Hydrogen-oxygen Diffusion Flame Research Articles

Zn-doped TiO2 nanoparticles with high photocatalytic activity synthesized by hydrogen–oxygen diffusion flame

Zn-doped TiO2 nanoparticles with high photocatalytic activity were synthesized by the hydrogen–oxygen diffusion flame method and the photocatalytic degradation mechanism of rhodamine B dye under visible light irradiation were elaborated. The Zn dopants presented in the form of small ZnO nuclei dispersing randomly on the surface of anatase TiO2 nanoparticles. It is found that the photosensitized degradation activity can be enhanced by doping an appropriate amount of Zn. The improved activity by Zn doping can be attributed to the appropriate energetic position between ZnO and the excited state of dye, which enhanced the electron injection into the conduction band of TiO2 by capturing electron, subsequently promoted the formation of reactive oxygen species. Hence, the enhanced photodegradation of dyes under visible irradiation can be realized.

Experimental and numerical analyses of magnetic effect on OH radical distribution in a hydrogen-oxygen diffusion flame

The effect of magnetic field on OH radical distribution in a hydrogen-oxygen diffusion flame was experimentally and numerically investigated to explore the possibility of combustion control by magnetic force. In experiments, a coaxial type of burner was set between the magnet pieces. Two-dimensional (2D) cross-section distributions of OH* chemiluminescence intensity and OH fluorescence intensity were obtained with spectroscopic techniques using a CCD camera and a Planar Laser-Induced Fluorescence (PLIF) system, respectively. It was clearly seen that the high-density regions of OH* and OH radicals axisymmetrically migrated toward the central axis of the flame due to the influence of the magnetic field. In numerical simulations, such a phenomenon was qualitatively reproduced by solving the equations of reactive gas dynamics and magnetism. As a result, it was found that the magnetic force does not directly and selectively induce the diffusion velocity (the relative velocity) of OH itself. Alternatively, the magnetic force acting on O 2, whose mass density and magnetic susceptibility are much larger than those of other chemical species, causes the change in the mean velocity (the mass-average velocity) of mixture gas to transport the OH radical distribution indirectly and passively.

Numerical analysis of a hydrogen-oxygen diffusion flame in vertical or horizontal gradient of magnetic field

The magnetic force is essentially in proportion to the mass density and the magnetic susceptibility of paramagnetic chemical species and the gradient of magnetic field. In this study, the effect of magnetic field on OH radical distribution in a hydrogen-oxygen diffusion flame was investigated by numerically solving the equations of reactive gasdynamics and magnetism to explore a possibility of combustion control by magnetic force. Particularly, we attempted the analysis for three kinds of cases with different spatial distributions of the magnetic field: Case 1 is without the magnetic field, Case 2 is under the vertical gradient of magnetic field, and Case 3 is under the horizontal gradient of magnetic field. According to the analysis, because the mass density and the magnetic susceptibility of O 2 are much larger than those of other chemical species in the peripheral region of the flame, O 2 was strongly influenced by the magnetic force in that region. Consequently, this force induced the flow of gas including a large amount of O 2 and indirectly changed the OH distribution in the flame. The horizontal magnetic gradient (Case 3) was about 1.2 times more effective in the OH density change than the vertical gradient (Case 2).

火炎による酸化ゲルマニウム微粒子生成

The formation and growth mechanisms of germanium oxide ultrafine particles in a flame were experimentally investigated by means of TEM observation. GeO particles were initially formed at the lower part of the hydrogenoxygen diffusion flame and then evaporated as the temperature increased in the flame. In case of low concentration of raw materials, GeO particles was entirely evaporated and then appeared again as GeO2 particles through homogeneous nucleation. On the otherhand, in case of high concentration of raw materials, developed aggregates of GeO particles were oxidized from the peripheral portion accompanied by shrinkage due to the evaporation of the GeO.The formation and growth mechanisms of ultrafine particles in a flame were discussed by comparing germanium oxide particles with the silica particles reportted in the literature.

