• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.465-471
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• 2006

Controlled auto-ignition(CAI) combustion, offers the potential to improve fuel economy and reduce emission simultaneously. In this study, CAI-combustion was achieved in a single cylinder gasoline DI engine with modified camshafts in order to restrict the gas exchange process. We investigated the effects of air-fuel ratio, residual EGR rate and injection timing such as early injection and late injection on the attainable CAI combustion region. The effect of injection timings on combustion characteristic such as start of combustion, combustion duration and heat release rate was also investigated. From the result early injection causes the mixture to ignite earlier and burn more quickly due to the exothermic reaction during the recompression and gives rise to good mixing of the fuel/air. On the other hand, late injection extended the operation region more than early injection but the emissions of HC and NOx were more or less increased than early injection.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2477-2487
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• 2021

To improve safety analysis technology for a nuclear reactor containment considering an interaction between a reactor coolant system (RCS) and containment, this study aims at an experimental investigation on the integrated simulation of the RCS and containment, with an integral effect test facility, ATLAS-CUBE. For a realistic simulation of a pressure and temperature (P/T) transient, the containment simulation vessel was designed to preserve a volumetric scale equivalently to the RCS volume scale of ATLAS. Three test cases for a steam line break (SLB) transient were conducted with variation of the initial condition of the passive heat sink or the steam flow direction. The test results indicated a stratified behavior of the steam-gas mixture in the containment following a high-temperature steam injection in prior to the spray injection. The test case with a reduced heat transfer on the passive heat sink showed a faster increase of the P/T inside the containment. The effect of the steam flow direction was also investigated with respect to a multi-dimensional distribution of the local heat transfer on the passive heat sink. The integral effect test data obtained in this study will contribute to validating the evaluation methodology for mass and energy (M/E) and P/T transient of the containment.

• Journal of Life Science
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• v.15 no.3 s.70
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• pp.468-473
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• 2005

The coastal regions of Yeosu, the South Sea of Korea, has occurred annually the red tide which is caused by potentially ichthyotoxic dinoflagellate C. polykrikoides, with a wide avenue for exchange with oceanic waters and freshwater runoff from Sumjin river. We attempted to examine the variability in response to vertical migration and concentration of extracted DNA/RNA of C. polykrikoides exposed to salinity-stratified waters. The experimental aquarium of the 60 liter was employed to culture C. polykrikoides. One aquarium was supplied with only sea water, the other was consisted of sea water and freshwater. Experiment was conducted for 5 days. In experimental column (mixture of freshwater and sea water), salinity was maintained to 20 at upper and approximately 30 at bottom during the period of this study. The fluctuation with related to dissolved oxygen and pH was similar pattern to both columns. Chlorophyll a was significantly higher value at upper than bottom. During 24h, chlorphyll a on experimental column was extremely high on the top as soon as lighting, compared with control. With elapsed time, the gap between experimental and control columns was a little. In darkness, chlorophyll a was not significantly different between upper and bottom, most cells appeared to randomly distribute on column regardless of water layer. Fluctuation with related to concentration of extracted DNA and RNA based on ratio of absorbance of 260 and 280 nm in experimental column was higher at final day or diel migration than control. These results implied that a large volume of freshwater could be associated with influence of concentration of DNA and RNA, in particular, rapid upward movement caused massive fish kills as soon as sunset.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.981-987
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• 2011

In this study, single cylinder engine experiment was carried out to investigate combustion characteristics spray guided direct injection spark ignition engine. In the result of engine experiment, it was shown that flammable window of injection timing was existed. The combustion efficiency increased with retarding injection timing, reaching a peak value, subsequent to decrease again. These results were likely due to the effect of ambient pressure on stratified-premixed mixture preparation. 150 bar injection pressure condition and retarded injection timing from the best combustion efficiency injection timing showed the highest IMEP value due to the advanced combustion phase of the maximum combustion efficiency condition. HC emission showed same trend of combustion efficiency, and smoke emission was increased as injection timing was retarded due to the increased locally rich area in the high ambient pressure. NOx emission showed decreasing trend as injection timing was retarded. This is likely due to the maximum in-cylinder temperature was decreased with retarded combustion phase.

• The Research Journal of the Costume Culture
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• v.18 no.3
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• pp.423-435
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• 2010

The purpose of this study was to observe the current consumption of bedding products, purchase behavior, and to compare between purchase criteria and degree of satisfaction after the purchase. Independent variables are age, consumer's knowledge and involvement about the bedding materials. This study can contribute for bedding product marketing strategies and design development. We used questionnaires that were distributed to 500 females aged in 20s to 50s, using stratified sampling method. Only 457 reliable questionnaires were selected for statistical analysis. Data were analyzed statistically through frequencies, paired t-test, ANOVA, Dunnett T3, Chi-test, using SPSS (Version 12.0). The results of this study are as follows. The types of bedroom was significantly associated with age variables. Women in 20's to 30's were using the mixture of Ondol and bed(chimdaie), while 40's to 50's women were using bed for all their rooms. The usage of filling material for the comforter(ibul) was significantly associated with the age group. 20's to 30's age group preferred synthetic fibers for the filling, while 40 to 50's women preferred cotton fibers. Generally, the most of people used quilted comforter and they used cotton material as filling materials of comforters. As to purchase behavior, the most frequent place of purchase was specialty store of bedding products, and the highest percentage of motivation for purchase was "deformation after the use/throwing away". Purchase motivation for bedding was related with the age variable and the clusters based on the knowledge of bedding materials. We analysed the comparison test purchase criteria and satisfaction. In all attributes except brand image, people evaluated lower in satisfaction after purchase than in criteria before purchase.

