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Showing papers on "Diffusion flame published in 1971"


Journal ArticleDOI
TL;DR: In this paper, the formation of soot particles is regarded as a result of a branched-chain process and of the destruction of active particles on the surface of the soot particle being formed.

240 citations


Journal ArticleDOI
01 Jan 1971
TL;DR: In this paper, an experimental study was made of the structure of the laminar counterflow diffusion flame established in the forward stagnation region of a porous cylinder, and the reaction-rate profiles of stable species and the heat-release-rate profile throughout the flame zone were analyzed.
Abstract: An experimental study was made of the structure of the laminar counterflow diffusion flame established in the forward stagnation region of a porous cylinder. Aerodynamic, temperature, and stable-species-concentration profiles were measured in detail for methane flames at atmospheric pressure. These distributions were analyzed to yield the reaction-rate profiles of stable species and the heat-release-rate profile throughout the flame zone. Results show that, although the maximum concentrations of various intermediate products are observed between the luminous reaction zone and the stagnation point, various chemical reactions, including generation and consumption of such intermediate products, occur in the comparatively narrow region in and around the luminous reaction zone. The maximum rates of consumption of carbon monoxide and generation of carbon dioxide are found on the air side of the flame, and reaction-rate profiles of various stable species are qualitatively similar to those for the two-stage reaction in premixed hydrocarbon-air flames. The comparatively large convection velocity across the flame zone plays an important role, yielding the unique concentration profiles throughout the flame zone. The heat-release-rate profile shows a small valley (negative value) on the fuel side of the major peak, which is attributed to pyrolysis-type reactions. Two kinds of blowoff mechanisms of the present counterflow diffusion flame—namely, thermal quenching of the flame and chemical limitations on the combustion rate—can be clearly explained.

129 citations


Journal ArticleDOI
TL;DR: In this paper, a semiquantitative mechanism was proposed for the alkaline earth metals; its basis is that these metals undergo a homogeneous, gas-phase reaction with flame gases to produce hydroxyl radicals which rapidly remove soot or soot precursors.

109 citations


Journal ArticleDOI
TL;DR: In this paper, a modified Richardson number is proposed as a criterion for laminar-turbulent transition stability in free boundary layers, and experiments were carried out in three systems.

82 citations


Journal ArticleDOI
TL;DR: In this article, the formation of oxides of nitrogen in the burned gas region of premixed oxy-propane flames burning at atmospheric pressure was investigated using an argon-shielded laminar flame.
Abstract: Experimental results are presented for the formation of oxides of nitrogen in the burned gas region of premixed oxy-propane flames burning at atmospheric pressure. The majority of the experiments were conducted using argon-shielded laminar flames, and a lean and a rich flame were studied each containing two different amounts of nitrogen. Data are also presented for a rich oxy-propane flame burning unshielded on a commercial glass blowing torch. The use of mathematical modelling of the rate of nitric oxide in the laminar flames has been investigated. It has been shown that reasonable agreement between experimental and computed profiles can be obtained simply by the use of the two reactions. coupled with K1=107.93cm3 mole-1 sec-1 at 2880 K.

50 citations


Journal ArticleDOI
01 Jan 1971
TL;DR: Gravitational effects on laminar gas jet diffusion flame stability, including zero gravity environment, were studied in this article, where the effects of gravity on diffusion flame were investigated.
Abstract: Gravitational effects on laminar gas jet diffusion flame stability, including zero gravity environment

