Characteristics of Small Diffusion Flames in a Confined Space

Abstract

With the demand of smaller scale and higher energy density power sources, Micro Energy System has received more and more concern in last few years. Flame shape is an important characteristic of laminar diffusion flames. Experiments were performed to investigate the small diffusion flames burning, liquid ethanol in quiescent, room-temperature air. Ethanol diffusion flames were stabilized on top of vertical capillary tubes. Test conditions involved burner inner diameters of 1.0 mm, and fuel mass flowrates of 1.8–2.25 ml/h. The laminar diffusion flame in a confined physical environment is considered with fuel (ethanol) admitted as a central jet and air as a co-flowing annular jet. The burner outer diameter is 2mm, and inner diameter of the tube outside the burner is 8.8mm. The extremely small ethanol flowrates were accurately controlled by a syringe pump. The flame shapes were visually observed using a high speed CCD camera. Normalized lengths of flames were correlated with Reynolds number, and Normalized widths of flames were correlated with Reynolds number and Froude number respectively. The experimental results were compared with classical theory for diffusion flames.