Showing papers on "Diffusion flame published in 1974"

Mixing Processes in a Free Turbulent Diffusion Flame

Abstract: An experimental study has been made of a pure gaseous turbulent diffusion flame issuing from a circular orifice into stagnant room temperature air surroundings. Measurements have been made in the flame and corresponding nonburning jet, of temperature, velocity, specie concentration and turbulence intensity by the gas tracer diffusion method. The potential core region in the flame is longer than in the cold jet and the rate of spread of the flame is slower than in the corresponding cold jet. Empirical equations are given for the decay along the axis of velocity and concentration as well as for the radial profiles. Diffusion coefficients in the flame are lower than those in the cold jet near the nozzle and this situation is reversed in the far flow region. Turbulence intensities are lower in the flame than in the cold jet. The diffusion coefficient in a flame is not constant. Turbulence intensities determined by the gas tracer diffusion method compares favourably with alternative methods of measuri...

Potassium iodide chemiluminescence in diffusion flames and the KI upper-state potential

Abstract: Chemiluminescence spectra of potassium iodide have been measured in a dilute diffusion flame apparatus. A total of 54 fluctuation bands have been resolved. An analysis of these results as well as previous potassium iodide spectra is presented. By using molecular beam scattering data an extremely accurate excited state potential for potassium iodide is obtained.

Concentration Fluctuations in Turbulent Jet Diffusion Flames

Abstract: A model for the concentration fluctuations in a turbulent diffusion flame is presented. It incorporates the features of intermittency, random fluctuations of stoichiometry within the turbulent fluid and of fuel and oxygen separation either side of the reaction front. It is used to give time mean composition in the flow as well as composition as isokinetically sampled. The use of the model in theoretical calculations and the interpretation of experimental data is explained. Concentration fluctuations derived in this way from measurements in a hydrogen jet diffusion flame in a co-flowing stream of air are also presented.

The Spectra of Organic Flames

Abstract: A preliminary description of the principal features of the spectra of Bunsen-type flames has been given in Chapter I. Here the various band systems encountered in flames will be described in detail and the evidence from which the emitting species are determined will be discussed; a full list of wavelengths of band heads and other data are given in the Appendix. These descriptions of the systems will be followed by sections in which the effects of fuel type, mixture strength and other flame conditions on the spectra are dealt with. A discussion of the processes of formation and excitation of the various radicals and of their role in the combustion reactions will be left to Chapters VIII and X.

Diffusion-flame structure for a two-step chain reaction

Abstract: The low-speed combustion of initially unmixed gaseous reactants under an irreversible two-step chain reaction is examined. Both equilibrium burning, in which two spatially separated flames of zero thickness arise, and near-equilibrium burning, in which two spatially separated flames of small but finite thickness arise, are studied by limit-process expansion techniques. Two time-dependent flows are examined: the first is (one-dimensional) transient mixing flow; and the second is (two-dimensional) transient counterflow. The latter flow, in which there is an impressed finite strain parallel to the flame, such that the flame itself is longitudinally stretched, is discussed as elucidating the characteristics of combustion in non-equilibrium turbulent shear flow.

On the oxidation of fuel nitrogen in a diffusion flame

Abstract: The kinetic mechanisms of fuel nitrogen conversion to NO and N2 in a diffusion flame were investigated. A simple model of a diffusion flame in which the reaction zone has a finite thickness was developed. The purpose of this model was to allow the testing of complex kinetic mechanisms of pollutant formation under conditions where the fuel and oxidant feed rates are controlled by diffusion. A simple kinetic mechanism in which fuel nitrogen was simulated by nitrogen atoms showed the correct functional dependence of nitric oxide emissions on fuel nitrogen content. The model also predicts a significant effect of combustion intensity and temperature on fuel nitrogen conversion. For the hydrogen air diffusion flame the Zeldovich reaction mechanism could account for the production of N2 as well as NO.

Determination of Trace Metals in Crude oils by Nonflame Atomic Absorption Spectroscopy

Abstract: Determination of trace metals, Co, Mg, Na, Sn, Cd, Zn, and Al in crude oil by nonflame atomic absorption spectroscopy with a modified carbon rod atomizer was studied. A standard addition method was developed for determination of these elements. The results obtained for three of the seven elements studied were confirmed by a conventional flame spectroscopic technique. Sensitivity and detection limit data were obtained for each element studied. Sensitivities ranged from 5.1 × 10−13 g for Mg to 1.5 × 10−10 g for Al. Detection limits ranged from 1.6 × 10−13 g for Mg to 2.8 × 10−11 g for Al. The effect of different sheath gases and a hydrogen diffusion flame on the absorbance was also studied. Sn and Al showed a relatively strong dependence on the hydrogen diffusion flame. Depressions of the absorbance signals were observed in some cases when the analyte elements were determined in the presence of large excesses of certain metals. These depressions were probably due to the analyte elements being dispe...

Studies on the Flame Structure of a Spray Burner : 1st Report, Measurement of Quantities Related to Droplets and Gas within the Flame, and Their Correlations

Abstract: To clearify the flame structure of a spray burner, distributions of droplets, and those of temperature, flow velocity and gas composition were measured within the flame of an air-atomizing burner. The magnesium oxide method providing a shutter mechanism was adopted to detect the droplets. To measure the gas temperature, a suction pyrometer free from the effect of droplets was specially desined. The following were concluded. (1) The flame may be simplified as a model consisting of three regions. Designating them as A, B and C in order of distance from the burner nozzle, A is a region where a heterogeneous mixture containing many droplets is burning; in B, only a combustible gas fed from A is burning continuously; in C, its remainder is burning intermittently. (2) It can be assumed that the droplets in A do not burn individually, but fuel vapor evaporated from them collects and burns like a gas diffusion flame.