• Journal of Power System Engineering
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• v.12 no.4
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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.

• Journal of the Korean Institute of Gas
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• v.19 no.4
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• pp.22-28
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• 2015

In order to keep the competitiveness of LPG fuel for transportation fuel, the difference in fuel consumption with gasoline and cost for an aftertreatment system should be reduced with continuous development of technology for LPG engine. In the present study, spray-guided type direct injection combustion system, whose configuration is composed of direct injector in the vicinity of spark plug, was employed to realize stable lean combustion. A certain level of nitrogen oxides($NO_x$) emits due to a locally rich mixture regions in the stratified mixture. With the application of EGR system for the reduction of $NO_x$, 15% of $NO_x$ reduction was achieved whereas fuel consumption and hydrocarbon emission increased. By the application of EGR, the combustion speed reduced especially appeared at initial flame development period and peak heat release rates and increasing rates for heat release rate decreased as EGR rate increased due to the dilution effect of intake air.

• Clean Technology
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• v.13 no.2
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• pp.151-158
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• 2007

An experimental study to investigate the condensing heat transfer characteristics of small diameter horizontal double pipe heat exchangers with R-22 and R-410A was performed. Experimental facility was constructed to calculate and observe HTC(heat transfer coefficients), flow patterns and pressure drop. The main components include a liquid pump, an evaporator, a condenser(test section), a sight-glass, pressure taps and measurement apparatus. Two pipes of different diameters are tested; One 5.35 mm ID 0.5 mm thick, the other 3.36 mm ID 0.7 mm thick. The mass flow rate ranged from 200 to $500\;ks/m^2{\cdot}s$ and heating capacity were form 1.0 to 2.4 kW. The flow patterns of R-22 and R-410A were observed with a high speed camera through the sight-glass. The tests revealed that HTC of R-410A was higher than that of R-22 by maximum 5%. Annular pattern was observed for the most cases but stratified flow was also detected when x<0.2. The pressure drop in 3.36 mm ID pipe was higher than that of 5.35 mm by $30{\sim}50%$. Comparing with previous correlations such as Shah, Fujii and Soliman's, Fujii' showed the best good agreement with my data with a maximum deviation of 40%.

• Korean Journal of Medicinal Crop Science
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• v.6 no.4
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• pp.258-264
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• 1998

This study was conducted to establish mass propagation system from seeds of Lavandula angustiolia Mill. Only 4% of dry seeds were germinated when they were incubated in $4^{\circ}C$. Germination rate of stratified seeds for 9 weeks was 15% higher in light than darkness. Soaking with 1000mg/l of $GA_3$ was helpful to overcome the effect of darkness. The optimal temperature for germination was $25^{\circ}C$ for the seeds that were treated with$GA_3$, solution. For the improvement of germination rates, pretreatment of $GA_3$ at 500-2000mg/l showed about 75% of germination, and in the combination treatment of $GA_3$, and BA, germination rate increased by about 10% in the treatment of 1000mg/l $GA_3+10mg/l$ BA compared with the 1000mg/l $GA_3$ treatment. Cold stratification treatment was very effective for seed germination, and over 70% of seeds were germinated when they were incubated in $4^{\circ}C$ for 9-12 weeks. In addition, there was synergic effect on the seed germination subject to stratification and 1000mg/l $GA_3$, treatment for 6 months. In the mixture of vermiculite: peatmoss (1 : 1, v/v), emergence rate was 6.7% in control and 65% in 1000mg/l $GA_3$ treatment, respectively.

• Journal of Korea Water Resources Association
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• v.56 no.2
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• pp.103-113
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• 2023

The river confluence is a section in which two rivers with different topographical and hyrodynamic characteristics are combined into one, and it is a section in which rapid flow, inflow of sediments, and hydrological topographic changes occur. In the confluence section, the flow of fluid occurs due to the difference in density due to the type of material or temperature difference, which is called a density flow. It is necessary to accurately measure and observe the confluence section including a certain section of the main stream and tributaries in order to understand the mixing behavior of the water body caused by the density difference. A comprehensive analysis of this water mixture can be obtained by obtaining flow field and flow rate information, but there is a limit to understanding the mixing of water bodies with different physical properties and water quality characteristics of rivers flowing with stratigraphic flow. Therefore, this study attempts to grasp the density flow through the water temperature distribution in the confluence section. Among the extensive data of the river, vertical data and water surface data were acquired, and through this, the stratification phenomenon of the confluence was to be confirmed. It was intended to analyze the mixed pattern of the confluence by analyzing the water mixing pattern according to the water temperature difference using the vertical data obtained by measuring the repair volume by installing the ADCP on the side of the boat and measuring the real-time concentration using YSI. This study can supplement the analysis results of the existing water quality measurement in two dimensions. Based on the comparative analysis, it will be used to investigate the current status of stratified sections in the water layer and identify the mixing characteristics of the downstream section of the river.