Experiment And Numerical Simulation On Structure Features Of Diffusion Flames In Moving Fire

Air turbulent caused by moving fire source combustion is under the double influence ofboth fire source movement and combustion. As a result, the flame structure will become morecomplex. By reference to literatures and documents recently available, the immanent physicalnature and disciplinarian of diffusion flame structure caused by moving fire source have beenstill failed to clear understanding, and also have no representation of its flamelet structuremode. Taking diffusion flame caused by moving fire source combustion as the investigationsubject, this paper mainly focus on diffusion flame structure, such as static characteristic,dynamic characteristic and combustion stability. This implementation of the project will helpto broaden the knowledge of diffusion flame theory, and will have made positivecontributions to the enrichment and development of diffusion flame theory of moving firesource.Under the permission of experiment outlay, a fire wind tunnel experimental device forlinear motion and rotating experimental device for rotation movement are designed and set upby the author. The cross section of the wind tunnel is0.3m×0.3m, and its length is3.6m. Thewind speed in the fire wind tunnel can be adjusted between0~5m/s. Using this device, aseries of static and motion experimental pictures in different speeds are taken by digitalcamera system. The radius of rotating experimental device is0.5m. The rotation rate, which iscontrolled by frequency-conversion speed governor, can be adjusted between0~50Hz. Usingthis device, a series of diffusion flame pictures in various rotation rates are gathered by highspeed camera. The above experiments systematically provided important laboratory data fordiffusion flames research.It is a mature technology to process images with nonlinear method. The diffusion flamepictures of linear motion and rotational movement are processed under MATLAB to get staticand dynamic characteristics of diffusion flames. These pictures help us to analyze exteriorcharacteristics, combustion height and the change of edge and area of diffusion combustionflame.In recent years, many scholars at home and abroad have studied flame structures byusing computational fluid dynamics, but the flame structures they studied are almost causedby static fire combustion and not involved flame structures caused by moving fire. So, thispaper adopted two-dimension dynamic simulations to simulate linear motion under FLUENT6.3. By simulating linear motion, the distributing laws and characteristics of temperature field, pressure field and velocity field of the diffusion combustion are given in different speeds. Theresults showed that it is significant different between relative rest and absolute rest aboutcombustion. Such as the relative rest combustion is more turbulent, more contact between airand fuel than absolute rest. And maximum temperature of the former is higher than the latter.Therefore, it is not exactly same between relative rest and absolute rest about combustion ofmoving fire, such as the flame shape and temperature distribution varies widely in externalwind speed and fire moving by itself.We also studied diffusion flame structures and combustion regulations of moving fire inrotating motion by using FLUENT6.3. By simulation we get contours of temperature,contours of velocity and the process of flameout. We found that as rotate speed increases, theresistance of the air on diffusion flame increases and deflection angle increases. At the sametime rotate speed increases, the air turbulence around diffusion flame increases, much moreair contact and react with fuel, and Air Fuel Ratio (AFR) increases. This process of increasingrotate speed benefits combustion.The mechanism of extinction in diffusion combustion of moving fire is that when rotate speedcontinue increasing, the air turbulence speeds up heat dissipation to weaken combustion. Atthe same time, air flow takes away fuel heat of reaction to shrink the flame until flameout. Onthe other hand, when the external pressure is greater the fuel injection pressure, the fuel wasprevented with the outside air, the flame is off.