삼지화염의 전파속도에 대한 속도구배의 영향에 관한 실험적 연구

김민국(M. K. Kim),원상희(S. H. Won),정석호(S. H. Chung),O. Fujita 한국연소학회 2005 KOSCOSYMPOSIUM논문집 Vol.- No.-

층류 예혼합 화염 안정화에 미치는 교류 전기장 효과에 관한 실험적 논문

김민국(M. K. Kim),김환호(H. H. Kim),정석호(S. H. Chung) 한국연소학회 2008 KOSCOSYMPOSIUM논문집 Vol.- No.-

The stabilization characteristics of premixed laminar jet flames have been investigated experimentally for stoichiometric methane-air mixture by varying AC electric fields applied to the nozzle with a single-electrode configuration. The detachment velocities either at blowoff or partial-detachment have been measured by varying the applied voltage and frequency of AC. The result showed that the detachment velocity was increased with the applied AC electric fields, such that the flame was attached to the nozzle exit even over the blowoff velocity without having electric fields. There existed four distinct regimes depending on the applied AC voltage and frequency. In the regime of low electric field intensity, the threshold condition of AC electric fields was observed below which the effect of electric fields on the detachment velocity is minimal. In the moderate voltage, the detachment velocity increased linearly with the applied voltage and nonlinearly with the AC frequency. In the high voltage regime, two different regimes depending on the AC frequency were observed. For relatively low frequency, a half frequency of the flame base oscillation as well as the original frequency of applied AC electric fields was induced and the change of detachment velocity was insensitive to the variation of applied voltage. At high frequency regime, the stability of flame was significantly affected by the generation of streamers and the detachment velocity decreased with the applied voltage.

대향류 버너 확산화염에 대한 AC 전기장의 영향

김형국(H. K. Kim),최병철(B. C. Choi),김민국(M. K. Kim),최재혁(J. H. Choi),정석호(S. H. Chung) 한국연소학회 2008 KOSCOSYMPOSIUM논문집 Vol.- No.-

The effect of AC electric field on flame position in counterflow burner has been investigated experimentally by varying the voltage and frequency. The result showed that the flame position maintained the typical flame shape above critical frequency, which was stable regardless of applied voltage amplitude. In contrary, below critical frequency, the flame position was oscillated. The oscillating flames were categorized in two regimes. For high frequency regime from 2 ㎐ to critical value, the flame position was sinusoidally oscillated with increasing amplitude as applied voltage amplitude increases. And for low frequency regime below 2 ㎐, the flame position was complicatedly oscillated with peak phenomenon having rapid variation of the position. In such a case, the low frequency oscillating flames were controlled by interaction between the flame position variation on DC electric field and the chemically response time on AC electric field.

열 화학기상증착법을 이용한 탄화규소 나노선의 합성 및 특성연구

정민욱,김민국,송우석,정대성,최원철,박종윤,Jung, M.W.,Kim, M.K.,Song, W.,Jung, D.S.,Choi, W.C.,Park, C.J. 한국진공학회 2010 Applied Science and Convergence Technology Vol.19 No.4

One-dimensional cubic phase silicon carbide nanowires (${\beta}$-SiC NWs) were efficiently synthesized by thermal chemical vapor deposition (TCVD) with mixtures containing Si powders and nickel chloride hexahydrate $(NiCl_2{\cdot}6H_2O)$ in an alumina boat with a carbon source of methane $(CH_4)$ gas. SEM images are shown that the growth temperature (T) of $1,300^{\circ}C$ is not enough to synthesize the SiC NWs owing to insufficient thermal energy for melting down a Si powder and decomposing the methane gas. However, the SiC NWs could be synthesized at T>$1,300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is T=$1,400^{\circ}C$. The synthesized SiC NWs have the diameter with an average range between 50~150 nm. Raman spectra clearly revealed that the synthesized SiC NWs are forming of a cubic phase (${\beta}$-SiC). Two distinct peaks at 795 and $970 cm^{-1}$ in Raman spectra of the synthesized SiC NWs at T=$1,400^{\circ}C$ represent the TO and LO mode of the bulk ${\beta}$-SiC, respectively. XRD spectra are also supported to the Raman spectra resulting in the strongest (111) peaks at $2{\Theta}=35.7^{\circ}$, which is the (111) plane peak position of 3C-SiC. Moreover, the gas flow rate of 300 sccm for methane is the optimal condition for synthesis of a large amount of ${\beta}$-SiC NW without producing the amorphous carbon structure shown at a high methane flow rate of 800 sccm. TEM images are shown two kinds of the synthesized ${\beta}$-SiC NWs structures. One is shown the defect-free ${\beta}$-SiC NWs with a (111) interplane distance of 0.25 nm, and the other is the stacking-faulted ${\beta}$-SiC NWs. Also, TEM images exhibited that two distinct SiC NWs are uniformly covered with $SiO_2$ layer with a thickness of less 2 nm. 본 연구에서는 열 화학기상증착법(thermal chemical vapor deposition)을 이용하여 분말 형태의 규소(Si)와 염화니켈 수화물 $(NiCl_2{\cdot}6H_2O)$을 혼합한 후 탄소공급원인 $CH_4$ 가스를 주입하여 탄화규소 나노선(SiC nanowire)을 합성하였다. 합성 온도와 $CH_4$ 가스 유량 변화에 따른 탄화규소 나노선의 구조적 특성을 분석한 결과, 합성온도가 $1,400^{\circ}C$, $CH_4$ 가스의 유량이 300 sccm인 경우가 탄화규소 나노선의 합성에 최적화된 조건임을 라만 분광법(Raman spectroscopy)과 X-선 회절(X-ray diffraction), 주사전자현미경(scanning electron microscopy), 그리고 투과전자현미경(transmission electron microscopy) 분석을 통해 확인하였다. 합성된 탄화규소 나노선의 직경은 약 50~150 nm이며, 곧은 방향성과 높은 결정성을 가지는 입방구조(cubic structure)를 지니고 있었다.