The jet engine design that can drastically reduce oxides of nitrogen

Abstract: The NOx pollution problem of hydrogen fueled turbojets and supersonic combustion ramjets (scramjets) was investigated to determine means of substantially alleviating the problem. Since the NOx reaction rates are much slower than the energy producing reactions, the NOx production depends mainly on the maximum local temperatures in the combustor and the NOx concentration is far from equilibrium at the end of a typical combustor (L approximately 1 ft). In diffusion flames, as used in present turbojets and scramjets combustor designs, the maximum local temperature occurs at the flame and is equal to the stoichiometric value. Whereas, in the heat conduction flames, wherein the flame propagates due to a heat conduction process away from the flame to the cooler oncoming premixed unburnt gases, the maximum temperature is lower than in the diffusion flame. Hence the corresponding pollution index is also lower.

Interaction of gaseous multiple swirling flames.

Abstract: This thesis is based on a study of the behaviour of the multiple burner systems. The influence of number of burners, their separation and degree of swirl on the interaction of multiple gaseous turbulent diffusion flames, for different configurations chosen, has been investigated. A single flame has been studied as a reference flame to provide information for the comparison with multiple systems. The temperature and concentration profiles within the flames have been determined using thermocouples and a semi-continuous gas sampling system in conjunction with a gas chromatograph. Three orthoganol mean velocity components in the annular air stream of a single isothermal swirling jet have been measured using a hot wire anemometer and by the application of a four point measurement technique developed within the department. Multiple flame systems were found to be less stable against blow-off compared to single flames and the blow-off limit shifted towards the fuel rich region as the swirl was reduced. At low swirl levels and minimum separation the centre flames were lifted off the burner rim and were frequently blown-off.

Combustion of gas mixtures with particles

Abstract: A multivelocity and multitemperature model, with heterogeneous chemical reactions, is used to describe the motion of such media. The article gives expressions characterizing the force, thermal, and mass interaction between the phases. A study is made of the problem of the normal propagation of the flame front inthe gas suspension for the case when the combustion of the particles takes place in the condensed phase. The values obtained for the rate of propagation of the flame front are given as a function of several parameters which determine the process under investigation (particle size, composition of the mixture, etc.). An analysis of the experimental data permits the isolation of three limiting sets of conditions for combustion of the particles. In the first place, purely heterogeneous conditions, when the chemical reaction takes place directly within or on the surface of the particles (in the condensed phase) and, by the same token, the heat of the chemical reaction is evolved directly in the condensed phase. For example, particles of graphite or carbon, which contain no volatile substances, burn in this way. In the second place, quasihomogeneous conditions, when combustion and heat evolution take place over the whole volume of the gas phase after vaporization and mixing of the fuel vapors with an oxidizer. Sufficiently fine particles of an easily vaporized fuel burn in this fashion. In the third place, vapor-phase conditions, when combustion and direct heat evolution take place in thin layers of flames surrounding the particles. These layers of flame have a considerably higher temperature than the surrounding gas and the particles. With regard to the combustion of a mixture with solid particles, the problem of the normal propagation of a flame front in a single-velocity and single-temperatu re approximation has been discussed by O. I. Leipununskii [1]. Papers [2, 3], for the case when the temperatures of the gas and the particles differ, discuss the combustion of a gas suspension under purely heterogeneous combustion conditions. Flame propagation in a gas suspension of an easily vaporizing fuel was studied experimentally by Burgoyne and Cohen [4]. They observed that, with an increase in the particle size, the quasi-homogeneou s conditions go over into vapor-phase conditions. In such mixtures, for quasi-homogeneou s conditions, the problem of the propagation of the flame front in its simplest form is investigated in the article of Williams [5].

The Carbon Monoxide Flame

Abstract: The flame of carbon monoxide burning with air or oxygen is bright blue, and the spectrum consists of a strong continuum with a weak system of numerous narrow bands superposed on it. The emission is strongest in the blue to near ultra-violet, 4500–3500 A, but extends from the near infra-red to well down in the ultra-violet below 2400 A. The banded part of the spectrum is clearest in the visible and becomes increasingly masked by the continuum at shorter wavelengths.

Measurements of Effective Temperature and Studies with Special Sources

Abstract: In the three preceding chapters, observations on the emission and absorption spectra of normal stationary flames have been described. In this chapter we shall be concerned with additional observations aimed at elucidating the detailed state of the gases in the reaction zone. These will include quantitative measurements on the relative intensities of lines and bands, or on the contours of individual lines, with the results expressed as effective temperatures. The various methods of measuring flame temperatures have been described fully in the recent edition of Flames (Gaydon and Wolfhard, 1970); here the principles of the methods will be referred to only briefly, but results will be given. Other observations in special sources such as flash photolysis, atomic flames and shock tubes, and also tracer observations using stable isotopes for the study of flame spectra, give information about basic chemical processes and excitation mechanisms and are relevant to the understanding of flame spectra. Work on some special flames, such as those supported by fluorine instead of by oxygen, is also valuable for a discussion of the reaction and excitation processes in normal flames and is therefore included here.

Flame Structure and Reaction Processes

Abstract: In the preceding chapters I have concentrated on observations relating to the spectra of flames and related sources. Now the time has come to talk of many things, in fact to “stick my neck out” and give my opinions on the interpretation of the observations and their bearing on theories of chemical reaction processes in flames and on the detailed structure of the reaction zone. As usual, the arrangement of the chapter is similar to that in the previous edition, but ideas have matured considerably and this has led to much detailed revision.