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DNSs of the Ignition of a Lean n-Heptane/Air Mixture under SCCI Conditions : Chemical Aspects
Gwang Hyeon Yu(유광현),Minh Bau Luong,Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.5
The chemical aspects of thermally- and/or compositionally-stratified n-heptane/air mixture under HCCI conditions are examined to obtain the insight of the ignition process in HCCI combustion. Chemical explosive mode analysis (CEMA) is adopted to understand the spatial ignition characteristics of the lean n-heptane/air mixture by identifying controlling species and elementary reactions at different locations and times.
$Nd_{1-x}Ba_xFeO_{3-y}$계의 비화학량론과 물리적 성질에 관한 연구
장순호,유광현,김성진,최승철,장순호,Chang, Soon Ho,Yu, Gwang Hyeon,Kim, Seong Jin,Choe, Seung Cheol,Jang, Sun Ho 대한화학회 1994 대한화학회지 Vol.38 No.8
$Nd_{1-x}Ba_xFeO_{3-y}$계에 대한 각 조성의 시료를 1200$^{\circ}C$ 대기압하에서 반응물을 가열하여 합성하였고 X-선 분말 회절분석을 통하여 고용체가 합성되었음을 확인하였다. X-선 회절분석 결과 x = 0.00과 0.25는 팔면체장이 뒤틀린 orthoferrite형의 사방정계이며, x = 0.50과 0.75의 조성을 갖는 화합물은 단순입방정계이다. 고용체내의 Fe이온은 $Fe^{3+}$와 $Fe^{4+}$이온의 혼합원자가 상태로 존재하기 때문에 $Fe^{4+}$이온의 몰비와 산소공위로부터 비화학량론적 조성식들을 결정하였다. Mossbauer분광분석결과 A자리에 $Ca^{2+}$ 또는 $Sr^{2+}$ 이온이 치환된 계들과는 달리 $Ba^{2+}$ 이온이 치환된 화합물들은 $FeO_6$와 $FeO_4$ 뿐만 아니라 $FeO_5$이 5배위장이 형성됨을 알 수 있었다. 또한 x = 0.25와 0.50 조성들은 초상자성의 스펙트럼을 보이는데 이는 $Fe^{3+}$ 와 $Fe^{4+}$ 이온간의 강자성 상호작용을 하는 영역을 형성하기 때문이다. 모든 시료의 전기전도도는 반도성 범위에 속한다. 시료는 $O^{2-}$ 이온을 매개로 한 Fe 이온간의 전자전달과정에서 $Fe^{4+}$ 이온은 전자 받게 준위로 작용하기 때문에 $Fe^{4+}$이온이 증가함에 따라 전기전도도의 활성화에너지가 감소된다. A series of samples in the $Nd_{1-x}Ba_xFeO_{3-y}$ system has been prepared by heating the reactants to$1200^{\circ}C$ under an ambient atmosphere, and the solid solutions were identified by X-ray power diffraction analysis. The crystal systems of samples with x = 0.00 and 0.25 were found to be orthorhombic whose local symmetry is similiar to the distorted octahedral with orthoferrite type one, whereas those with x = 0.50 and 0.75 to be the cubic system. Since Fe ions in the solid solutions are a mixed valence state between $Fe^{3+}\;and\;Fe^{4+}$ ions, the nonstoichiometric chemical formulas could be determined from the mole ratio of $Fe^{4+}$ ion and oxygen vacacies. According to the Mossbauer spectroscopic analysis, the presence of 5-coordinated $FeO_5$ was evidenced only in the barium compounds along with $FeO_6,\;and\;FeO_4$, but not in the strontium and calcium compounds. The samples with x = 0.25 and 0.50 show a spectrum of superparamagnetism, which might be due to the formation of a domain of the ferromagnetic interaction between the $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical conductivities of all samples are within semiconducting range. Since the $Fe^{4+}$ ion acts as an electron acceptor level during the electron transfer between the Fe through intermediate $O^{2-}$ ions, the activation energy of the compounds decreases with the increment of $Fe^{4+}$ content.
A DNS Study of Ignition of a Lean PRF/Air Mixture under RCCI/SCCI Conditions
Minh Bau Luong,Gwang Hyeon Yu(유광현),Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.5
A comparative DNS study of the ignition characteristics of dual-fueled reactivity controlled compression ignition (RCCI) and stratification charge compression ignition (SCCI) is investigated using a 116-species reduced primary reference fuel(PRF) mechanism. It is found that the overall RCCI combustion is greatly enhanced and flexibly controlled, thereby significantly reducing the peak HRR. The negative temperature coefficient has a synergistic effect on advancing the overall combustion and smoothing RCCI/SCCI combustion by inducing more low-speed deflagrations. Compared to SCCI, the overall combustion of RCCI is more advanced in time regardless of T0. However, it is also found that the effects of reactivity and/or equivalence ratio stratifications on reducing the peak are nearly eliminated with T0 in the high temperature regime for both RCCI/SCCI due to the dominant spontaneous ignition mode.
A DNS Study of RCCI Combustion
Minh Bau Luong,Gwang Hyeon Yu(유광현),Chun Sang Yoo(유춘상) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.12
The chemical aspects of primary reference fuel (PRF)/air mixture under RCCI conditions are investigated to provide fundamental insights into the ignition characteristics of RCCI combustion. Chemical explosive mode analysis (CEMA) is adopted to understand the ignition process of the lean PRF/air mixture by identifying controlling species and elementary reactions at different locations and times.
박새암(Park, Sae-Am),유광현(Yu, Gwang-Hyeon),유남재(Yoo, Nam-Jae) 강원대학교 산업기술연구소 2015 産業技術硏究 Vol.35 No.1
This paper is research results of the case study on analyzing the characteristics of debris flow considering forest environmental factors, focusing on occurrence of landslides around Mt. Daeryoung in 2013. Extensive landslide of debris flow, caused by heavy rainfall, occurred around Mt. Daeryoung during July in 2013. Field investigation was carried out to construct the data base about forest environmental factor including topography, soil formations and forest type. Thus, contributing factors to cause the landslide of debris flow were investigated so that damages from landslides could be reduced by establishing proper measures.