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메탄/공기 층류 부분예혼합화염의 상세 라디칼(OH*, CH* 그리고 C<sub>2</sub>*) 정보와 배기매출물에 관한 실험적 연구
정용기,오정석,전충환,장영준,Jeong Yong Ki,Oh Jeong Seog,Jeon Chung Hwan,Chang Young June 대한기계학회 2005 大韓機械學會論文集B Vol.29 No.2
An experimental study was performed to investigate the effects of partially premixing, varying the equivalence ratios from $0.79{\sim}{\infty}$, on NOx emissions and chemiluminescence of excited $OH^{\ast},\;CH^{ast}\;C_2^{\ast}$ radicals in laminar partially premixed flames. the signal from the electronically excited state of $OH^{\ast},\;CH^{ast}\;C_2^{\ast}$ was detected through a band pass filter with a photo multiplier tube, which are processed to the intensity ratio ($C_2^{\ast}/CH^{\ast},\;C_2^{\ast}/OH^{\ast},\;and\;CH^{\ast}/OH^{\ast}$) to reveal the correlation with local equivalence ratio. And measurements of NOx emission were made to investigate the relationship between visible flame appearance, chemiluminescence, and EINOX. The results demonstrated that (1) the flames at ${\phi}<1.59$ exhibited classical double flame structure, at ${\phi}>4.76$, the flames exhibited diffusion flame structure, and the intermediate flames at $1.59<{\phi}<4.76$ was a merged flame, (2) the $OH^{\ast}$ peak was located inside the $CH^{\ast}\;and\;C_2^{\ast}$ radical for all measured conditions and the emission intensity ratio of $C_2^{\ast}/CH^{\ast}\;and\;C_2^{\ast}/OH^{\ast}$ were identified as good marker for local equivalence ratio over a range of ${\phi}=0.79{\sim}1.2\;and\;CH^{\ast}/OH^{\ast}\;is\;0.79<{\phi}<1.9$. However, it was difficult to predict the equivalence ratio in partially premixed flames using this system for ${\phi}>2.38$, (3) the minimum NOX emission index (EINOx) is obtained for a equivalence ratio of 3.19 in the intermediate flames.
이중동축 메탄/공기 층류 부분 예혼합화염에서의 화염구조와 자발광 배출 특성 안쪽관 연료주입의 영향
오정석(Jeong Seog Oh),정용기(Yong Ki Jeong),전충환(Chung Hwan Jeon),장영준(Young June Chang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
In this study, the effect of central fuel injection on a coaxial laminar CH₄/air flame was experimented at the defined premixing condition(φ=1.90, σ=50/75/100%, x/D=10). The partial premixing parameter are the equivalence ratio that total fuel is fixed at 200cc/min, the fuel split degree which means the percentage of fuel entering the outer tube to the total amount, and the mixing distance indicating the nonreactant mixture's homogeneity between inner tube top and burner exit. The object is to investigate the flame structure and chemiluminescence characteristics of laminar partial premixed flame as changing mixing parameters. The radical signal was acquired from ICCD camera and PMT. Each intensity was compared with Abel inverted value for measuring the effect of background light on the peak signal location and the intensity at central preheat zone. The results show that the peak location of each radical was broaden as the fuel split degree increasing because the mixing quality was enhanced. and OH* is a good indicator for flame front between reaction and preheat zone. At last C₂* has the same tendency with CH* but a thinner reaction zone than CH* due to a rapid decay on the burned gas side.
메탄 공기 층류 부분 예혼합화염에서 예혼합 정도에 따른 화염구조와 질소산화물의 배출에 미치는 영향에 관한 연구
오정석(Jeong Seog Oh),정용기(Yong Ki Jeong),전층환(Chung Hwan Jeon),장영준(Young June Chang) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
It is shown that the effect of variable parameters on flame structures and NOx emissions in the laminar<br/> partially premixed methane-air flames with a co-axial Bunsen burner. Objectives of this paper is to<br/> understand the effects of flow variables on NOx emissions and the flame structure with OH<br/> chemiluminescence, including reconstructed image by abel inversion processing at each conditions. A fuel<br/> flowrate of 200 [cc/min] was fixed and the amount of air was varied from 400 to 1200 [cc/min]. The<br/> experimental variables were equivalence ratio( ), fuel split percentage( ) and inner tube recess(x/D). Flow<br/> conditions were ranged from 1.36~4.76(equivalence ratio), 50~100(fuel split percentage) and 0~20(inner<br/> tube recess). NOx analyzer and ICCD camera with a OH filter were used as a main experimental<br/> apparatus. In addition, Abel inversion, which is a kind of tomography and valuable to estimate a<br/> two-dimensional structure of co-axial flames from cubical information, was employed for combustion<br/> diagnostics. Results from this study indicate that the main effects depend on equivalence ratio and next<br/> sigma, x/D for NOx production and OH formation. Throughout Abel inversion, we could affirm the<br/> maximum position and the tendency of OH radical intensity by variants at five axial heights above the<br/> burner exit.
