메탄/순산소 혼합층에서 Edge Flame의 구조

최상규(S. K. Choi),김준홍(J. Kim),정석호(S. H. Chung),김종수(J. S. Kim) 한국연소학회 2006 한국연소학회지 Vol.11 No.1

Structure of edge flame established in a mixing layer, formed between two uniformly flowing pure CH₄ and pure O₂ streams, is numerically investigated by employing a detailed methane-oxidation mechanism. The numerical results exhibited the most outstanding distinction of using pure oxygen in the fuel-rich premixed-flame front, through which the carbon-containing compound is found to leak mainly in the form of CO instead of HC compounds, contrary to the rich CH4-air premixed flames in which CH₄ as well as C₂Hm leakage can occur. Moreover, while passing through the rich premixed flame, a major route for CO production, in addition to the direct CH₄ decomposition, is found to be C₂Hm compound formation followed by their decomposition into CO. Beyond the rich premixed flame front, CO is further oxidized into CO₂ in a broad diffusion-flame-like reaction zone located around moderately fuel-rich side of the stoichiometric mixture by the OH radical from the fuel-lean premixed-flame front. Since the secondary CO production through C₂Hm decomposition has a relatively strong reaction intensity, an additional heat-release branch appears and the resulting heat-release profile can no longer be seen as a tribrachial structure.

소형 정밀 왕복동기기용 선형 탄성 베어링 모델(KIMM-LFB)의 설계 및 해석

최상규(S.-K. Choi),박성제(S. J. Park),홍용주(Y. J. Hong),김효봉(H. B. Kim) 한국소음진동공학회 2002 한국소음진동공학회 학술대회논문집 Vol.2002 No.11

합성 가스의 희박 연소에서 NO 발생특성에 관한 수치해석

최상규(S. K. Choi),정석호(S. H. Chung) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

NO emission characteristics of syngas combustion at various reforming ratios were studied numerically. The syngas was formed by the partial oxidation of methane to mainly hydrogen and carbon monoxide. Lean premixed flames in a counterflow were calculated for the cases of atmospheric temperature and adiabatic condition during the mixing process with methane fuel. Flame structure, extinction characteristics, and nitric oxide formation were studied for various reforming ratios and stretch rates. The maximum flame temperature increased with the reforming ratio for both temperature cases, except for the region of very low stretch rate of atmospheric condition. For a specified reforming ratio, the maximum flame temperature increased and then decreased as stretch rate increases. This trend was more remarkable at higher reforming ratios, which is attributed to the preferential diffusion effect of hydrogen in syngas. EINO increased with the reforming ratio for both temperature cases. The increasing and decreasing trend of EINO with stretch rate is similar to that of the maximum flame temperature. NO emission was mostly by prompt mechanism, because the flame temperature is relatively low. Prompt NO by HNO, NNH, NH was increased with reforming ratio.

소형 정밀 왕복동기기용 선형 탄성 베어링 모델(KIMM-LFB)의 설계 및 해석

최상규(S.-K. Choi),박성제(S. J. Park),홍용주(Y. J. Hong),김효봉(H. B. Kim) 한국소음진동공학회 2002 한국소음진동공학회 심포지엄 Vol.2002 No.1

합성 가스의 비예혼합 화염에서 NO 발생특성에 관한 수치해석

최상규(S. K. Choi),정석호(S. H. Chung) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Characteristics of non-premixed syngas combustion were studied numerically. The syngas was mainly composed of hydrogen and carbon monoxide, formed by partial oxidation of methane with air. Flame structure, maximum flame temperature, extinction characteristics, and nitric oxide formation were investigated for various reforming ratios and stretch rates in one-dimensional counterflow configuration. The case of high pressure of 10 atm was also studied and compared with the atmospheric pressure. For the case of 10 atm, the maximum flame temperature is higher and its variation with XR is smaller than those at 1 atm. The extinction stretch rate is larger at 10 atm, and increases with XR for both pressure cases. As the stretch rate increases, EINO decreases more abruptly in smaller XR. When XR ? 0.4, EINO increases with XR at the same stretch rate. But in larger XR, EINO decreases as XR increases in the region of relatively lower stretch rate and increases with XR at higher stretch rate. At a specified XR, EINO is lager at 10 atm compared with that at 1 atm except for the region of very low stretch rate. Prompt NO shows negative value at lower XR, but turns to be positive with increasing stretch rate. This trend is more remarkable at 10 atm.

