• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.272-275
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• 2008

One of the important operating factors for the air-fuel pre-mixed conditions in an HCCI engine is an in-cylinder flow. In this study, unsteady in-cylinder air flow characteristics in a diesel engine as a reference engine of an HCCI engine development were numerically analysed. Unsteady flow analyses were conducted with the combination of 3 intake port inlets, then the in-cylinder air flow distribution and swirl ratio results from a case were compared with the results from the other cases.

• Korean Journal of Veterinary Research
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• v.15 no.1
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• pp.27-38
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• 1975

The following tumors occurring naturally in the dog were studied pathologically and discussed briefly. Tumors of the skin and subcutis: Fibroma, Lipoma, Epidermal cyst, Melanosarcoma, Sweat gland adenoma, Mastocytoma (2 cases), Mastosarcoma, and Sebaceous gland carcinoma. Tumors of the spleen and lymph node: Fibrosarcoma of the capsule of spleen, Leiomysarcoma of the spleen, and Lymphosarcoma of the lymph node (2 cases). Tumors of the lung: Bronchogenic carcinoma (3 cases), Adenocarcinoma type, Squamous carcinoma type, and Undifferentiated (round cell) carcinoma type respectively. Tumors of the alimentary tract and liver: Fibroma of the stomach, Hemangioma of the liver, Bile duct carcinoma, Liver cell carcinoma, and Myelogenous leukemia manifested in the liver. Tumor of the peritoneum: Fibrosarcoma. Tumors of the urogenital system: Fibroma of the uterus, Fibroma of the prepuce, Follicular cyst of the ovary, Transmissible venereal tumor of the vagina (6 cases), Carcinoma of the kidney, Adenoma of the prostate (2 cases), and Seminoma of the testis. Tumors of the mammary gland: Mixed tumor (2 cases), and Myoepithelioma. Tumor of the nervous system: Neurofibrosarcoma of the thigh.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.933-938
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• 2011

In this study, the heat transfer characteristics and NOx and CO emissions of a heat exchanger were investigated using a premixed burner. The experiments involved changing the distance between the burner and heat exchanger to 30, 40, and 50 mm with various equivalence ratios. The results showed that the NOx and CO emissions increased as the equivalence ratio was increased because the flame temperature increased, regardless of the distance between the burner and heat exchanger. In particular, the CO emission increased significantly as the distance between the burner and heat exchanger was decreased. The optimal equivalence ratio for the A-type heat exchanger (distance between the burner and heat exchanger: 30 cm) was 0.7 in the experimental range. In this case, the CO and NOx emissions were 94.5 ppm and 11.2 ppm, respectively, and the efficiency was 84.1%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.735-742
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• 2011

A catalytic burner that utilizes the thermal energy from fossil fuels without the emission of nitrogen oxides ($NO_x$) has been developed. For this purpose, the newly developed burner has two features: firstly, it is in the shape of a flat mat so as to maximize its heating surface, and secondly, it adopts premixed combustion so that it can be used in a closed space. In the present study, the burner was used in a radiation-type industrial dryer. This dryer yields thermal energy in the form of thermal radiation in the infrared regime, which has been proved to be effective for drying organic substances under low-moisture conditions. Analysis of the experimental data has proved that the thermal efficiency of the dryer is better correlated to the moisture than to the dry rate

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.21-30
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• 2000

Numerical design optimization techniques are implemented for the improvement of the ram accelerator performance. The design object is to find the minimum ram tube length required to accelerate projectile from initial velocity $V_o$ to target velocity $V_e$. The premixture is composed of $H_2$, $O_2$, $N_2$ and the mole numbers of these species are selected as design variables. The objective function and the constraints are linearized during the optimization process and gradient-based Simplex method and SLP(Sequential Linear Programming) have been employed. With the assumption of two dimensional inviscid flow for internal flow field, the analyses of the nonequilibrium chemical reactions for 8 steps 7 species have been performed. To determined the tube length, ram tube internal flow field is assumed to be in a quasi-steady state and the flow velocity is divided into several subregions with equal interval. Hence the thrust coefficients and accelerations for corresponding subregions are obtained and integrated for the whole velocity region. With the proposed design optimization techniques, the total ram tube length had been reduced 19% within 7 design iterations. This optimization procedure can be directly applied to the multi-stage, multi-premixture ram accelerator design optimization problems.

• Journal of Hydrogen and New Energy
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• v.24 no.6
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• pp.573-579
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• 2013

Hydrogen engine with homogeneous charged compression ignition can achieve high efficiency by high compression ratio and rapid chemical reaction rates spatially. However, it needs to expansion of the operation range with over-all load conditions which is very narrow due to extremely high pressure rise rate. The adoption of the lean boosting in a HCCI $H_2$ engine is expected to be effective in expansion of operation range since minimum compression ratio for spontaneous ignition is decreased by low temperature combustion and increased surround in-cylinder pressure. In order to grasp its possibility by using lean boosting in the HCCI $H_2$ engine, compression ratio required for spontaneous ignition, expansion degree of the operation range and over-all engine performance are experimentally analyzed with the boosting pressure and supply energy. As the results, it is found that minimum compression ratio for spontaneous ignition is down to the compression ratio(${\varepsilon}$=19) of conventional diesel engine due to decreased self-ignition temperature, and operation range is extended to 170% in term of the equivalence ratio and 12 times in term of the supply energy than that of naturally aspirated type. Though indicated thermal efficiency is decreased by reduced compression ratio, it is over at least 46%.

