Experimental And Numerical Investigation On The Characteristics Of The Small-scale Jet Diffusion Flame

Micro Electronic Mechanical System which is based on the fuel combustion has the characteristics of high energy density. The requirement for such systems is increasing. Over the past decade, researches in this area are becoming hot at homeland and abroad. Developments of micro energy systems which are small size, light weight, high energy density and it can be sustained for energy have important significance. Compared with the large-scale combustor, the micro combustor, which is the core of the micro energy system, has some different characteristics, such as the ratio of surface area to volume is relatively large, heat loss increasing, short residence time, and so on. The effect of factors on micro flame stability and other characteristics are the focus of attention of domestic and foreign researchers.Compared with gaseous fuel, liquid fuel combustion process is more complicated. But it has a higher energy density, and it is more suitable for micro combustor. In this paper, liquid ethanol is used as fuel, and experimental study and numerical simulation are both used to analyze the effects of factors on the small-scale ethanol diffusion flame characteristics which include flame shape, temperature, combustion stability, and so on. The factors include burner nozzle diameter, fuel flow, applied DC field and so on. And the combustion mechanism of micro-scale flame of liquid fuel is discussed.In the numerical simulation, Fluent 6.3 is used to build a two-dimensional numerical symmetry combustion model. The simulation results are in good agreement with the experimental results, and the accuracy of numerical simulation results in this paper is verified.The results show that, 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. In the stable combustion stage, overall fuel evaporation, flame temperature and height all increase with the increasing of the fuel flow rate, and that normalized heat loss increases, flame temperature and height both decrease due to the diminishment of the nozzle diameter. The flame heat loss is reduced by the external electrical heating. The external electrical heating raises the flame temperature. And the chemical reaction rate becomes faster, and the micro-flame shifts upstream. And in the DC electric field, the small flame size becomes smaller, the temperature increases, and the velocity field, component distribution and chemical reaction rate are all changed. Properly adjusting the fuel flow rate and the burner nozzle diameter, external electrical heating or DC electric field is helpful to enhance the flame stability. Changing small flame characteristics by applied electric field with low electric power consumption has application prospect.The change rules of different factors on the ethanol small-scale jet diffusion flame characteristics are discussed. With the help of simulation software, the internal changes of the small flame are analyzed. It provides technical references for optimizing the design of new structures and experimental micro-combustion system.