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고일민(Il Min Ko),서정일(Jeong Il Seo),홍정구(Jung Goo Hong),신현동(Hyun Dong Shin) 한국연소학회 2006 KOSCOSYMPOSIUM논문집 Vol.- No.-
A characterization of turbulent reacting flows has proved difficult owing to the complex interaction between turbulence, mixing, and combustion chemistry. There are many types of time scales in turbulent flame which can determine flame structure. This counter jet type premixed burner produces high intensity turbulence. The goal is to gain better insights into the flame structures at high turbulence. 6 propane/air flames gave been studied with high velocity fluctuation in bundle type nozzle and in one hole type nozzle. By measuring velocity fluctuation, turbulent intensity and integral length scale are obtained. And sets of OH LIF images were processed to see flame structure of the mean flame curvatures and flame lengths for comparison with turbulence intensity and turbulent length scales. The results show that the decrease in nozzle size generates smaller flow eddy and mean curvatures of the flame fronts, and a decrease in Damkohler number estimated from flow time scale measurement.
연료 희석이 단면확대 채널에 형성된 삼지화염의 전파속도에 미치는 영향에 관한 실험적 연구
서정일(Jeong Il Seo),신현동(Hyun Dong shin),김남일(Nam Il Kim) 한국연소학회 2007 KOSCOSYMPOSIUM논문집 Vol.- No.-
When triple flames propagated in a diverging channel, the effects of fuel dilution on the lift-off characteristics of triple flames were investigated. A multi-slot burner was used to stabilize the lift-off flame especially at weak fuel concentration gradients. It was reported that there is a maximum propagation velocity at a critical concentration gradient in an open jet regardless of fuel dilution. The enhancement of a diffusion flame affected to increase the propagation velocity around critical concentration gradients. However, the influence of a confined channel on the structure of triple flames according to fuel dilution needs to be investigated compared with an open jet case. This study aimed to examine the effect of a confined channel on the structure and the propagation velocity of the triple flames according to fuel dilution. Lift-off height and propagation velocity of triple flames were investigated by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% N₂). Fuel dilution reduced the propagation velocity of triple flame in a confined channel mainly due to the decrease of flame temperature in premixed branch. Despite the difference in fuel dilution, the propagation velocity has a maximum value at a specific fuel concentration gradient even though the critical concentration gradient increases with fuel dilution. And the critical concentration gradient in a confined channel is larger than that in an open jet due to enhancement of convective diffusion.
연료 희석에 따른 삼지화염의 부상특성에 관한 실험적 연구
서정일(Jeong Il Seo),김남일(Nam Il Kim),신현동(Hyun Dong Shin) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The effects of fuel dilution on the lift-off characteristics of triple flames were studied experimentally using a multi-slot burner, which can stabilize the lift-off flame especially at weak fuel concentration gradients. Contribution of diffusion branch to the propagation velocity of triple flame was examined by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% N2). Lift-off height, axial velocity variation, and OH radical are measured by various laser diagnostic methods (ICCD camera, PIV system, OH-LIF etc.). Fuel dilution reduced the propagation velocity of triple flame mainly due to the decrease of flame temperature in premixed branch, and resulted in a significant change in flame stabilization conditions. OH radical in the diffusion branch is not clearly observed behind the premixed branches at very weak fuel concentration gradient, but becomes prominently active at the specific fuel concentration gradient. Despite the difference in fuel dilution, lift-off heights of triple flame have minimum value during the increase of fuel concentration gradient resulting in U-shaped trends. This fact means that the propagation velocity has a maximum value at a specific fuel concentration gradient regardless of the fuel dilution even though the critical concentration gradient varies. The enhancement of the OH radicals near the maximum propagation velocity was more clearly detected in higher dilution case. Thus the effect of the diffusion flame on the propagation velocity of triple flame needs to be reconsidered.
연료 희석이 단면 확대 채널 내에 형성된 삼지화염의 부상특성에 미치는 영향에 관한 실험적 연구
서정일(Jeong Il Seo),김남일(Nam Il Kim),신현동(Hyun Dong Shin) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
When triple flames propagated in a diverging channel, the effects of fuel dilution on the lift-off characteristics of triple flames were investigated. A multi-slot burner was used to stabilize the lift-off flame especially at weak fuel concentration gradients. It was reported that there is a maximum propagation velocity at a critical concentration gradient in an open jet regardless of fuel dilution. The enhancement of a diffusion flame affected to increase the propagation velocity around critical concentration gradients. However, the influence of a confined channel on the structure of triple flames according to fuel dilution needs to be investigated compared with an open jet case. This study aimed to examine the effect of a confined channel on the structure and the propagation velocity of the triple flames according to fuel dilution. Lift-off height and propagation velocity of triple flames were investigated by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% N₂). Fuel dilution reduced the propagation velocity of triple flame in a confined channel mainly due to the decrease of flame temperature in premixed branch. Despite the difference in fuel dilution, the propagation velocity has a maximum value at a specific fuel concentration gradient even though the critical concentration gradient increases with fuel dilution. And the critical concentration gradient in a confined channel is larger than that in an open jet due to enhancement of convective diffusion.