Construction of a mass spectrometer for sampling ions from diffusion flames

This paper describes the construction and calibration of a mass spectral system for investigation of ions produced in diffusion flames. Use of Ni-63 as a source for the ionization of nitrogen gas confirmed calibration in the low end of the spectrum. Ions, collected from a normal hydrogen-oxygen diffusion flame and from one containing methane, were shown to correlate with those that have been observed previously in similar flames. The system's unique adjustable burner head permitted ion sampling of a hydrogen atmosphere flame at various positions above the flame. This is the first report of the ions produced in such a flame. Water clustered hydrogen ions as large as (H 2O) 5H + were observed 7 cm above the hydrogen atmosphere flame.

An apparatus for manufacturing flexible fused silica columns for gas liquid chromatography. Part I. The drawing process

A compact description is given of a simple and reliable method of drawing flexible fused silica capillary for gas chromatography. Some emphasis is given to the fact that the practices of drawing optical fibres should not be followed too slavishly so this leads to unnecessarily complicated and expensive equipment. Satisfactory capillary column silica tubing can be made with straightfoward extension of the method developed earlier for drawing thick walled capillary. A simple glass/silica hydrogen oxygen diffusion flame bumer is described for fusing the preform tubing at the draw point which is enclosed by a water cooled glass enclosure to trap evaporated silica and maintain the operation under dust free conditions. The uniformity of the capillary diameter is better than 5% which is adequate for most gas chromatographic purposes. The second part of the paper yet to be published will cover the methods developed for coating the capillary both internally and externally.

The Transition to Instability in a Steady Hydrogen-Oxygen Diffusion Flame

Abstract —Blow-off of a streamwise diffusion flame does not usually show features intermediate between those characteristic of the burner-attached flame and a quasi-stable lifted flame. The present work has, however, characterised an unusual intermediate stage in the blow-off of a lean hydrogen-oxygen diffusion flame, where the flame base takes on a stable cellular structure. From previous work, it is known that, near extinction, there is transfer of fuel through the base of the flame into the oxidant stream. The partial premixing resulting from such inter-stream transfer gives rise in the particular case of this lean flame to a composite premixed/diffusion flame structure at the flame base which is most probably responsible for the cellularity.

Analysis of a laminar flat plate boundary-layer diffusion flame

A numerical analysis of a laminar hydrogen-oxygen diffusion flame in a flat plate boundary layer was carried out in order to investigate its non-equilibrium and close-to-equilibrium structure at various positions in the boundary layer. Variable properties including thermodiffusion and 15 elementary reactions between 8 species were used in the calculation. The results show the ignition and non-equilibrium development of the flame and the approach to local chemical equilibrium within the flame zone. On both sides of the flame zone, due to the low temperatures there, the chemical reactions are practically frozen even at large distances from the leading edge.

Numerical analysis of a non-equilibrium turbulent free jet diffusion flame

The non-equilibrium flowfield of a turbulent free jet hydrogen-oxygen diffusion flame is numerically analyzed. Turbulent transport properties are described by an eddy viscosity formulation. An elaborate finite-rate chemistry model is utilized and the reaction mechanism adopted for the analysis considers 23 elementary reactions between 9 chemical species (H 2, O 2, H, O, OH, H 2O, HO 2, H 2O 2 and O 3). The governing set of non-linear partial differential equations is solved by an explicit finite-difference procedure. Predictions of velocity, temperature and mass fractions of chemical species in the flowfield are obtained. Calculated effective speeds of the elementary reactions demonstrate the important role of the chemical species HO 2, H 2O 2 and O 3 in the chemical process, particularly in the relatively cold oxygen-rich regions of the flame. Significant deviations are observed in the temperature and mass fraction profiles when a simplified model for the reaction mechanism without the appropriate HO 2-, H 2O 2- and O 3-reactions is employed.

The Hydrocarbon-induced Fluorescence of Atoms in Flames

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 process[Formula: see text]as the origin of the energy of excitation.

The effect of the large hydrogen dissociation activation energy on an equilibrium-broadened hydrogen-oxygen diffusion flame

The structure of a hydrogen-oxygen diffusion flame under equilibrium conditions is dominated by the influence of the equilibrium constant for the hydrogen dissociation-recombination reaction. An attempt to continue a previous solution, which used the method of matched asymptotic expansions, to higher orders of approximation led to difficulties of a numerical kind as a result of the large rate-of-change of this equilibrium constant with temperature. It is shown how the matter can be resolved by using the asymptotic expansion method with the small parameter (reciprocal of the equilibrium constant) treated as a function of temperature; the solutions follow from a simple iterative procedure.