Effects of Burner Configurations on the Natural Oscillation Characteristics of Laminar Jet Diffusion Flames

Abstract

In this work, effects of burner configurations on the natural oscillations of methane laminar diffusion flames under atmospheric pressure and normal gravity conditions have been studied experimentally. Three regimes of laminar diffusion flames, namely, steady, intermittent flickering and continuous flickering have been investigated. Burner configurations such as straight pipe, contoured nozzle and that having an orifice plate at the exit have been considered. All burners have the same area of cross section at the exit and same burner lip thickness. Flame height data has been extracted from direct flame video using MATLAB. Shadowgraph videos have been captured to analyze the plume width characteristics. Results show that, the oscillation characteristics of the orifice burner is significantly different from the other two burners; orifice burner produces a shorter flame and wider thermal plume width in the steady flame regime and the onset of the oscillation/flickering regimes for the orifice burner occurs at a higher fuel flow rate. In the natural flickering regime, the dominating frequency of flame flickering remains within a small range, 12.5 Hz to 15 Hz, for all the burners and for all fuel flow rates. The timeaveraged flame length-scale parameters, such as the maximum and the minimum flame heights, increase with respect to the fuel flow rate, however, the difference in the maximum and the minimum flame heights remains almost constant.

Effect of sub‐atmospheric pressures on buoyancy‐dominated hydrocarbon fuel fires: An experimental analysis on thermal flickering frequency

“…Stainless steel fuel tube of the burner has an inner diameter of 5.0 mm with a tapered exit to reduce the formation of turbulent eddies. Selection of this burner diameter was to create a broad range (three orders of magnitude) of number and was similar to previous studies 27,28 . Besides, the flickering frequency of buoyant diffusion flames was found to be independent of the nozzle diameter 2 .…”

“…The perturbation of the surrounding flow field inside the chamber is the potential causes of intermittent flickering. As it was pointed out by Manikantachari et al, 28 the flame is sensitive to certain flow field disturbances in the intermittent flickering state. These disturbances cause the flame to flicker for some time intervals.…”

“…Selection of this burner diameter was to create a broad range (three orders of magnitude) of Fr number and was similar to previous studies. 27,28 Besides, the flickering frequency of buoyant diffusion flames was found to be independent of the nozzle diameter. 2 Sintered metal foam elements placed in the fuel nozzle minimize the instabilities in the initial fuel flow and create a top-hat velocity profile on the exit.…”

Similarity of dynamic behavior of buoyant single and twin jet-flame(s)

“…Thus, this type of dynamic behavior of the flame is often described as the "varicose mode" of the oscillation (Hamins et al, 1992;Cetegen and Ahmed, 1993;Meyer et al, 1999;Takahashi et al, 2007;Hu et al, 2015). Additionally, the flame occasionally exhibits another type of periodic motion of the sinuous meandering fashion as reported in previous studies (Cetegen and Dong, 2000;Manikantachari et al, 2015). Once this dynamics mode appears, the mushroom shape is no longer formed and the detachment of the cap becomes less pronounced.…”

Vortex-dynamical interpretation of anti-phase and in-phase flickering of dual buoyant diffusion flames

“…Probably due to its intrinsic unsteadiness, this problem has not been sufficiently understood, even for the simplest scenario-the interaction of two flames [5][6][7][8][9]. In fact, the unsteadiness could originate from a single flame, for example the "flickering" or "puffing" of a buoyant diffusion flame [10][11][12][13][14][15][16][17][18][19][20][21]. Flickering is a periodic flame oscillation phenomenon.…”