메탄/순산소 혼합층에서 edge flame의 구조

최상규(S. K. Choi),김준홍(J. Kim),정석호(S. H. Chung),김종수(J. S. Kim) 한국연소학회 2006 KOSCOSYMPOSIUM논문집 Vol.- No.-

Structure of edge flame established in a mixing layer, formed between two uniformly flowing pure CH₄ and pure O₂ streams, is numerically investigated by employing a detailed methane-oxidation mechanism. The numerical results exhibited the most outstanding distinction of using pure oxygen in the fuel-rich premixed-flame front, through which the carbon-containing compound is found to leak mainly in the form of CO instead of HC compounds, contrary to the rich CH₄-air premixed flames in which CH₄ as well as C₂Hm leakage can occur. Moreover, while passing through the rich premixed flame, a major route for CO production, in addition to the direct CH₄ decomposition, is found to be C₂Hm compound formation followed by their decomposition into CO. Beyond the rich premixed flame front, CO is further oxidized into CO₂ in a broad diffusion-flame-like reaction zone located around moderately fuel-rich side of the stoichiometric mixture by the OH radical from the fuel-lean premixed-flame front. Since the secondary CO production through C₂Hm decomposition has a relatively strong reaction intensity, an additional heat-release branch appears and the resulting heat-release profile can no longer be seen as a tribrachial structure.

연료 성층화된 채널에서 화염전파 특성에 관한 수치해석적 연구

최상규(S. K. Choi),최병철(B. C. Choi),김준홍(J. Kim),정석호(S. H. Chung) 한국자동차공학회 2009 한국자동차공학회 부문종합 학술대회 Vol.2009 No.4

Characteristics of flame propagation in a 2-D mixing layer of a confined channel are studied numerically. Methane fuel and air as an oxidizer are stratified in linear profiles in channels of different widths, and the flame propagation speed, flame shape and curvature for various initial mass fraction gradients of fuel and channel widths were investigated. Reduced reaction mechanism was adopted for methane oxidation. The flame shape and overall propagation speed is quite different in each channel even at the same mixture fraction gradient. For the channel wieth of 0.25㎝, the flame is tilted to the lean side and the propagation speed increases and then decreases with increasing fuel mass fraction gradient. In wider channels, near-stoichiometric premixed flame is leading, and the flame propagation speed increases with the fuel mass fraction gradient. The reason for the different trend of propagation speed is attributed to the variation of flow characteristics in different channel widths.

합성 가스 연소에서 NO 발생특성에 관한 수치해석적 연구

최상규(S. K. Choi),김민국(M. K. Kim),정석호(S. H. Chung),송영훈(Y. H. Song) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

NO emission characteristics of syngas combustion were studied numerically for various reforming rates, XR Symmetrical double premixed flames were calculated using one-dimensional code for the cases of atmospheric temperature and high-temperature syngas formed through partially oxidizing of methane, and compared with high-pressure cases. When syngas of 298K was used, for both 1 atm and 10 atm cases, EINO was decreased as XR increases at low stretch rates, but increased as XR at high stretch rates near extinction. When high-temperature syngas was used, for 1 atm case, EINO was increased with increasing XR through the whole range of stretch rates. For 10 atm case, BINO shows complicated trend with XR at each range of stretch rate. Although the flame temperature rises with XR when using high-temperature syngas, thermal NO was decreased. The reason is thought that the production of N radical by CH is weakened because hydrocarbon species are decreased as XR increases, and as a result thermal NO through N radical is decreased.

