• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3282-3287
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• 2007

Lean combustion is one of the most promising method for increasing engine efficiency and reducing the exhaust emission from SI gas engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate are needed to guarantee a successful subsequent combustion. Experiment data were obtained on a single-cylinder CNG fueled SI engine to investigate the effect of direct injection, spark timing and variation of injection timing. Experimental results show that lean burn limit is ${\lambda}$=1.3 with port injection, and expansion of lean burn limit ${\lambda}$=1.4 with direct injection method, due to increase of turbulence intensity in cylinder and stratified charge. Combustion duration in lean region is improved by using the variation of injection timing.

• International Journal of Automotive Technology
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• 제5권4호
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• pp.239-245
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• 2004

It has been recognized that alternative fuels such as Liquid Petroleum Gas (LPG) show less polluting combustion characteristics than diesel fuel. Furthermore, engine performance is expected to be nearly equal to that of the diesel engine if direct-injection stratified-charge combustion of the LPG can be adopted in the spark-ignition engine. However, spray characteristics of LPG are quite different from those of diesel fuel. understanding the spray characteristics of LPG and evaporating processes are very important for developing efficient and low emission LPG engines optimized in fuel injection control and combustion processes. In this study, the LPG spray characteristics and evaporating processes were investigated using the Schlieren and Mie scattering optical system and single-hole injectors in a constant volume chamber. The results show that the mixture moves along the impingement wall that reproduced the piston bowl and reaches in ignition spark plug. LPG spray receives more influence of ambient pressure and temperature significantly than that of n-dodecane spray.

• 한국자동차공학회논문집
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• 제7권5호
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• pp.22-30
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• 1999

Optimization of in-cylinder flow is regarded as one of the most important factors to realize stable stratified charge combustion in a Spark-ignited Direct Injection(SDI) engine. Therefore, Computational Fluid Dynamic(CFD) simulation technique were used to clarify the characteristics of in-cylinder flow of a SDI engine with top entry intake port. Also, CFD results were compared to experimental results using Laser Doppler Velocimetry(LDV), Particle Image Velocimetry(PIV) and good validations were met. As the results reverse tumble flow generated during intake process was preserved by configuration of curved piston while base and reverse tumbles were diminished at the end of compression stroke in case of flat top piston. In addition, it will be needed to optimize the fuel mixture distribution based on these results.

• 대한기계학회논문집B
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• 제34권12호
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• pp.1035-1042
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• 2010

HCCI 엔진연소에서 열적성층화 효과는 노킹을 회피하는 수단으로서 생각되고 있다. 본 연구에서는 DME 와 n-Butane 을 연료로 하는 HCCI 엔진연소의 열적성층화 효과를 조사하였다. 예혼합기가 연소실내부에 투입되고 부력의 효과를 이용하여 연소실 내부에 열적성층화를 형성한다. 그 뒤에 피스톤의 압축에 의해서 단열압축 시킨 후 연소실압력과 2 차원화학발광법을 계측하여 해석하였다. 열적성층화가 존재하는 경우에는, 저온산화반응과 고온산화반응의 시작시기가 균질한 경우에 비해서 진각되었고 연소기간은 길어졌다. 발광의 시작은 온도가 높은 곳에서부터 시작하여 온도가 낮은 곳으로 전파 되는 것을 확인하였고 발광기간도 길어짐을 확인하였다.

• 보건행정학회지
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• 제28권1호
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• pp.53-69
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• 2018

Background: This study investigates association modified category medical specialization (CMS) and hospital charge, length of stay (LOS), and mortality among lumbar spine disease inpatients. Methods: This study used National Health Insurance Service-cohort sample database from 2002 to 2013, using stratified representative sampling released by the National Health Insurance Service. A total of 56,622 samples were analyzed. The primary analysis was based on generalized estimating equation model accounting for correlation among individuals within each hospital. Results: Inpatients admitted with lumbar spine disease at hospitals with higher modified CMS had a shorter LOS (estimate, -1.700; 95% confidence interval [CI], -1.886 to -1.514; p<0.0001). Inpatients admitted with lumbar spine disease at hospitals with higher modified CMS had a lower mortality rate (odds ratio, 0.635; 95% CI, 0.521 to 0.775; p<0.0001). Inpatients admitted with lumbar spine disease at hospitals with higher modified CMS had higher hospital cost per case (estimate, 192,658 Korean won; 95% CI, 125,701 to 259,614; p<0.0001). However, inpatients admitted with lumbar spine surgery patients at hospitals with higher modified CMS had lower hospital cost per case (estimate, -152,060 Korean won; 95% CI, -287,236 to -16,884; p=0.028). Inpatients admitted with lumbar spine disease at hospitals with higher modified CMS had higher hospital cost per diem (estimate, 55,694 Korean won; 95% CI, 46,205 to 65,183; p<0.0001). Conclusion: Our results showed that increase in hospital specialization had a substantial effect on decrease in hospital cost per case, LOS, and mortality, and on increase in hospital cost per diem among lumbar spine disease surgery patients.

