• 한국수소및신에너지학회논문집
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• 제13권3호
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• pp.169-180
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• 2002

Rayleigh scattering and laser induced predissociative fluorescence are used to obtain two-dimensional images of temperature and species concentration in a laminar non-premixed flame of a diluted hydrogen jet. Rayleigh scattering cross-sections are experimentally obtained at 248nm. Planar images of OH and $O_2$ with tunable KrF excimer laser which has a) $0.5cm^{-1}$ linewidth, b) 0.5nm tuning range, c) 150mJ pulse energy, and d) 20ns pulse width are obtained to determine spatial distributions of OH and $O_2$. The technique is based on planar laser induced predissociative fluorescence (PLIPF) in which collisional quenching is almost avoided because of the fast predissociation. Dispersed LIPF spectra of OH and $O_2$ are also measured in a flame in order to confirm the excitation of single vibronic state of OH and $O_2$. OH and $O_2$ are excited on the $P_2$(8) and $Q_1$(11) line of the $A^2{\Sigma}^{+}({\nu}^{'}=3)-X^{2}{\Pi}({\nu}^{''}=o)$ band and R(17) line of the Schumann-Runge band $B^{3}{\Sigma}_{u}{^-}(\nu^{'}=0)-X^{3}{\Sigma}_{g}{^-}({\nu}^{''}=6)$, respectively. Fluorescence spectra of OH and Hot $O_2$ are captured and two-dimensional images of the hydrogen flame field are successfully visualized.

• 한국응용과학기술학회지
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• 제35권3호
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• pp.865-875
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• 2018

식물성 오일을 이용한 바이오 항공유의 제조공정에서 탈산소 반응의 적절한 운전조건 선정을 통한 생성물 물성 최적화는 최대의 바이오항공유 수율을 얻기 위해 필수적인 요소이다. 이에 따라 팜유의 탈산소화 반응이 1 wt.% $Pt/Al_2O_3$촉매가 장입된 내경이 1인치인 고정층 반응기에서 수행되었다. 업그레이딩 공정을 통하여 수송 연료로 활용될 수 있는 액체 생성물(organic liquid product)은 가스크로마토그래피 방법으로 그 조성을 분석하였다. 피드 내의 팜유/수소 비율과 수소 압력은 탈카르복실레이션과 수첨탈산소 반응에 영향을 주어 생성물의 조성 변화를 초래하였다. 반응 온도가 증가함에 따라 탈산소 생성물의 연속적 크래킹 반응이 촉진되어 $C_5{\sim}C_{14}$영역의 생성물 조성이 증가하였다. 본 연구의 결과는 팜유의 탈산소화 반응 특성의 이해 뿐 아니라 연속 공정인 수첨 업그레이딩 공정을 통한 바이오 항공유의 제조에 도움을 줄 수 있다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.121-128
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• 2009

During a hypothetical high-pressure accident in a nuclear power plant (NPP), molten corium can be ejected through a breach of a reactor pressure vessel (RPV) and dispersed by a following jet of a high-pressure steam in the RPV. The dispersed corium is fragmented into smaller droplets in a reactor cavity of the NPP by the steam jet and released into other compartments of the NPP by a overpressure in the cavity. The fragments of the corium transfer thermal energy to the ambient air in the containment or interact chemically with steam and generate hydrogen which may be burnt in the containment. The thermal loads from the ejected molten corium on the containment which is called direct containment heating (DCH) can threaten the integrity of the containment. DCH in a NPP containment is related to many physical phenomena such as multi-phase hydrodynamics, thermodynamics and chemical process. In the evaluation of the DCH load, the melt dispersion rates depending on the RPV pressure are the most important parameter. Mostly, DCH was evaluated by using lumped-analysis codes with some correlations obtained from experiments for the dispersion rates. In this study, MC3D code was used to evaluate the dispersion rates in the APR1400 NPP during the high-pressure accidents. MC3D is a two-phase analysis code based on Eulerian four-fields for melt jet, melt droplets, gas and water. The dispersion rates of the corium melt depending on the RPV pressure were obtained from the MC3D analyses and the values specific to the APR1400 cavity geometry were compared to a currently available correlation.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• 한국연소학회지
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• 제14권1호
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• pp.31-38
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• 2009

The effects of acoustic excitation of coaxial air on mixing enhancement and reduction of nitrogen oxides (NOx) emission were investigated. A compression driver was attached to the coaxial air supply tube to impose excitation. Measurements of NOx emission with frequency sweeping were performed to observe the trend of NOx emission according to the fuel and air flow conditions and to inquire about the effective excitation frequency for reducing NOx. Then, Schlieren photographs were taken to visualize the flow field and to study the effect of excitation. In addition, phase-locked particle image velocimetry (PIV) was performed to acquire velocity field for each case and to investigate the effect of vortices more clearly. Direct photographs and OH chemiluminescence photographs were taken to study the variation of flame length and reaction zone. It was found that acoustic forcing frequencies close to the resonance frequencies of coaxial air supply tube could reduce NOx emission. This NOx reduction was influenced by mixing enhancement due to large-scale vortices formed by fluctuation of coaxial air jet velocity.

