Diffusion flame

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

Entrainment and Flame Geometry of Fire Plumes

Abstract: This study concerns the flame structure and fire plume entrainment of natural gas diffusion flames on 0.10, 0.19 and 0.50 m. diameter burners. The heat release rates ranged from 10 kW to 200 kW. Flame heights based on high speed photography and eye averages show a transition in the dependence of flame height on a dimensionless heat addition parameter around unity. For flames taller than three burner diameters, the initial diameter of the fire does not affect the length of these flames whereas for short flames initial geometry becomes important. Another prominent feature of these flames is the presence of large scale ring vortex-like structures which are formed close to the burner surface more or less regularly. It is found that these structures are responsible for the fluctuations of the flame top. Entrainment measurements spanned heights starting very close to the burner surface to distances about six times the average flame heights. Experiments indicate the presence of three regions; a region close to the burner surface where plume entrainment rates are independent of the fuel flow (or heat release) rates; a far field region above the flame top, where a simple point source model correlates the data reasonably well; and a not so well-defined intermediate region where entrainment seems to be similar to that of a turbulent flame with plume-like characteristics. It is also found that the disturbances in the ambient atmosphere will greatly enhance the fire plume entrainment. Finally, a theoretical study of a steady, buoyant, diffusion flame indicated the importance of the puffing in the entrainment process.

Structure of a high Karlovitz n -C 7 H 16 premixed turbulent flame

Abstract: Results from a series of direct numerical simulations (DNS) of a high Karlovitz, slightly lean (ϕ=0.9ϕ=0.9), n-C_7H^(16)/air premixed turbulent flame are presented. The flame is statistically flat and is subjected to an inflow of homogeneous isotropic turbulence. A 35-species and 217-reaction mechanism (Bisetti et al., 2012) [17] is used to represent the chemistry. Two simulations have been performed: one with unity Lewis number to asses the effects of turbulence on the flame structure in the absence of differential diffusion, and the other with non-unity Lewis numbers to analyze how turbulence affects differential diffusion. The Karlovitz numbers are 280 and 220 respectively. The first simulation reveals that the flame is strongly affected by turbulence as enhanced mixing largely thickens the preheat zone. However, the turbulent flame structure (i.e. the correlation between species and temperature) is similar to that of a one-dimensional flat flame, suggesting that turbulence has limited effect on the flame in temperature space, in the absence of differential diffusion. In the second simulation, the flame structure is affected by turbulence, as differential diffusion effects are weakened. It is suggested that this result is attributed to the fact that turbulence drives the effective species Lewis numbers towards unity through an increase in effective species and thermal diffusivities. Finally, the reaction zones of both the unity and the non-unity Lewis number turbulent flames remain thin, and are locally broken (only to some extent for the unity Lewis number flame, and more strongly for non-unity).

Two-color laser-induced incandescence (2C-LII) technique for absolute soot volume fraction measurements in flames

Abstract: A two-color version of the laser-induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in flames By using a calibrated tungsten ribbon lamp, soot peak temperatures were measured as a function of fluence at several locations in an ethylene diffusion flame by using a steeply edged laser beam profile Above a certain fluence threshold, peak temperatures were tightly distributed just above 4000 K independent of the particle size and number density Radial profiles of soot volume fraction were obtained and compared (not calibrated) with results from the laser extinction technique Good agreement showed the validity of the 2C-LII technique at a controlled fluence