Flame Angle Research Articles

Flame propagation in grid-induced turbulence

The interaction of grid-generated turbulence with premixed, V-shaped ethylene/air flames has been studied using laser Doppler anemometry and Rayleigh scattering as optical diagnostics, respectively, for the streamwise component of elocity and the density. Turbulent flame propagation was studied for three upstream flow velocities, U ∞ = 245, 500, and 684 cm/s with fuel/air equivalence ratios ranging from 0.55 to 0.75. The angle of the flame with the flow axis was varied from 12° to 24°. Profiles of mean values and the turbulence intensity of velocity and density were obtained through the flame. For all conditions, the turbulence intensity of velocity was observed to decrease behind the flame, indicating the dominance of dilatation effects. In addition, profiles of the mean streamwise velocity component indicate streamlines to be significantly deflected at the flame for the case of the most oblique flame. For the conditions in which the flame angle was 12°, the wake of the flame holder dominates the flow field behind the flame and vortices are observed. This suggests that results for these conditions are not typical of the interaction of a flame with grid-induced turbulence. Probability density functions of Rayleigh scattering in the flame and turbulent intensities indicate that intermediate states of chemical species are likely to be significant in determining density statistics.

On the safety of wears against disaster

This study aims to find a flammability of general textiles and flame-proof textiles.1) Safety of flame-proof finished natural clothes is more safety than flame-proof finished union clothes were blended with synthetic fibers.2) The density of flame-proof finishing bath need not be deeps as standard density in case of union clothes were blended with synthetic fibers and natural fibers.3) Flammability of some union clothes was different between flame angle or flame course.4) Safety of flame-proof polyester is noticeably different from phenol fabric on account of flame behaviour.5) Safety of wears should be made synthetically on safety against flame touch, combustibles stick and heat transfer.

Premixed flame propagation characteristics in a supersonic airstream

Measured values of flame angles are presented to aid the design of premixed combustion chambers and prediction of flame propagation. Flame spread, velocity, and dependence of burning rate on the properties of unburned flow and on turbulence levels are compared with the measured values. The premixed flame angle is found proportional to the amount of heat released, and correlates readily with the fuel mixture ratio through the rate of heat release or rate of water formation. Finite rate combustion affects flame angle mostly at off-stoichiometric conditions. The pilot affects the flame angle if abundant unburnt fuel is present in the pilot hot gases. Viscosity runs several times over the rated level.

A comment on the flame angle, double-burner technique of determining flammability limits

The interaction between inner and external coaxial flames is experimentally investigated in detail. The minimum equivalence ratio t of CH4-air premixtures (test premixtures) for complete combustion is measured as a function of the flow rate by the use of a small pilot flame whose equivalence ratio, p is equal to unity or less. The minimum t is dependent upon p and the flow rate of the test premixture. The effects of radial and axial separations of the two flames are also investigated with the use of three types of burner ports. The existence of diffusive and convective mixing of the two flows on a coaxial burner is proved. The magnitude of the mixing is estimated by a numerical calculation. A small amount of mixing plays an important role in stabilizing the flame in a highspeed flow of the lean premixture. It is concluded that the use of a coaxial burner for the measurements of the flammability limits is invalid.This paper also discusses the merit of simple coaxial burners without any thermal feedback or recirculating flow flow for lean premixture combustions. The overall minimum equivalence ratio attained by the present experiments is 0.6 at a mean flow velocity of 5.3 m/sec.

A model study of wind-blown free-burning fires

In a study of free-burning fire modeling, both point- and area-source flames and line, fires were exposed to cross winds. With point- and area-source flames, the flame height was found to decrease slowly with the initial exposure to the cross wind and then to decrease more rapidly as the velocity of the cross wind was increased. Specifically, the dimensionless, flame height varied with the negative 1/4-power of the Froude number based on cross-wind velocity and undisturbed flame height, above a Froude number of 0.2. The horizontal extension of the flame, on the other hand, increased rapidly with increasing cross wind at first, and then less rapidly with the 1/6-power of the Froude number. When line fires composed of point sources were exposed to cross winds, the height of the flame varied with the inverse square root of the Froude number plus a constant, the value of which depends on the fuel. The tangent of the flame angle varied directly with the square root of the Froude number. These observations agree generally with those reported in the literature relative to two-dimensional fires from wood cribs, up to a value of the Froude number at which buoyancy effects on the flame seem to vanish.

Structure and Properties of Alloys in the Vanadium-Tungsten System

in that no separate method of determining the nature and concentration of active transient combustion intermediates is employed. It is quite possible that some extension of the work, in which the data reported here might readily be used, would lead to an indication of the mean lifetime of the active radicals. It is possible, of course, that this was considered in other papers by these authors which are listed as references in this one. The method used for measuring the flame speed is of some passing interest. The upright wedge has been used in the United States and other Western countries for years, as well as in Russia. The inverted wedge method has also been used, although it must be conceded that when this method is applied to an ordinary Bunsen burner there are effects on the flow owing to the presence of the flame that tend to confuse the simple theory relating the flame angle with the flame speed. It would appear that the experiments reported here are also subject to that criticism. As the authors point out, the purpose of comparing flame speeds with and without the presence of active radicals is served without the necessity for a correction of the flame speed measurements for the distortion of the flow resulting from the flame.

The effect of flame configuration on combustor performance

The effect of flame configuration on combustor performance is analysed theoretically by assuming that chemical conversion commences when the premixed gaseous propellants pass through the flame surface. Hence the percentage conversion, which is indicative of performance, can be determined at any point downstream of the flame surface by considering the chemical law of mass action and assuming an integral order of reaction. Integration over the cross section of the combustor then yields the theoretical performance for any selected length of combustor. As could be expected, performance increases as the flame angle increases, and flame configurations resulting from annular flameholders are more efficient than the conventional V-gutter of conical flameholders. Qualitative confirmation of the trends, predicted theoretically, is provided by experimental data obtained from a 2 in. i.d. burner.

Design and Operating Problems With Gas- and Oil-Fired Boilers for Stand-By Steam-Electric Stations

Abstract The problem of stand-by operation, although not new on the Pacific coast, is a comparatively new experience for large units operating at pressures above 400 lb and temperatures above 700 F. With combination gas and fuel-oil installations, there are more difficulties to overcome with fuel oil than with gas. The paper describes problems in the control of flame angle when burning fuel oil and developments in high-speed automatic combustion control which make possible the acceptance of emergency loads from 5 to 90 per cent of turbogenerator capacity as fast as the turbine governors can open the control valves. Various operating procedures which have been developed as a necessary routine to meet stand-by conditions are also described. The essential requirements for stand-by and base-load operation are compared. Descriptions are given of actual load-pickup tests on a 1400-lb, 750-F reheat plant and a 425-lb, 750-F plant, and the actual events which take place in the first few seconds of an emergency load pickup are analyzed from the standpoint of what should be provided for in the design of boiler storage capacity, and speed of combustion control. Statistics relating to these features are given for four plants on the Pacific Coast.