Abstract:A small scale ceramic tube was used as a combustor nozzle, and a coaxial jet ethanol flame was established in the confined space between the ceramic tube and the quartz glass tube. The fuel flow rates were 0 ~ 2.1mL/h, and the ceramic tubes with inner diameters of 1.0mm and 0.6mm. The small jet flame characteristics were analyzed, while some relevant characteristic parameters were discussed. Some important parameters were selected, including high temperature droplet evaporation rate, normalized heat loss, and quenching diameter. Based on these, the effects of the fuel flow rate and the nozzle inner diameter on flame characteristics, including stabilities, flame temperature and flame shape, in the confined space were investigated experimentally and numerically. When the liquid ethanol flow increased from zero, the change process went through five stages and the flame temperature increased. When the burner nozzle diameter was reduced, the flame became smaller. The results showed that fuel flow and nozzle diameter played an important role in fuel evaporation and combustion process. In the stable combustion stage, overall fuel evaporation, flame temperature and height all increase with the increasing of the fuel flow rate, resulting in flame ignition difficulty in low flow rate and flame oscillation in high flow rate. Normalized heat loss increases, flame temperature and height both decrease due to the diminishment of the nozzle diameter and it would affect the flame stability. Properly adjusting the fuel flow rate and the burner nozzle diameter is helpful to enhance the flame stability.