• Journal of Hydrogen and New Energy
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• v.18 no.1
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• pp.75-84
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• 2007

The effects of hydrogen enrichment to methane on NOx formation have been investigated with swirl stabilized pre-mixed hydrogen enriched methane flame in a laboratory-scale pre-mixed combustor(nominally of 5,000 kcal/hr). The hydrogen enriched methane fuel and air were mixed in a pre-mixer and introduced to the combustor through different degrees of swirl vanes. The flame stability was examined for different amount of hydrogen addition to the methane fuel, different combustion air flow rates and swirl strengths by comparing equivalence ratio at the lean flame limit. The hydrogen addition effects and swirl intensity on the combustion characteristics of pre-mixed methane flames were examined using gas analyzers, and OH chemiluminescence techniques to provide information about species concentration of emission gases and flowfield. The results of NOx and CO emissions were compared with a diffusion flame type combustor. The results show that the lean stability limit depends on the amount of hydrogen addition and the swirl intensity. The lean stability limit is extended by hydrogen addition, and is reduced for higher swirl intensity at lower equivalence ratio. The addition of hydrogen increases the NOx emission, however, this effect can be reduced by increasing either the excess air or swirl intensity. The NOx emission of hydrogen enriched methane premixed flame was lower than the corresponding diffusion flame under the fuel lean condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.41-46
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• 2018

In this research, numerical analysis was performed to determine the effects of hydrogen on biogas combustion for homogeneous charged compression ignition (HCCI) engines. The target engine specifications were a 2300cc displacement volume, 13:1 compression ratio, 15kW of electricity, and 1.2 bar boost pressure. The engine speed was fixed to 1800rpm. By varying the excess air ratio and hydrogen contents, the cylinder pressure, nitric oxide, and carbon dioxide were measured as a function of the hydrogen contents. According to preliminary studies related to the reaction mechanism for methane combustion and oxidation, a GRI 3.0 mechanism as the base mechanism was selected for HCCI combustion calculations describing the detailed reaction mechanism. By adding hydrogen, NO was increased while $CO_2$ was decreased. The cylinder pressure was also increased, having advanced timing for the maximum cylinder pressure and pressure rise region. Furthermore, lean operation limits were extended by adding hydrogen to the HCCI engine.

• Journal of the KSME
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• v.34 no.9
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• pp.688-697
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• 1994

유체유동이나 열전달 그리고 물질전달 (물질의 혼합 및 확산) 또는 이들 현상이 복합적으로 나 타나는 각종 기계의 설계와 성능 해석을 하기 위해서는 그 현상을 지배하는 편미분 방정식들의 해를 수치적으로 구해야 한다. 유동 상태가 충류 유동인 경우는 지배 방정식의 수가 알고자 하는 미지변수 즉 속도, 압력, 온도, 농도 등의 개수와 같고 또한 이들 변수들의 변동이 그리 심하지 않기 때문에 적절한 수치 해법을 사용하면 그 해를 구할 수 있다. 그러나 난류유동의 경우에는 변수들이 시간상으로 또한 공간적으로 대단히 심하게 변동(fluctuation)하기 때문에 공 학적으로 우리가 원하는 정보들, 즉, 표면 마찰저항이나 양력, 얼전달 계수, 물질 확산계수 등을 현재 수준의 전자계산기로 계산하는 데는 계산시간이 엄청나게 소요될 뿐만 아니라 변수 저장 메모리도 과도하게 차지하기 때문에 실제적인 계산 방법이 되지 못하고 있다. 이러한 이유로 변수들의 순간 변화 상태를 나타내는 지배 방정식들을 해석하는 대신에 이들 지배 방정식의 시 간평균을 취하여 유도한 난류 방정식들을 사용하게 된다. 그러나 이 시간 평균 과정에서 파생 되는 또 다른 미지의 난류 변수들 때문에 난류 지배 방정식에 있어서는 그 지배 방정식의 개수 보다 미지 변수의 개수가 많아져서 난류 지배 방정식을 풀기 위해서는 시간평균 과정에서 나타난 난류 변수들을 원래 있던 미지 변수들의 함수나 방정식의 형태로 가정할 필요가 있게 되는데 이 가정되는 함수 관계들을 난류 계산 모형이라고 한다. 난류 계산 모형은 물리적인 통찰과 직관에 의해서 실용적인 형태로 가정되기도 하지만 최근에는 논리적으로 엄격한 모형 원칙에 따른 수 학적인 방법으로 유도되고 있는데 이 글에서는 일반 독자들이 쉽게 이해할 수 있도록 마하수가 낮은 2차원 비압축성 난류 유동을 예로 들어 x-y 직교 좌표계에서 표현되는 난류 계산 모형들을 소개하고 앞으로듸 발전 방향을 개관하며 현재의 응용 사례들을 예로 들어 모형의 성능을 비교 하여 보기로 한다.

• Korean Journal of Head & Neck Oncology
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• v.28 no.2
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• pp.146-148
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• 2012

후두낭종은 후두소낭의 비정상적인 팽창으로 발생하는 드문 질환이다. 후두낭종의 크기와 증상에 따라 치료 방법은 단순 경과관찰에서부터 흡인, 경화제 주입, 수술적 치료까지 다양하다. 수술적 치료는 외적 접근법, 내시경적 접근법 또는 두 접근법을 혼용한 접근법을 통해 이루어진다. 최근 저자들은 경부 외적 접근법 및 연골막하 절제를 통한 혼합 후두점액낭종 1예의 치료를 경험하였기에 문헌 고찰과 함께 보고하는 바이다.