31 citations


Journal ArticleDOI
TL;DR: In this article, the structure of flat diffusion flames on a Parker-Wolf hard burner is compared with theoretical predictions of perturbation solutions which incorporate realistic schemes for the chemical kinetics, and it is suggested that the consequent disruption of mixing in, or shielding of, the reaction zone makes extinction a progressive process.
Abstract: Results of an experimental investigation of the structure of flat diffusion flames on a Parker-Wolf hard burner are compared with theoretical predictions of perturbation solutions which incorporate realistic schemes for the chemical kinetics. Measurements of hydroxyl radical concentrations show that the flames are reaction-broadened for temperatures below I950°K, while at higher temperatures reaction zone structure is of equilibrium-broadened type. Experiment also shows that, close to extinction, there is significant convective transfer of material from one stream to the other at the flame base. It is suggested that the consequent disruption of mixing in, or shielding of, the reaction zone makes extinction a progressive process. Complementary studies of spherical and counter flow diffusion flames suggest that the former geometry is preferable in future studies designed to test hypotheses about the role of kinetics in diffusion flame extinction.

30 citations


Journal ArticleDOI
Ulrich Bonne1
TL;DR: In this paper, Radiative heat transfer effects on small fires in zero gravity spacecraft and free falling chamber environments from diffusion flame models are investigated. But the authors focus on the effects of radiative heat on small fire in zero-gravity spacecraft and space station environments.

27 citations


Journal ArticleDOI
TL;DR: In this article, the authors extended Essenhigh and Csaba's model for plane flame propagation through a coal dust cloud to incorporate heat generation due to chemical reaction, and they used the nonlinear differential energy equation to evaluate burning velocity, temperature profile, and the heat generation rate along the flame axis.

25 citations


01 Jun 1971
TL;DR: In this paper, a planar diffusion flame is established between an axi-symmetric,'stagnation-point' flow of gaseous oxidant and the pyrolysis product vapors emerging from the polymer surface lying below.
Abstract: : A means for producing combustion of polymers under well-controlled conditions has been employed for study of their fundamental combustion characteristics. In the subject work, a planar diffusion flame is established between an axi-symmetric, 'stagnation-point' flow of gaseous oxidant and the pyrolysis product vapors emerging from the polymer surface lying below. Surface regression rate, surface temperature, and oxidant mass flow rate (the principal control variable) were determined. Plexiglas, Plexiglas-55, polyethylene, polypropylene, Delrin, nylon 6-6, ICRPG polyurethane binder, and polystyrene were tested. Surface regression rate and surface temperature were correlated by means of an Arrhenius function, and these results are utilized to examine previously proposed models of the surface pyrolysis process. The surface regression rate and oxidant mass flow rate were used with a fluid-dynamic analysis of the combustion region to predict the effective heat of gasification for each of the above mentioned polymers. Applications and implications of the above findings are discussed. (Author)

20 citations


Journal ArticleDOI
TL;DR: In this article, an experimental investigation of the flame structure of metal vapor-phase diffusion flames, in particular the low-pressure flames of Mg, Ca, and Sr, is described.
Abstract: This paper describes an experimental investigation of the flame structure of metal vapor-phase diffusion flames, in particular the low-pressure flames of Mg, Ca, and Sr. Two types of experiments were employed. In the first type, metal wire samples were mounted between electrodes and heated electrically. In the second type, a two-dimensional diffusion flame burner was adapted to low-pressure metal combustion studies. Space-resolved spectroscopy was used to define the location of emitters in both experiments. A new model for the flame structure is presented. The model is characterized by a broad reaction zone in the inner region of the luminous envelope. The radiation is attributed mainly to a thermal excitation mechanism. As a result of the reaction (which is thought to be predominantly homogeneous), a large supersaturation of oxide vapor is generated in the inner zone leading to rapid nucleation of particles. Various possible kinetic steps for the reaction are compared. It is concluded that the t...

Journal ArticleDOI
01 Feb 1971-Talanta
TL;DR: A capillary burner supporting a nitrogen/hydrogen diffusion flame has been evaluated as a possible means of detection for several volatile fluorides after their gas-chromatographic separation.

