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미소중력 환경내의 벽면 근방 확산 화염 특성에 관한 수치 해석
최재혁,후지타 오사무,Choi Jae-Hyuk,Fujita Osamu 한국마린엔지니어링학회 2006 한국마린엔지니어링학회지 Vol.30 No.1
Characteristics of a laminar diffusion flame placed near wall in microgravity have been numerically analyzed in a two-dimension. The fuel for the flame is $C_2H_4$. The flame is initiated by imposing a high temperature ignition source. The flow field, temperature field, and flame shape in microgravity diffusion flame are detailed. Especially, effects of surrounding air velocity and fuel injection velocity on the microgravity diffusion flame have been discussed accounting for standoff distance. And, the effect of curvature rate has been also studied. The results showed that velocities in a diffusion flame were overshoot because of volumetric expansion and distribution of temperature showed regularity by free-buoyancy This means that the diffusion flame in microgravity is very stable, while the flame in normal gravity is not regular and unstable due to buoyancy. Standoff distance decreases with increase in surrounding air velocity and with decrease in fuel injection velocity. With increasing curvature rate, the position of reaction rate moves away the wall.
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미소중력환경을 이용한 벽면근방 확산화염내 매연부착거동의 원위치 관찰
최재혁,후지타 오사무,Choi Jac-Hyuk,Fujita Osamu 한국마린엔지니어링학회 2005 한국마린엔지니어링학회지 Vol.29 No.8
Experiments at the Japan Microgravity Center (JAMIC) have investigated the interaction between diffusion flames and solid surfaces Placed neat flames The fuel for the flames was $C_{2} H_{4}$ The surrounding oxygen concentration was 35$\%$ with surrounding air temperatures of $T_{a}$ : 300K. Especially, the effect of wall temperature on soot deposition from a diffusion flame Placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures. $T_{w}$=300, 800 K, were selected as test conditions The results showed that the soot distribution between flame and burner wall was strong1y affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values lot two different wall temperatures suggests that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.
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미소중력환경에서의 고체벽면근방 층류확산염내 매연입자의 열영동 부착
최재혁(Jae-Kyuk Choi),후지타 오사무(Fujita Osamu),정석호(Suk-Ho Chung) 한국연소학회 2007 KOSCOSYMPOSIUM논문집 Vol.- No.-
The deposition behavior of soot particles in a diffusion flame along a solid wall was examined experimentally by getting rid of the effect of natural convection utilizing micro gravity environment. The microgravity environment was realized by using a drop tower facility. The fuel for the flame was an ethylene (C₂H₄) and the surrounding oxygen concentration 35% with the surrounding air velocity of Va=2.5, 5, and 10 ㎝/s. Laser extinction method was adopted to measure the soot volume fraction distribution between the flame and burner wall. The results show that observation of soot deposition in normal flame was difficult from buoyancy and the relative position of flame and solid surface changes with time. The soot particle distribution region moves closer to the surface of the wall as the surrounding air velocity is increased. And the experiments determined the trace of the maximum soot concentration line. It was found that the distance between soot line and flame line is around 5 ㎜. That is, the soot particle near the flame zone tends to move away from flame zone because of thermophoretic force and to concentrate at a certain narrow area inside of the flame, finally, to adhere the solid wall.
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