• 한국연소학회지
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• 제7권1호
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• pp.1-7
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• 2002

Experiments have been performed to investigate the structure of axisymmetric hydrogen diffusion flame in a supersonic coflow air. The characteristics and structure of supersonic flames are compared with those of subsonic flames as the velocity of coflow air increases from subsonic to supersonic velocity of Mach 1.8. Also, the subsonic and supersonic flow fields are analyzed numerically for the non-reacting conditions and the possible flame contours indicated by fuel mass fraction are compared with the measured OH radical distributions. It is found that the flame structure indicates more like a partially premixed flame as the coflow air velocity is increased from subsonic to supersonic regimes; strong reaction zone indicated by intense OH signal is found at the center, which is different from subsonic flame cases. And it is shown that the fuel jet passes along the recirculation zones behind the bluff-body fuel nozzle resulting in relatively long mixing time. This is believed to be the reason of the partially premixed flame characteristics found in the present supersonic flames.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1582-1582
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• 2000

Rayleigh scattering and laser induced predissociative fluorescence are employed for capturing two-dimensional images of temperature and species concentration in a laminar nonpremixed flame of a diluted hydrogen jet. Rayleigh scattering cross-sections are experimentally obtained at 248nm. Dispersed LIPF spectra of OH and O₂ are also measured in a flame in order to confirm the excitation of single vibronic state of OH and O₂are excited on the P₁(8) line of the A ²∑+ (v＇=3) - X ²∏(v˝=0) band and R(17) line of the Schumann-Runge band B ³∑u- (v＇=0) - X ³∑g-∏(v˝=6), respectively. Fluorescence spectra of OH and Hot O₂ are captured and two-dimensional images of the hydrogen flame field are successfully visualized.

• 에너지공학
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• 제26권4호
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• pp.7-13
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• 2017

환경문제가 생존문제로까지 부각되면서 대기환경 개선을 위해 친환경에너지에 대한 관심이 높아져 그에 따른 환경 친화적 연료인 수소, LPG, CNG에 대한 수요가 점차 증가하고 있는 추세이다. 특히, 대부분의 연료를 수입에 의존하고 있는 우리나라의 경우 높은 생산량과 에너지 자립적 측면에서 유리한 위치에 있는 수소 에너지의 개발에 투자를 아끼지 않고 있는 상황이다. 하지만 매년 증가하고 있는 수요만큼 작은 누출사고부터 대형 화재 폭발사고까지 충전소사고 또한 다양하게 발생하고 있기 때문에 그에 대한 연구가 필요하다. 따라서 본 연구에서는 국내 외 충전소에서 발생하는 수소, LPG, CNG의 사고 사례들을 비교 분석하였고 위험성평가를 위한 다양한 프로그램을 사용해 가스누출에 의한 피해거리를 예측하고 위험거리를 평가하였다.

• 한국수소및신에너지학회논문집
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• 제25권1호
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• pp.47-58
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• 2014

The characteristics of flame shape, laminar burning velocity, emissions and heat flux of stagnation point in premixed impinging jet flame of syngas fuel with 10% hydrogen content were experimentally investigated. Also, the adiabatic temperature and burning velocity are calculated by Chemkin package with USC-II mechanism. The equivalence ratios(0.8~5.0) and dimensionless separation distance(2.0~5.0) with fixed Reynolds number(1800) are main parameters in this work. Different flame shapes and colors were observed for different impingement conditions. The experimental results of burning velocity by flame surface area have a consistent with previous works and numerical simulation of this work. The inner flame length could be predicted with the ratio of mixture velocity and burning velocity from a simple formulation by the laminar burning velocity definition. It has been observed that the heat fluxes at stagnation point are directly affected by the flame shape including the separation distance. The emission results in impinging flame of syngas fuel show that the characteristics of $NO_x$ emission traced well with adiabatic temperature trend and CO emission due to fuel rich condition increased continuously with respect to the equivalence ratio.

• 한국수소및신에너지학회논문집
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• 제25권1호
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• pp.59-71
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• 2014

An experimental study has been conducted to investigate the heat transfer characteristics of laminar syngas/air mixture with 10% hydrogen content impinging normally to a flat plate of cylinder. Effects of impinging distance, Reynolds number and equivalence ratio as major parameters on heat fluxes of stagnation point and radial direction were examined experimentally by the direct photos and data acquisitions from heat flux sensor. In this work, we could find the incurved flame behavior of line shaped inner top-flame in very closed distance between flat plate and burner exit, which has been not reported from general gas-fuels. There were 3 times of maximum and 2 times minimum heat flux of stagnation point with respect to the impinging distance for the investigation of Reynolds number and equivalence ratio effect. It was confirmed that the maximum heat flux of stagnation point in 1'st and 2'nd peaks increased with the increase of the Reynolds number due to the Nusselt number increment. There was a third maximum rise in the heat flux of stagnation point for larger separation distances and this phenomenon was different each for laminar and turbulent condition. The heat transfer characteristics between the stagnation and wall jet region in radial heat flux profiles was investigated by the averaged heat flux value. It has been observed that the values of averaged heat flux traced well with the characteristics of major parameters and the decreasing of averaged heat flux was coincided with the decreasing trend of adiabatic temperature in spite of the same flow condition, especially for impinging distance and equivalence ratio effects.