합성 가스의 연소 특성에 대한 수치적 연구

최상규(S. K. Choi),원상희(S. H. Won),정석호(S. H. Chung),차민석(M. S. Cha),송영훈(Y. H. Song) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Characteristics of syngas combustion was studied numerically for various mixing ratios of methane and syngas which was produced by partial oxidization of methane. Ideal case in which CH₄ is completely decomposed into CO and H₂, and the syngas obtained by equilibrium code which contains other species, were compared. For ideal case, the composition of premixture varies almost linearly for reforming rate, while the composition of syngas from equilibrium code varies nonlinearly and does not vary much until the reforming rate of 0.4. When the mixture of ambient temperature was used, as reforming rate increases, flame temperature decreases but laminar burning velocity increases. This inverse trend which is not general is due to the decrease of overall activation energy as reforming rate. The exponential term of the reaction rate which contains the activation energy and temperature shows similar trend to the laminar burning velocity. Lean flammability limit is expanded, and extinction stretch rate of diffusion flame is increased as reforming rate increases. The flame characteristics is more improved for the ideal case, it will be important to reform effectively to achieve better performance of combustor.

Synthesis of vertically aligned thin multi-walled carbon nanotubes on silicon substrates using catalytic chemical vapor deposition and their field emission properties

S. I. Jung(정승일),S. K. Choi(최상규),S. B. Lee(이승백) 한국진공학회(ASCT) 2008 Applied Science and Convergence Technology Vol.17 No.4

최적화된 량의 황화수소 첨가 가스를 이용하여 실리콘 기판위에 증착된 Fe/Al 박막위에 촉매 화학 기상 증착법을 사용하여 직경이 얇은 다중층 탄소나노튜브가 수직 정렬되어 합성되었다. 주사전자현미경 관측 이미지에서 합성된 탄소나노튜브는 상대적으로 일정한 길이를 가지고 기판에 수직으로 정렬되었다. 투과전자현미경 관측에서 합성된 탄소나노튜브는 10㎚ 이내의 작은 외경을 가졌고 촉매가 거의 없었다. 평균 튜브의 벽 수는 약 다섯 개이다. 수직 정렬된 직경이 얇은 다중층 탄소나노튜브의 성장 메카니즘이 제시되었다. 수직 정렬된 직경이 얇은 다중층 탄소나노튜브는 0.1 ㎂/㎠의 전류밀도에서 약 1.1 V/㎛ 낮은 턴-옹 전계를 나타내었고 2.7 V/㎛의 전계에서 약 2.5 ㎃/㎠의 전류밀도를 얻었다. 게다가, 수직 정렬된 직경이 얇은 다중층 탄소나노튜브는 약 1 ㎃/㎠의 전류밀도에서 20시간동안 전류밀도 저하 없이 좋은 전계 방출 안정성을 보여주었다. We have succeeded in synthesizing vertically aligned thin multi-walled carbon nanotubes (VA thin-MWCNTs) by a catalytic chemical vapor deposition (CCVD) method onto Fe/Al thin film deposited on a Si wafers using an optimum amount of hydrogen sulfide (H₂S) additive. Scanning electron microscope (SEM) images revealed that the as-synthesized CNT arrays were vertically well-oriented perpendicular to the substrate with relatively uniform length. Transmission electron microscope (TEM) observations indicated that the as-grown CNTs were nearly catalyst-free thin-MWCNTs with small outer diameters of less than 10㎚. The average wall number is about 5. We suggested a possible growth mechanism of the VA thin-MWCNT arrays. The VA thin-MWCNTs showed a low tum-on electric field of about 1.1 V/㎛ at a current density of 0.1 ㎂/㎠ and a high emission current density about 2.5 ㎃/㎠ at a bias field of 2.7 V/㎛. Moreover, the VA thin-MWCNTs presented better field emission stability without degradation over 20 hours (h) at the emission current density of about 1 ㎃/㎠.