Studies On The Combustion Characteristics Of Liquid Fuel In Capillary Tube

With the wide use of mobile electronic devices, power systems with high-energy density, small volume and light weight equipment are in great demand. New type of liquid hydrocarbon fuel has high energy density, it is necessary to study on the basis of micro scale combustion power generation system. In order to understand diffusion flame characteristics of liquid fuels in a micro-tube, four types of liquid fuels are chosen, i.e.Iso-octane, ethanol, n-heptane and kerosene. Experimental and numerical studies were conducted in a micro-tube with inner diameter of 0.3mm and outer diameter of 0.5mm. In the experiments, micro tubes made of quartz and stainless steel are used, and their effects on flame are obtained. Effects of fuel types, fuel flow rate, material of tube and the tube placement on laminar flame are also investigated. It is found that high wall conductivity is advantageous for liquid fuel evaporation, and the micro-flame is longer in the stainless steel tube. Furthermore, fuel flow rates have great effects on flame length and wall temperature.With fuel flow rate increasing, the flame length first increases and then does not change. At a large flow rate, liquid fuel cannot be completely evaporated and small droplets are ejected with fuel vapor from the tube, resulting in a long plume flame. Due to the effects of buoyancy, flame length of the horizontal jet is much shorter than the length predicted by the empirical equation. Furthermore, fuel types have great effects on flame stability and flame length. Flammable limits of ethanol are much narrow due to a relative lower combustion heat. But kerosene flame is the brightest in four fuels due to high C/H. Additionally, it is found that when the flame is stable, the interface of liquid and gas does not move significantly, but there is a minor oscillation of the fuel film. Additionally, the wall temperature of QT is higher than that of SST, All of these is attributed to that thermal conductivity of SST is 15W/(m · K), 12.3 times larger than that of QT. The thermal conductivity is greater, more heat are exchange between tube and outside world, the tube wall temperature is lower. Studies have shown that at low flow rate, capillary placement of fuel burner has little effect on flame characteristics; when Qf is 70μl/min, compared tohorizontal burner flame L/D increases in vertical burner,which reaches 43.5. But the wall highest temperature is 386, which reduced nearly 250 K.Finally, using two dimensional adaptive grid and one-step chemical reaction model,we research the flame characteristics at different flow rate. Numerical results show that flame characteristics of the simulation is in agreement with the experimental data. This also proves the reliability of the established physical model.