Experimental Study on the Diffusion Flame from Small Ceramic Tube

Micro energy system has received great attention in the past few years. Flame structure is an important characteristic of laminar diffusion flames from small burner. Experiments were performed to investigate the small diffusion flames using liquid ethanol as fuel in quiescent, room-temperature air. Ethanol diffusion flames were obtained on top of vertical ceramic tubes. Test conditions involved burner inner diameters of 1.0 mm, 0.6 mm and 0.4 mm, and fuel flow rates of 0.7-2.3 ml/h under steady combustion. The thermal conditions can be changed by adjusting the distance from the top of ceramic tube to the top of copper tube. The extremely small ethanol flow rates were accurately controlled by a syringe pump. The flame structures were visually observed using a high speed CCD camera. Based on the experimental results, several conclusions can be drawn. Increasing the distance, h, the heat transferred to the environment increased, which may caused the flame length decrease. Under steady combustion conditions, the normalized flame lengths all nearly increased linearly with increasing the Reynolds numbers. At a certain Reynolds number, the normalized flame widths increased with the decreasing the inner diameters of burners. The steady combustion limits under different conditions were obtained, and found that the limits become narrow as decreasing the inner diameter of the small ceramic burner.