Diffusion flame

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

Emission spectroscopy of flame fronts in aluminum suspensions

Abstract: Spatially resolved emission spectra from Bunsen-type flames stabilized in aluminum suspensions in air and oxygen–argon/helium mixtures were obtained using a mechanical-optical scanning system. A low resolution (1.5 nm) spectrometer was used to acquire the broad spectra over the 350–1000 nm range, and a high-resolution (0.04 nm) instrument was used for observation of AlO molecular bands and non-ionized atomic aluminum. The temperature of condensed phase emitters in the flame was derived using polychromatic fitting of the continuum spectra to Planck’s law. AlO temperature was found by fitting of the theoretically calculated shape of the band to experimental data. Peak temperatures of the condensed emitters were found to be approximately 3250 K in aluminum-air flames and approximately 3350 K for oxygen–argon/helium flames. Temperatures derived from AlO spectra coincide with the temperature of the condensed emitters with measurement accuracy and are only 100–200 °C lower than the computed equilibrium flame temperatures. The radial distribution of the temperature profile of the continuous emitters was found via Abel deconvolution and recovered the double-front structure of the Bunsen flame cone, with the outer flame being attributed to a diffusion flame of the fuel-rich products with ambient air. The observation of atomic aluminum lines seen in emission from the outer flame edge and partial self-absorption from the inner flame confirms the structure associated with the double-front structure. The implications of these results for the regime of particle combustion in a dust flame are discussed.

Cluster size distribution for free molecular agglomeration

Abstract: Dobbins and Megaridis have observed soot agglomerates in a diffusion flame via thermophoretic sampling. The agglomerates are made up of spherules with a typical diameter of about 30 nm. A characteristic of the agglomerate is the relatively low density of the structure with much open space. This study is concerned with modeling the agglomeration growth process.

Soot formation and temperature field structure in co-flow laminar methane–air diffusion flames at pressures from 10 to 60 atm

Abstract: The effects of pressure on soot formation and the structure of the temperature field were studied in co-flow methane–air laminar diffusion flames over a wide pressure range, from 10 to 60 atm in a high-pressure combustion chamber. The selected fuel mass flow rate provided diffusion flames in which the soot was completely oxidized within the visible flame envelope and the flame was stable at all pressures considered. The spatially resolved soot volume fraction and soot temperature were measured by spectral soot emission as a function of pressure. The visible (luminous) flame height remained almost unchanged from 10 to 100 atm. Peak soot concentrations showed a strong dependence on pressure at relatively lower pressures; but this dependence got weaker as the pressure is increased. The maximum conversion of the fuel’s carbon to soot, 12.6%, was observed at 60 atm at approximately the mid-height of the flame. Radial temperature gradients within the flame increased with pressure and decreased with flame height above the burner rim. Higher radial temperature gradients near the burner exit at higher pressures mean that the thermal diffusion from the hot regions of the flame towards the flame centerline is enhanced. This leads to higher fuel pyrolysis rates causing accelerated soot nucleation and growth as the pressure increases.

Enthalpy diffusion in multicomponent flows

Abstract: The enthalpy diffusion flux in the multicomponent energy equation is a well-known yet frequently neglected term. It accounts for energy changes associated with compositional changes resulting from species diffusion. The term prevents local violations of the entropy condition in flows where significant mixing occurs between species of dissimilar molecular weight. In simulations of nonpremixed combustion, omission of the enthalpy flux can lead to anomalous temperature gradients, which may cause mixing regions to exceed ignition conditions. The term can also play a role in generating acoustic noise in turbulent mixing layers. Euler solvers that rely on numerical diffusion to blend fluids at the grid scale cannot reliably predict temperatures in mixing regions. On the other hand, Navier–Stokes solvers that incorporate enthalpy diffusion can provide much more accurate results. In constructing turbulence closures for high Reynolds number mixing, the same turbulent diffusion model that appears in the species mas...