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.

층류 예혼합 화염의 화염 날림 현상에 미치는 교류 전기장 효과

김환호(H. H. Kim),김민국(M. K. Kim),정석호(S. H. Chung) 한국연소학회 2009 KOSCOSYMPOSIUM논문집 Vol.- No.39

The stabilization of the laminar premixed jet flames has been investigated experimentally by applying the AC electric fields at low frequency which is below 60㎐ in single electrode configuration. The detachment and blow off velocities have been measured by varying the applied AC voltage and frequency. The detachment velocity was decreased with the applied AC electric fields. The normalized velocity was changed linearly with AC voltage. The normalized velocity decreased and increased over certain frequency with AC frequency. Blowoff velocity had minimum value and transition frequency region was observed. Two different regimes were classified within the boundaries of minimum frequency and transition frequency region. In regime L-Ⅰ from 0.1㎐ to minimum frequency, blowoff velocity decreases with the applied frequency and decreasing rate increases. In regime L-Ⅱ from minimum frequency to transition frequency region, blowoff velocity has opposite trend to the regime L-Ⅰ. Ionic wind effect and chemical reaction enhancement are proposed as the possible causes to influence flame stabilization.

예혼합 분젠 화염의 안정화에 미치는 직류 전기장 효과

김환호(H. H. Kim),김민국(M. K. Kim),정석호(S. H. Chung) 한국연소학회 2010 KOSCOSYMPOSIUM논문집 Vol.- No.40

The effect of DC electric fields on the stabilization of the laminar premixed jet flames has been investigated with ground-mesh and in single-electrode configuration. The detachment velocities were measured by varying the applied positive and negative DC voltage at various distance of ground-mesh. The detachment velocity was increased and decreased with the magnitude of negative and positive DC voltage, respectively. As compared to the case of single-electrode configuration, the effect of DC voltage on the variation of detachment velocity with ground-mesh was appreciable. The variation of detachment velocity of premixed jet flame was well correlated by the representative strength of DC electric fields. It was observed that the effect of negative DC electric fields is larger than that of positive field. With qualitative evaluation of electric field, it was shown that the strength exerted on flame zone for negative DC source could be larger than that of for positive one. Consequently, the changes of detachment velocity with variation of applied DC voltage, distance of ground-mesh, and polarity of DC source were explained by the evaluated electric field strength.

대향류 확산화염의 소염특성에 미치는 직류전기장의 영향에 관한 실험적 연구

박익형(I. H. Park),김민국(M. K. Kim),원상희(S. H. Won),차민석(M. S. Cha),정석호(S. H. Chung) 한국연소학회 2006 KOSCOSYMPOSIUM논문집 Vol.- No.-

The effect of DC electric fields on the flame extinction was investigated experimentally in counterflow configurations for the methane/oxygen/nitrogen diffusion flame. The electric fields was applied by connecting the high voltage and ground terminals to the upper and lower burners, respectively. In case of having electric fields, several modes of flame extinction was observed according to the electric field intensity and strain rate defined by the exit velocity. To visualize and characterize the flame structure and intensity, planar LIF technique was adopted for OH radicals. Consequently, several length scales, including the flame width, thickness, and height from the burner tip, were introduced to explain the various flame behaviors and to characterize the flame extinctions. It was found that the variation of flame width and the chemical reaction are strongly related to a critical electric field intensity, thus the various modes of diffusion flame extinction could be observed due to the electric fields.

Effect of Low Frequency AC Electric Fields on Counterflow Diffusion Flames

최병철(B. C. Choi),김형국(H. K. Kim),김민국(M. K. Kim),최재혁(J. H. Choi),정석호(S. H. Chung) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-

The effect of electric fields on the response of diffusion flames in a counterflow has been investigated experimentally by varying the voltage and frequency of AC. The result showed that the flame was stationary with high frequency above the threshold frequency. Below the threshold frequency, the flame oscillated by exhibiting near sinusoidal or complex behaviour. This oscillation can be attributed to the ionic wind effect by the generation of bulk flow, arising from the momentum transfer between neutral molecules and ions, where the ions in the flame were accelerated by the Lorentz.