Journal ArticleDOI
TL;DR: In this article, the combustion characteristics of premixed laminar graphite-oxygen-nitrogen flames have been studied at atmospheric pressure both with and without added hydrocarbon, and the variation of particle burning time with initial oxygen partial pressure and oxygen/fuel ratio has been described by first-order combustion kinetics with due consideration for oxygen depletion during burnout.
Abstract: A convenient apparatus for dispersing uniform clouds of solid particles for laboratory dust flame experiments has been tested. The combustion characteristics of premixed laminar graphite-oxygen-nitrogen flames have been studied at atmospheric pressure both with and without added hydrocarbon. The variation of particle burning time with initial oxygen partial pressure and oxygen/ fuel ratio has been described by first-order combustion kinetics with due consideration for oxygen depletion during burn-out. Flame velocity measurements indicate very slow propagation compared with hydrocarbon sprays and aluminum clouds of similar particle diameter. Added chlorine did not measurably affect graphite combustion up to concentrations of 2.5 vol. % in the presence of added hydrocarbon, but less than 1.0 vol. % of chlorine extinguished pure graphite-oxygen flames. The addition of 1.5 to 4.75 wt.% of lead acetate visibly stabilized the graphite-oxygen flame, but the effect on the flame velocity and burning rate ...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the characteristics of flames propagating in vertical tubes in the direction of steep methane-air concentration gradients of about 1.3 volume-percent methane per cm using interferometric techniques.
Abstract: Characteristics of flames propagating in vertical tubes in the direction of steep methane-air concentration gradients of about 1.3 volume-percent methane per cm were investigated using interferometric techniques. The maximum flame velocity for upward and downward propagation in both 2.5- and 5.0-cm diameter tubes occurred in the fuel-rich region; lower flame speeds were observed with the smaller tube diameter at corresponding methane concentrations. Following flame extinguishment in upward propagation, the hot product gas region behind the flame front continued to rise in a predictable fashion as a coherent column into the nonflammable fuel-rich region. This hot column rose at a constant velocity, approximately equal to the flame speed at the time of flame extinguishment. Flame extinguishment limits in the layered mixtures were found not to be strongly dependent on tube diameter. Interferometric techniques developed in this study appear to be useful for the rapid measurements of flammability limi...

Journal ArticleDOI
TL;DR: In this article, the conservation equations of chemical species' conservation equations are shown to involve two small parameters and to give rise to singular perturbation problems, and a criterion for the retention in a solution of both parameters is established.
Abstract: Solutions of the chemical species' conservation equations are shown to involve two small parameters and to give rise to singular perturbation problems. General results are derived for arbitrary flame geometry and a criterion for the retention in a solution of both parameters is established.

Journal ArticleDOI
TL;DR: In this paper, a premixed metal vapor-oxygen system for studying these kinetics was approximated by the combination of a shock tube with an exploding Mg wire particle generator.
Abstract: Homogeneous kinetics may play a large role in dictating diffusion flame structure for metals like Mg. A premixed metal vapor-oxygen system for studying these kinetics was approximated by the combination of a shock tube with an exploding Mg wire particle generator. This portion of the study was unsuccessful because the experimental data indicate the dispersion to consist of MgO rather than Mg particles. A kinetic mechanism is postulated which is consistent with the spectrometric observations. Certain wave interactions in the shock tube which severely curtail experimental times behind the reflected shock are also discussed.

Journal ArticleDOI
TL;DR: In this paper, a new optical setup for increasing the intensity of atomic fluorescence flame spectrometry is presented, which consists of two concave spherical mirrors and an elliposidal mirror whose primary focus is located at the flame position, and secondary at the entrance slit of the monochromator.
Abstract: A new optical setup for increasing the intensity of atomic fluorescence flame spectrometry is presented. The arrangement consists of two concave spherical mirrors and an elliposidal mirror whose primary focus is located at the flame position, and secondary at the entrance slit of the monochromator. Approximately 10 times gain in the measured intensities was obtained. The system is also useful for flame emission work, for which about five times gain was observed. With a low background flame such as the air–H2 for the N2–H2 diffusion flame and 400 μ slits, calcium can be detected at the level of 0.005 μg/ml. Moreover, the observed thermally assisted anti-Stokes fluorescence of In and Ga can be of analytical importance since the detection limits with a total consumption burner and the air–H2 flame were found to be 0.015 and 0.02 μg/ml, respectively. Detection limits in atomic fluorescence for Cr, Tl, In, and Fe are also presented.

