon particles is estimated to be between 200 A and 300 A.
TL;DR: In this article, a simplified scheme of four chemical reactions is chosen to represent the kinetics of the hydrogen-oxygen system; m particular, this scheme includes the influence of the hydroxyl radical.
Abstract: A simplified scheme of four chemical reactions is chosen to represent the kinetics of the hydrogen-oxygen system; m particular, this scheme includes the influence of the hydroxyl radical. The diffusion flame supported by this set of reactions is assumed to form behind a (planar, two-dimensional) body of parabolic meridian profile with downstream-pointing vertex. The body initially separates the oxygen and hydrogen streams, which are assumed to have equal speeds and pressures far upstream. (The pressure is subsequently assumed to be constant everywhere.) For pressures of about one atmosphere it is found that nett reaction rates can be treated as infinitely fast, the four reactions then yield four chemical equilibrium equations whose behaviour is dominated by the largeness of the equilibrium constant for the (thermal) dissociation-recombination reaction of hydrogen. The flame-sheet model emerges as the limiting solution when the reciprocal of this large quantity is allowed to vanish. The method of matched asymptotic expansions is used to investigate the structure of the flame which results from a relaxation of this limit. The results bear a satisfactory resemblance to some experimental measurements which, although made in other gas mixtures, exemplify the behaviour of the type of diffusion flames considered.
TL;DR: In this article, the critical fuel-oxygen ratio for soot formation and its dependence on temperature and pressure are discussed for various hydrocarbons, and the effects of electric fields and foreign additives have been given consideration.
Abstract: The critical fuel-oxygen ratio for soot formation and its dependence on temperature and pressure are discussed for various hydrocarbons. It is shown in the case of the Bunsen flame that the shape and structure of the flame front also have a decisive effect on soot formation. In the reaction zone of fuel-rich hydrocarbon flames, unsaturated compounds are formed, and the concentration profiles of these products can provide quantitative information about their importance in soot formation. The “mechanism” of soot formation is discussed on the basis of the concentrations of higher hydrocarbons and the variation of the number and size of the soot particles. The effects of electric fields and foreign additives on soot formation have been given consideration.
TL;DR: In this article, a study of the response of a diffusion flame sheet to perturbations of reactant concentration which are introduced, either as changes in the free streams, or as appropriate initial distributions throughout the field.
Abstract: A study is made of the response of a diffusion flame sheet to perturbations of reactant concentration which are introduced, either as changes in the free streams, or as appropriate initial distributions throughout the field. Species’ and energy conservation requirements are approximated by linearized boundary-layer equations; general solutions are derived for species, enthalpy and temperature distributions, as well as for the flame sheet shape, and a number of specific problems are solved.
TL;DR: The construction and performance of a highly efficient total consumption burner that produces a nonturbulent acetylene-nitrous oxide flame from premixed gases that is convenient to operate and can be quickly assembled from commercially available components is reported on.
Abstract: It is well known that most of the burners presently used to produce high temperature, premixed flames have the tendency to be discouragingly wasteful of the sample solution, often bringing only a small fraction of the amount used into the flame. This paper reports on the construction and performance of a highly efficient total consumption burner that produces a nonturbulent acetylene–nitrous oxide flame from premixed gases. The eighteen flame emission detection limits tabulated for a select group of elements compare favorably with the best values heretofore reported in the literature, and the apparent freedom of alkaline earth emission from phosphate interference indicates the total consumption flame here described to be less subject to chemical interference than is the conventional diffusion flame. The relatively low cost burner that has been developed is convenient to operate and can be quickly assembled from commercially available components.
01 Jan 1968
TL;DR: In this paper, a special form of Damkohler's first number was examined for the stabilization of hydrogen diffusion flames by flame-holders in supersonic flow of low stagnation temperatures.
Abstract: Experiments on the stabilization of hydrogen diffusion flames by flame-holders in supersonic flow of low stagnation temperatures are reported. The examination of a special form of Damkohler's first number shows that the maximum blow-off velocity at the burning limit of a flame strongly increases with the laminar flame velocity of the fuel-air mixture. According to this, hydrogen is very well suited for the stabilization of flames by flame-holders in supersonic flow. This is confirmed by experiments which show that the burning limit of a flame is not influenced by the velocity of sound. Starting from this, tests have been carried out on the burning limits of flame-holder-stabilized flames, where the fuel is injected into the air from the flame-holder base. The burning limits have been measured for different flame-holder diameters and different injection angles up to a Mach number of 2.1. The burning limits can be considerably extended when the injection angle is increased from 0° to 90°. Furthermore, the influence of different conditions for the mixing of air and fuel have been investigated. Variations of the base pressure under the action of the flame have been measured.
TL;DR: In this paper, the effect of adding oxygen to a very fuel-rich perchloric acid flame has been examined and the second flame is shown to be a methane-oxygen flame.
01 Jun 1968
TL;DR: Flame propagation in supersonic premixed flows of hydrogen and air ignited by coaxial, hot gas was studied in this paper, where a pilot jet was equipped with a fire extinguisher.
Abstract: Flame propagation in supersonic premixed flows of hydrogen and air ignited by coaxial, hot gas, pilot jet
TL;DR: In this article, the authors described the combustion inhibition effect of a potassium salt on propane-air flames by the change of the activation energy of the overall chemical reaction, i.e., the decrease of the chemical reaction rate, was shown both analytically and experimentally.
