甲烷射流扩散火焰结构试验研究

Experimental study of flame shape of methane jet diffusion flame

利用不同口径、不同流量的甲烷射流扩散火试验研究了射流扩散火焰结构特征,得到了射流火从层流燃烧到湍流燃烧再到吹熄的一般规律。结果表明,不同口径射流火在层流扩散燃烧与湍流扩散燃烧时火焰高度的变化各有不同。火焰最大高度出现在湍流扩散燃烧阶段。某些工况下燃烧出现脉动火焰现象,此时的火焰高度较小。

An experiment has been carried out to study on flame shape of methane jet diffusion flame. 6 different diameter nozzles, which.minimum and maximum diameters were 3 mm and 25 mm respectively, have been used in the experiment, and the flow rate under the standard state of jet diffusion flame were from 32 L/h to 7 098 L/h. The flame height was calculated by image processing software. The flame height has taken the value of intermission rate I = 0.5. The process which from laminar diffusion to fully developed turbulent diffusion had been described in detail, including its change of flame color and height. Also the fluctuation flame has been described. The general rule of shape change of jet diffusion flame has been given. 3 mm, 4 mm and 5 mm diameter nozzles＇ jet flame had appeared blowing off, and the blowing-off flow rate were about 1 500 L/h, 3 600 L/h and 6 000 L/h respectively. It was been found that laminar jet diffusion flame height increased faster than turbulent jet diffusion flame height. The maximum height had appeared at fully developed turbulent diffusion stage, and flame height almost had no change by increasing methane flow rate after flame gets the maximum height. The maximum jet flame height of each nozzle had seemed to be linear proportional to the methane flow rate. Flame height of small diameter nozzles had decreased slightly at the stage between laminar diffusion and turbulent diffusion, and turbulent diffusion flame has seemed to appear on the top of laminar jet diffusion flame. The reason was because of that turbulent diffusion made the combustion faster, which made methane, had already burned before reaching the height of laminar diffusion flame. Fluctuation flame, with frequency were between 4- 6 Hz, has appeared at bigger diameter nozzles at low flow rate, which had smaller flame height than other jet flame that had same flow rate and different diameters.