오충석,이석규 金烏工科大學校 2000 論文集 Vol.21 No.-
We constructed a systematic durability analysis procedure in the automotive industry. By using the procedure, we performed an analysis for the lower control arm. We made a FE model and then evaluated the accuracy of the model through comparisons with actual strain measurements and constant amplitude fatigue tests. The cyclic material properties were obtained from low cycle fatigue tests with ASTM standard specimens. The shear strain distribution of the FE model was similar to that of the photo stress analysis in the longitudinal loading direction. The model predicted von Mises stresses measured from actual strain-gage measurements within 5% error. The fatigue life of the model agreed well with the bench test results within a factor of two. The signed bon Mises method showed the better fatigue life prediction than the absolute maximum principal or the signed Tresca method did. The proposed procedure proved to be very reliable quantitatively as well as qualitatively.
Fatigue Properties of Copper Foil and the Evolution of Surface Roughness
Chung-Seog Oh,Jong-Sung Bae,Hak-Joo Lee 한국정밀공학회 2008 International Journal of Precision Engineering and Vol.9 No.4
The aim of this investigation was to extract the fatigue properties at the designated fatigue life of copper foil and observe the mean stress and stress amplitude effects on both the fatigue life and the corresponding surface morphology Tensile tests were performed to determine the baseline monotonic material properties of the proportional limit and ultimate tensile strength. Constant amplitude fatigue tests were carried out using a feedback-controlled fatigue testing machine. The mean stress and the stress amplitude were changed to obtain the complete nominal stress¬life curves. An atomic force microscope was utilized to observe the relationship between the fatigue damage and the corresponding changes in surface morphology. A Basquin's exponent of-0.071 was obtained through the fatigue tests. An endurance limit of 122 MPa was inferred from a Haigh diagram. The specimen surface became rougher as the number of fatigue cycles increased, and there was a close relationship between the fatigue damage and the surface roughness evolution.
Fatigue Crack Growth Behavior of Corner Cracks under LBH Loading
Oh, Chung Seog,Park, Philip,Huh, Yong Hak,Ko, Soon Gyu,Hwang, Don Young,An, Hyeon Mo Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-
<P>This investigation aims at doing some durability and damage tolerant (DaDT) tests with 2124-T851 aluminum specimens having corner cracks under a random history, correlating with the simulation results from AFGROW and then drawing some conclusions from those comparisons. Two hydraulic actuators and a homemade Wood’s alloy grip are employed to do the test. The surface crack lengths are measured by a traveling microscope and used as a reference for the later fractography. The crack penetration and the total lives are about 17 and 27 blocks, respectively. The crack length and depth are evaluated by the fractography after completing each test and used to grasp the shape change. The Forman equation is used to simulate the fatigue crack growth behavior according to a bearing stress ratio extensively. The crack penetration life is decreased as the bearing stress ratio increases. The crack aspect ratio is very dependent on the bearing stress ratio. The LBH loading accelerates the fatigue crack growth in the crack depth direction but decelerates that in the length direction until crack penetration.</P>
Fatigue Properties of Copper Foil and the Evolution of Surface Roughness
Oh, Chung-Seog,Bae, Jong-Sung,Lee, Hak-Joo Korean Society for Precision Engineering 2008 International Journal of Precision Engineering and Vol.9 No.4
The aim of this investigation was to extract the fatigue properties at the designated fatigue life of copper foil and observe the mean stress and stress amplitude effects on both the fatigue life and the corresponding surface morphology. Tensile tests were performed to determine the baseline monotonic material properties of the proportional limit and ultimate tensile strength. Constant amplitude fatigue tests were carried out using a feedback-controlled fatigue testing machine. The mean stress and the stress amplitude were changed to obtain the complete nominal stress-life curves. An atomic force microscope was utilized to observe the relationship between the fatigue damage and the corresponding changes in surface morphology. A Basquin's exponent of-0.071 was obtained through the fatigue tests. An endurance limit of 122 MPa was inferred from a Haigh diagram. The specimen surface became rougher as the number of fatigue cycles increased, and there was a close relationship between the fatigue damage and the surface roughness evolution.
오충석(Chung-Seog Oh),송지호(Ji-Ho Song) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
Fatigue crack growth and closure behaviour of surface cracks as well as through-thickness cracks in aluminium alloy 7075-T65l are investigated under pure bending loading. We have placed a special focus on the comparison of the surface crack closure behaviour under two loading cases, axial and bending, and also with the through-thickness cracks. The ratio of crack opening ratio in the crack length direction to that in the crack depth direction is close to 0.9 regardless of the applied loading types and the stress ratios. Growth rates of surface cracks can be successfully explained in terms of the effective stress intensity factor range, independently of the loading type, the crack shape and the stress ratio.