Abstract: This study describes the combustion inhibition effect of a potassium salt on propane-air flames by the change of the activation energy of the overall chemical reaction. The extinction limit of an opposed jet diffusion flame and the laminar burning velocity of a premixed burner flame of propane-air were measured to obtain the activation energies. From a theoretical analysis of the opposed jet diffusion flame, the overall activation energy of the chemical reaction against the seeded quantities of potassium salt was calculated using the extinction limit data. Through increasing the potassium salt percentages, the increase of the activation energy, i.e. the decrease of the chemical reaction rate, was shown both analytically and experimentally. The ratio of the activation energies with potassium salt to the ones without obtained from the burning velocity of the premixed flame closely agreed with that from the opposed jet diffusion flame. The relation between the seeded quantities of potassium salt and the activation energies of the overall chemical reaction of propane-air was quantitatively obtained.
TL;DR: In this paper, the authors dealt with the oscillatory combustion occurring in the diffusion flame of liquid fuel spray burning and found that major part of the fuel burns as the droplet flames.
Abstract: This paper deals with the oscillatory combustion occurring in the diffusion flame of liquid fuel spray burning. Main results obtained are as follows. (1) Major part of the fuel burns as the droplet flames. Most of these droplets burn penetrating the surrounding gas and with the flame type of a wake flame. (2) Fluctuation of burning rate that is the driving force of oscillation is brought about by the transition phenomenon of the flame type of droplets. From the above result, the magnitude of the pressure fluctuation can be correlated with the burning condition by using a parameter f. (3) Dependency of the frequency on the combustor length agrees well with the prediction obtained in 1st Report and the dependency of that on the burning condition can be explained quantitatively by examining the relation between the burning condition and the parameters |B| and ∈ which are the synthetic parameters representing the burning condition.
TL;DR: In this paper, the effect of the swirling motion on the flame and its flow field for different values of the Schmidt number was studied, and solutions of the full Navier-Stokes equation and the mass transfer equation were obtained.
Abstract: A steady laminar diffusion flame burning in the core of a vortex is studied. Solutions of the full Navier‐Stokes equation and the mass‐transfer equation are obtained to study the effect of the swirling motion on the flame and its flow field for different values of the Schmidt number. The flow conditions depend on two parameters: Γ∞, the circulation of the vortex and Re, the Reynolds number based on the velocity at the axis of symmetry. The velocity distribution is strongly affected by the circulation. As Γ∞ increases when Re remains constant the width of the jet flow in the core region also increases. However, the mass concentration distribution and the position of the flame depend principally on Re, and on Γ∞ only slightly.
TL;DR: In this paper, the authors studied the mechanism of the oscillatory combustion by applying the equation of continuity, equation of motion and equation of energy to the unsteady flow in combustor and found that the driving force of oscillation is the fluctuation of heat adding rate.
Abstract: In this paper, the mechanism of the oscillatory combustion is studied by applying the equation of continuity, the equation of motion and the equation of energy to the unsteady flow in combustor. Main results obtained are as follows. (1) The driving force of oscillation is the fluctuation of heat adding rate, so the magnitude of both pressure and velocity fluctuations is proportional to the fluctuation of heat adding rate. (2) The frequency of oscillation has a similar dependency on the combustor length with an acoustic resonance frequency. But, since the phase shift of the velocity fluctuation at x=x2 occurs through the interaction between the combustion field and the acoustic field, the frequency is always shifted, more or less, from such resonance frequency and the amount of such frequency shift depends on the flame type and the burning condition. (3) The amplifying conditions of oscillation are made clear and are classified by the distribution diagram of the pressure amplitude.
TL;DR: In this article, an experimental investigation of the aerodynamic properties of a premixed laminar flame system is reported, which is of the Hoelscher-Biedler design and produces a lifted axisymmetric flat flame.
TL;DR: In this paper, an investigation was conducted in order to determine the flame-spreading characteristics of an opposed-jet stabilized flame and their relation to chamber combustion efficiency in a standard combustion tunnel at atmospheric pressure.
Abstract: An investigation was undertaken in order to determine the flame-spreading characteristics of an opposed-jet stabilized flame and their relation to chamber combustion efficiency. Tests were conducted in a standard combustion tunnel at atmospheric pressure, using premixed propane and air as reactants. The approach velocities in the test section were subsonic, ranging from 65 to 140 fps. The equivalence ratio of the mainstream ranged from 0.8 to 1.47. A chamber combustion efficiency equation based on the increase in the rate of momentum was used to study the variation of chamber combustion efficiency in the flame spreading region. This efficiency was shown to correlate with the fraction of the duct cross-sectional area occupied by the flame, as well as the fraction of the inlet mass flow rate which was burning. The entrainment characteristics of the opposed-jet stabilized flame were examined downstream from the tip of the opposed-jet tube. The increase of the burning mass with respect to the burning area was found to be dependent on the percentage of the duct area that was occupied by the flame. The theory of Miesse, which relates combustion efficiency and flame shape, was shown to correlate with the experimental data for certain values of the order of reaction and Damkohler's first ratio.
TL;DR: In this article, a technique was described in which sound waves were produced by modulating the flow rate of oxygen to a small diffusion flame, and the modulating signal could be reproduced acoustically simply by amplifying the photometric recording of direct flame luminosity.
Abstract: A COMMUNICATION1 has drawn attention to the possibility of using flames as sound recorders and amplifiers. A technique was described (Fig. 1 of ref. 1) in which sound waves were produced by modulating the flow rate of oxygen to a small diffusion flame. The region of sound generation, it was stated, is associated with that of maximum flame luminosity, and this luminosity contains the imposed modulation. The authors suggested that the modulating signal could be reproduced acoustically simply by amplifying the photometric recording of direct flame luminosity.