• 한국분무공학회지
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• 제13권1호
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• pp.1-8
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• 2008

It was investigated how fuel injection timing - early injection and later injection - in conjunction with throttle open rate effect the fuel-air mixing characteristics, Engine power, combustion stability and emission characteristics on a DI CNG spark Engine and control system that had been modified and designed according to the author's original idea. It was verified that the combustion characteristics were changed according to fuel injection timings and Engine conditions determined by different throttle open rates and rpm. It was found that the combustion characteristics greatly improved at the complete open throttle rate with an early injection timing and at the part throttle rate with a late injection timing. Combustion duration was governed by flame propagation duration in a late injection timing and by an early flame development duration in an early injection timing. As the result, we discovered that combustion duration is shortened, lean limit is improved, air-fuel mixing conditions controlled, and emissions reduced through control of fuel injection timing according to change of the throttle open rate.

• 동력기계공학회지
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• 제18권6호
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• pp.186-192
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• 2014

The spray structures under the stratified and homogeneous charge condition of a gasoline direct injection were investigated in a visualized constant volume chamber. The chamber pressure was controlled from 0.1 MPa to 0.9 MPa by the high pressure nitrogen and the chamber temperatures of $25^{\circ}C$, $60^{\circ}C$ and $80^{\circ}C$ were controlled by the band type heater. The fuel, iso-octane was injected by a 6-hole injector with the pressures of 7 MPa and 12 MPa. From the experiments results, it is confirmed that at lower chamber pressure, the penetration length and spray angle are mainly affected by the chamber temperature with the vaporization of the fuel droplets and generated vortices at the end region of the spray. And at higher chamber pressure, the penetration lengths at the end of the injection were about 50~60% of that at lower chamber pressure regardless of the chamber temperature and the effect of fuel injection pressure is larger than that of the chamber temperature which results from larger penetration lengths at higher fuel injection pressure than at lower fuel injection pressure regardless of the chamber temperatures.

• 한국보건간호학회지
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• 제3권1호
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• pp.5-17
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• 1989

The purpose of this study was to investigate the natural menopause age of middle-aged women in Korea and to analyse various factors affecting them. For the collection of date, 1,140 women aged between 45-54 were selected through stratified sampling technics in Seoul and at a rual area in Kyong KiProvince. They were interviewed from Nov. 1 through Dec. 31,1987 by use of questionnaires made after pilot study had been performed twice. Among them the final subjects for analysis were restricted to only those who had experienced menopause or irregular menstruation during the past one year, the number of which was total 410:206 in urban and 204 in rural area. For the analysis, menopause age was used as dependent variables while fertility variables, socio-economic variables, bio-physical varibles, and insight of life variables were classified as independent variables. Dependent variables such as menopause was tested and analysed by descriptive statistical methods(e.g., frequency, percentage, mean, $X^2-test.$ t-test, ANOVA). The relation between menopause age and independent variables was analysed by use of Pearson's correlation coefficients. For the analysis of various factors affecting menopause age, multiple stepwise regression method was used. The obtained results are summarized as follows: 1. The natural menopause age of Korean women were 47.2 mean age: it was 47.7 and 46.7 mean age in urban and rural area respectively, which revealed that the former was later then the latter by one year. And the recollective error on menopause starting age between the menopause group and the group who had experienced irregular menstruation during the past one year was 0.4-0.7 year. 2. The main factors affecting the menopause age were (1) the duration of marital life, (2) the duration of oral pill use, (3) insight of life and economic status, (4) educational background. (5) menarche, (6) usual menstruation amount, (7) electic charge. and (8) area. These factors. altogether, could explain $18.4\%$ of factors related with menopause, and they took the high percentage in the order mentioned.

• 동력기계공학회지
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• 제12권4호
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• pp.5-11
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• 2008

The RI gasoline engine haying a sub-chamber had a high cycle variation due to the difficulty of the residual gas scavenge in the sub-chamber. To solve this problem and improve the combustion performance of RI engine, we devised a method to inject directly CNG fuel into the sub-chamber. A DI diesel engine of single cylinder was converted into a RI-CNG engine and an electronic control unit for the engine was manufactured. In this study, the combustion characteristics of the RI-CNG engine were investigated with the injection timings and air excess ratios at the load conditions of 50% throttle open rate and 1700rpm. As the results from this study, the RI-CNG engine worked reliably under the condition of the ignitable lean limit of $\lambda=1.7$ by showing the $COV_{imep}$ below about 5%. And the highest thermal efficiency could be obtained in the injection timing that produced the high imep and the low $COV_{imep}$ at the same time. The CO emission concentration indicated very low values and the THC and $NO_x$ showed an opposite pattern. With a view to improving the thermal efficiency and reducing the harmful emissions, the proper control region of the ignition timing and the mixture ratio were nearly ATDC $20^{\circ}\sim50^{\circ}$ and $\lambda=1.4$ respectively.

• 한국가스학회지
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• 제20권1호
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• pp.52-61
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• 2016

액화석유가스는 환경 친화적이며 에너지 효율성과 출력성능이 뛰어나 실용성이 높고, 경쟁연료에 비해 가격 경쟁력이 우수하기 때문에 촉망받는 대체연료 중 하나로 간주된다. 스파크점화 엔진에서 직분식 기술은 엔진 체적효율을 눈에 띄게 증가시키며, 상대적으로 더 높은 연소효율이 가능한 성층급기를 이용해 엔진을 작동시킨다. 본 연구에서는 가솔린직접분사 엔진의 원리를 적용하여 가시화 시스템을 장착한 연소실을 설계하였다. 이를 통해 스파크점화직분식 LPG의 점화성과 화염전파 과정을 디지털 방식으로 기록하고 분석하였다. 이러한 연구의 결과는 스파크점화직분식 LPG 엔진의 설계 및 최적화를 위한 광범위한 기초 자료로서 기여하고자 한다.