Showing papers on "Laminar flame speed published in 1972"

Diffusion flame in homologous turbulent shear flows.

Abstract: The simplified statistical theory developed previously is employed to analyze the equilibrium and near‐equilibrium combustion of initially unmixed reactants. It is found that the flame zone in the limit of large Damkohler numbers is very thick and is of the order of the local integral scale of turbulence. This is in contrast to the existing phenomenological theories which predict the infinitesimally thin flame sheet, in the same limit, as it is with the laminar diffusion flame. Qualitative agreements with the available experimental results are shown. It is found that singularities exist at the edges of the flame which are removed as Damkohler number is reduced. Also, it is found that the heat transfer may take place against the local mean temperature gradient in certain regions within the flame.

Method for flame bonding by use of high velocity,high temperature direct flame

Abstract: A METHOD AND APPARATUS FOR OBTAINING RAPID BONDING OF THERMOPLASTIC MATERIALS TO THEMSELVES OR OTHER SIMILAR OR DIFFERENT MATERIALS BY THE USE IOF A HIGH VELOCITY, HIGH TEMPERATURE DIRECT FLAME IN COMBINATION WITH PRESSURE. THE METHOD IS SUFFICIENTLY RAPID SO THAT THE PROPERTIES OF THE MATERIALS ARE NOT SUBSTANTIALLY DETRIMENTALLY AFFECTED. THIN LAMINATES OF HIGHLY ORIENTED MATERIALS CAN BE BONDED WITHOUT LOSS OF STRENGTH CHARACTERISTICS.

Turbulent Flame Velocities In Premixed Sprays Part II. Theoretical Analysis

Abstract: The process of propagation of a turbulent flame into a premixed spray has been studied theoretically In general, the flame velocity of a premixed flame is presented theoretically as the eigenvalue of a set of differential equations In this study, a numerical method was adopted in determining the flame velocity as an eigenvalue, so that a theoretical analysis on a rather realistic model, where the droplet size distribution, the temperature dependences of thermal or transport properties and some other factors were taken into account, was possible This treatment successfully explained the observed behavior of premixed spray flames in terms of the intensity of turbulence, average droplet diameter and volatility of the fuel The predicted dependence of the flame velocity on the fuel-air ratio, however, was found to be weaker than the observed one, but this may be explained by the fact that the amplifying effect of the flame on the turbulence level varies with the fuel-air ratio It was also found t

Streamline Deflection by a Diffusion Flame

Abstract: The results of experimental and theoretical studies of streamline deflection in diffusion flames are presented for approximately streamwise flames stabilised on a Parker-Wolf hard burner. It is shown that both the displacement of the dividing streamline from the flame sheet and the phenomenon of streamline refraction through the flame sheet can be predicted at least qualitatively by a simple linearised model for the diffusion flame in Oseen flow, in which only the irrotational pressure, temperature and composition waves are considered. Although this treatment involves the description of flame properties in terms of disturbances from freestream values, essentially the same results are obtained by linearisation about flame sheet properties. The question is left open whether the present mechanism for streamline refraction is that which leads to transfer of fuel or oxidant across the base of the flame close to extinction, eventually leading to flame lift and complete extinction.

The One-dimensional Diffusion Flame in a Two-Dimensional Counter-Flow Burner

Abstract: A counter-flow burner has been used to stabilize one-dimensional diffusion flames of a large size, and temperature treasurements on these flames have been made by the “deflection method.” The distance between the stagnation point and the flame shows a discontinuity when the velocity gradient along the flame reaches a critical value e tr [1] and there is a corresponding discontinuity in the temperature. Analysis of experimental results indicates that, though the ratio of oxygen to fuel mass flux into the flame front is held constant below this value it shifts towards more fuel rich ratios when e tr is exceeded. This can be ascertained from the measured concentrations of combustion products around the flame front. Furthermore, a kinetic analysis of the flames indicates that such discontinuities are to be expected.

Amplification of Turbulence Level by a Flame and Turbulent Flame Velocity

Abstract: In turbulent combustion, the existence of turbulence increnses the flame velocity markedly, while the flame augments the intensity of turbulence. A consideration of this interaction between a flame and the aerodynamics (turbulence) has led to a set of equations from which turbulent flame velocities can be calculated with reasonable accuracy over a wide range of conditions. They consist of the Karlovitz's equation on turbulent flame velocity and an equation expressing the amplifying effect of a flame on the turbulence level, and they were found to fit the various types of flame fairly well from confined turbulent flames to open burner flames like Bunsen or V -shaped flames, regardless of the burner size or the fuel type. The results are: (1) the extent of turbulence amplification depends both on the initial intensity of turbulence and on the difference between the kinetic energies of the gas before and behind the flame front, (2) viscous attenuation of turbulence level because of the high viscosity of the burning gas cannot be ignored, (3) the size of the combustor or burner as well as the scale of turbulence is an important factor affecting the amplifying effect of the flame on turbulence level, and (4) when the burner size or the turbulence scale increases, the extent of turbulence amplification also increases.