Journal ArticleDOI
TL;DR: In this paper, a method is presented for predicting a confined, turbulent, axisymmetrical duct flow in which a diffusion flame occurs, and a model is developed for its prediction which is incorporated into an existing solution procedure for the convective and diffusive transfers of momentum, heat and matter.
Abstract: A method is presented for predicting a confined, turbulent, axisymmetrical duct flow in which a diffusion flame occurs. Radiation is important and a model is developed for its prediction which is incorporated into an existing solution procedure for the convective and diffusive transfers of momentum, heat and matter.

Journal ArticleDOI
01 Jan 1971-Analyst
TL;DR: In this paper, the total phosphate content of detergent materials is determined by measurement of the HPO molecular species at wavelength 528 nm in a cool hydrogen-nitrogen diffusion flame.
Abstract: The total phosphate content of detergent materials is determined by measurement of the emission of the HPO molecular species at wavelength 528 nm in a cool hydrogen-nitrogen diffusion flame. Preliminary treatment with cation-exchange resin is necessary to remove interference by metals. Analytical results on detergent samples containing up to 20 per cent. of phosphates (expressed as P2O5) indicate a precision of the order of 2 to 4 per cent. for the method.

Journal ArticleDOI
TL;DR: In this paper, an analysis of the ionization current drawn from a flame ionization detector having cylindrical symmetry is made, where an idealized representation of the flame is used which enables a relation to be defined between the applied voltage and the current drawn by the flame, and the expression contains factors dependent on geometry and concentration.
Abstract: An analysis is made of the ionization current drawn from a flame ionization detector having cylindrical symmetry. An idealized representation of the flame is used which enables a relation to be defined between the applied voltage and the current drawn from the flame, and the expression contains factors dependent on geometry and concentration. Results of experiments confirm the basic form of this expression for both positive and negative currents drawn from a premixed hydrogen + nitrogen + oxygen flame. The expression also holds for positive currents drawn from the hydrogen + nitrogen diffusion flame, but cannot yet satisfactorily account for negative currents at high rates of flow of hydrogen.

Journal ArticleDOI
01 Jan 1971
TL;DR: In this article, an equation for the rate of combustion in laminar flames is proposed and experiments were made with a turbulent flame in a horizontal water-cooled furnace with an i.i.d. of 0.47 m.
Abstract: The rate of combustion of soot in turbulent flames can differ significantly from that in laminar flames. This paper reports on a study of the rate of combustion in turbulent flames, beginning with a review of the rate of combustion of soot in laminar flames. It is shown that no boundary layer can exist between the soot particle surface and the gas close to the surface. Nevertheless, the specific surface reaction rate of soot can be shown to be 0.01 that of carbon. An equation for the rate of combustion in laminar flames is proposed. Experiments were made with a turbulent flame in a horizontal water-cooled furnace with an i.d. of 0.47 m. Samples drawn from different parts of the flame indicate no significant difference in the mean soot-particle diameter (200 ). It is shown that the axial decay of the amount of soot in a turbulent flame cannot be predicted simply by application of a laminar rate equation and local time-mean values of temperature, oxygen pressure, and soot concentration. The reason for this seems to be that the time-mean values of the oxygen pressure fail, due to the inhomogeneity caused by turbulence, to represent the oxygen pressure close to the soot-particle surface. On the other hand, it is shown that, when the calculated gradients of the flow rate of soot are based on the minimum time-mean value of the oxygen pressure of a cross section, there is agreement with the observed gradients.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the velocities associated with ionic winds when the entrainment to the system is confined to the ion source (i.e., the flame in combustion systems), account being taken of the effect of gauze electrodes on both pressure drop and breakdown strength.

