Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

Effects of Oxygen on Soot Formation in Methane Diffusion Flames

Abstract: The effect of small additions of oxygen to the fuel on formation of soot in methane-air diffusion flames was studied over a range of flow rates and of burner diameters. The flames studied were shorter than those of previous studies, purely blue or blue and yellow without soot escape. Heights of various distinctive features were measured, and composition and temperature profiles were obtained; the distinctive features include.onset and termination of visible emission of radiation and deposition of material on a quartz filament inserted into the flame. The results indicate negligible influences of oxygen addition and thereby suggest that ions from the primary mechanism CH+Orarr;CHO++e- are unimportant in soot formation in these flames. A simplified one-step kinetic model accounting for buoyancy and momentum was developed and employed to obtain estimates of overall rate parameters for flame attributes related to soot formation.

On the behavior of premixed flames in a rotating flow field: Establishment of tubular flames

Abstract: The behvior of premixed flames in a rotating flow field has been investigated using a swirl type burner, in which a fuel/air mixture is ejected tangentially into a cylindrical combustion chamber. The results show that for appropriate conditions for the ejection velocity and the fuel concentration of the mixture, a tubular flame of circular cross-section is established inside the burner. By this flame front, the combustion field is separated into two regions, an outer unburned gas region and an inner burned gas region, and the burned gas flows inside the flame with rotation. This rotating hot gas core is very stable according to the Rayleigh stability criterion. However, further experiments show that this type of tubular flame can be established for lean methane/air or hydrogen/air mixtures, but not for lean propane/air mixtures. In the former case, the diameter of the flame decreases with a decrease of the fuel concentration, and the flame is eventually extinguished after the tubular flame is merged into a luminous rod, whereas in the latter case, an unsteady, corrugated flame is established around the wall of the cylindrical burner, and the flame is extinguished without forming a uniform flame front. The fuel concentration at the extinction limits is close to the lean flemmability limit in the former case, whereas very far from that in the latter case. These two distinct behaviors of flames in the rotating flow field have been discussed on the basis of the tangential velocity distribution of the Rankine's combined vortex and the flame stretch theory considering the Lewis number effect.

Time-resolved laser-induced incandescence and laser elastic-scattering measurements in a propane diffusion flame

Abstract: Laser-induced incandescence (LII) and laser elastic-scattering measurements have been obtained with subnanosecond time resolution from a propane diffusion flame. Results show that the peak and time-integrated values of the LII signal increase with increasing laser fluence to maxima at the time of the onset of significant vaporization, beyond which they both decrease rapidly with further increases in fluence. This latter behavior for the time-integrated value is known to be characteristic for a laser beam with a rectangular spatial profile and is attributed to soot mass loss from vaporization. However, there is no apparent explanation for the corresponding large decrease in the peak value. Analysis shows that the peak value occurs at the time in the laser pulse when the time-integrated fluence reaches approximately 0.2 J/cm2 and that the magnitude of the peak value is strongly dependent on the rate of energy deposition. One possible explanation for this behavior is that, at high laser fluences, a cascade ionization phenomenon leads to the formation of an absorptive plasma that strongly perturbs the LII process.