Journal ArticleDOI
01 Jan 1971
TL;DR: In this article, a method for determining the area A of premixed flames is presented, based on measuring the saturation current J 3. (J 3 / A ), the saturation-current density, is the total rate of ion generation per unit area of front, a constant for each initial composition and state of the mixture.
Abstract: A new method for determining the area A of premixed flames is presented, based on measuring the saturation current J 3 . ( J 3 / A ), the saturation-current density, is the total rate of ion generation per unit area of front—a constant for each initial composition and state of the mixture. The limitations of the method due to space charge are discussed. Measurements are then carried out on steady, fluctuating, turbulent, and expanding flame fronts. It is confirmed for laminar flames of various shapes that, for each particular mixture, the saturation current is basically proportional to volumetric flow rate, except as modified by entrainment. Transition from laminar to turbulent flow destroys this linearity suddenly and discontinuously. This differs from the behavior of flames which oscillate as a whole, and is discussed in terms of the “wrinkled-flame-front” hypothesis of turbulent burning. The method is found to have adequate time resolution to record transient fluctuations in turbulent flames. The principle is also applied to expanding flame surfaces following ignition, and is shown to provide a new method of measuring burning velocity in this form.

Patent
26 Oct 1971
TL;DR: A procedure for the production of ACETYLENE-ETHYLENE MIXTURES by mixing at least one light-striped HYDROCARBON with OXYGEN or an OXYgen CONTAINing GAS to form a first mixture is described in this paper.
Abstract: A PROCESS FOR THE PRODUCTION OF ACETYLENE-ETHYLENE MIXTURES BY MIXING AT LEAST ONE LIGHT SATURATED HYDROCARBON WITH OXYGEN OR AN OXYGEN CONTAINING GAS TO FORM A FIRST MIXTURE, AND REACTING THE FIRST MIXTURE IN A FLAME REACTION WHEREIN THE IMPROVEMENT COMPRISES REACTING THE HYDROCARBON WITH THE OXYGEN OR OXYGEN CONTAINING GAS IN A DIFFUSION FLAME TO FORM A SECOND MIXTURE CONTAINING ACETYLENE AND ETHYLENE. A DEVICE FOR CARRYING OUT THE PROCESS IS PROVIDED.

01 Jul 1971
TL;DR: In this article, the combustion characteristics of premixed laminar graphite-oxygen-nitrogen flames, both with and without added hydrocarbon, have been studied at atmospheric pressure.
Abstract: : A convenient apparatus for dispersing uniform clouds of solid particles for laboratory dust-flame experiments has been tested. The combustion characteristics of premixed laminar graphite-oxygen-nitrogen flames, both with and without added hydrocarbon, have been studied at atmospheric pressure. The variation of particle burning time with initial oxygen partial pressure and oxygen/fuel ratio has been described by first-order combustion kinetics, with due consideration for oxygen depletion during burnout. Flame velocity measurements indicate very slow propagation of the above mixes when compared with that of hydrocarbon sprays and aluminum clouds of similar particle diameter and concentration. Added chlorine did not measurably affect graphite combustion up to concentrations of 2.5 vol. % in the presence of added hydrocarbon, but mixes of less than 0.8 vol. % of chlorine extinguished pure graphite-oxygen flames. The addition of 1.5 to 4.75 wt. % of lead acetate visibly stabilized the graphite-oxygen flame, but the effect on the flame velocity and burning rate could not be measured. Stable suspensions of 60 wt. % carbon black in various hydrocarbons have been prepared. The initial phases of the chemical and physical properties evaluation of these are reported. (Author)

Journal ArticleDOI
TL;DR: In this paper, the authors studied the phenomenon of chemiluminescent emission from atoms introduced into hydrocarbon flames and proposed a single excitation mechanism with available energy in excess of 8.5 eV.
Abstract: The phenomenon of chemiluminescent emission from atoms introduced into hydrocarbon flames has been studied in a basic hydrogen-oxygen diffusion flame at low hydrocarbon concentrations. Emissions from several atoms are first order in methane concentration and examination of the relative populations of the excited states of arsenic suggests a single excitation mechanism with available energy in excess of 8.5 eV. Previously proposed mechanisms are discussed and the available evidence favors the processas the origin of the energy of excitation.

Journal ArticleDOI
TL;DR: In this paper, the jet flames of rich propane-air mixtures in a counter air stream were examined by means of visual observation and temperature and concentration measurements, and a concept of similar flame based on the temperature profile at the maximum temperature section was introduced.
Abstract: This paper deals with the jet flames of rich propane-air mixtures in a counter air stream. At a constant jet nozzle pressure a stable combustion can be obtained within the appropriate ranges of the air-fuel ratio of the jets and the velocity of the counter air streams. In order to examine the fundamental characteristics of the flames, the behaviour of some typical flames within the stability curve is studied by means of visual observation and temperature and concentration measurements. A concept of similar flame based on the temperature profile at the maximum temperature section is introduced and confirmed experimentally. By using this concept a dimensionless flame stability curve can be obtained. The temperature, concentration and heat release rate profiles give a good explanation of the estimated relationship between the flame and flow pattern.

Journal ArticleDOI
TL;DR: In this paper, the authors considered turbulent motion of premixed chemically active gases in an infinite system of plane turbulent jets in the presence of diffusive combustion and proposed a method for determining the distribution of all the parameters in the mixing zone, including the longitudinal pressure.
Abstract: We consider turbulent motion of premixed chemically active gases in an infinite system of plane turbulent jets in the presence of diffusive combustion. The proposed calculation method permits determining the distribution of all the parameters in the mixing zone, including the longitudinal pressure. Numerical examples of the calculation of hydrogen combustion in air are presented.

15 Dec 1971
TL;DR: In this article, the kinetics of high-temperature reactions associated with solid-propellant deflagration are studied quantitatively by means of the heterogeneous opposed flow diffusion flame, where a cylindrical gas jet containing the gaseous fuel impinges on the surface of a solid propellant composed of ammonium perchlorate (AP) and copper chromite (CC) catalyst.
Abstract: : The kinetics of high-temperature reactions associated with solid- propellant deflagration are studied quantitatively by means of the heterogeneous opposed flow diffusion flame. In these experiments a cylindrical gas jet containing the gaseous fuel impinges on the surface of a solid propellant composed of ammonium perchlorate (AP) and copper chromite (CC) catalyst. A diffusion flame is established in the stagnation region formed by the two opposed flows of reactants. With increasing mass flux of gaseous fuel, the mass flux of solid AP/CC grows until a limiting condition is reached governed by the kinetics of reaction. Further enhancement in fuel flow does not result in any increase in the mass consumption rate of solid oxidizer.

15 Dec 1971
TL;DR: In this paper, a theoretical analysis of the heterogeneous opposed flow diffusion flame (HOFD) is presented, where a gaseous reactant impinges on a solid reaction undergoing sublimation (or vaporization) and a diffusion flame is established at the stagnation point.
Abstract: : A theoretical analysis is presented of the heterogeneous opposed flow diffusion flame (HOFD). In such a system a gaseous reactant (G) impinges on a solid reaction (S) undergoing sublimation (or vaporization) and a diffusion flame is established at the stagnation point. With increasing mass flux of the gaseous reactant (mG) the mass flux of solid reactant (mS) grows until the total consumption rate of reactants reaches a limiting value due to limitations imposed by the kinetics of reaction. The analysis of the axi-symmetrical stagnation point flow with chemical reaction allows evaluation of the kinetics of chemical reaction at temperatures of interest to combustion processes. (Author)