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Park, Sungwook,An, Mai Ngoc,Almeida, Guilherme,Palazon, Francisco,Spirito, Davide,Krahne, Roman,Dang, Zhiya,De Trizio, Luca,Manna, Liberato The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.40
<P>We developed a facile synthesis of nanocomposite powders of CsPbX3 nanocrystals (NCs) embedded in silica. The synthesis starts from colloidal Cs4PbX6 NCs that are mixed with tetraethyl orthosilicate in the presence of nitric acid, which triggers the sol-gel reaction yielding the formation of SiOx and the conversion of starting NCs into CsPbX3 ones. The overall reaction delivers CsPbX3 NCs encased in a silica matrix. The resulting CsPbX3/SiOx nano-composite powders exhibited enhanced moisture and thermal stability in air. Also, when mixing different CsPbX3/SiOx samples having diverse anion compositions, no interparticle anion exchange processes were observed, which is a further indication that the silica matrix acts as a robust barrier surrounding the NCs. Finallly, we used these composites as down-converter phosphors on top of a blue light-emitting diode (LED), delivering nearly ideal white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates (0.32, 0.33).</P>
Park, Su Han,Cha, Junepyo,Park, Sungwook,Lee, Chang Sik SAGE Publications 2012 Proceedings of the Institution of Mechanical Engin Vol.226 No.8
<P>The purpose of this study was to investigate the effect of the exhaust gas recirculation rate on the combustion and exhaust emission reduction characteristics of dimethyl ether fuel in a single-cylinder diesel engine. To investigate the effects on emission reduction, the test set-up was composed of a dimethyl ether supply system, a spray visualization system, an engine combustion system and an emissions analysis system. In this work, the spray visualization and exhaust emissions were measured using a high-speed camera with a metal halide lamp, a smoke meter and an emission gas analyser. The spray tip penetration and tip velocity of dimethyl ether fuel were lower than those of conventional diesel fuel. The reduction slope of the spray cone angle for dimethyl ether was less than that for diesel fuel owing to its low density and superior evaporation characteristics. The increase in the exhaust gas recirculation rate caused an extension of the ignition delay for dimethyl ether. During the extended ignition delay, the improved mixing characteristics influenced the slight decrease in the combustion period. An increase in the exhaust gas recirculation rate caused a significant reduction in the emission of nitrogen oxides. In addition, the soot emission was very low owing to the intrinsic characteristics of dimethyl ether (no direct carbon-carbon bonds). At the given equivalence ratio condition, the indicated specific hydrocarbon and indicated specific carbon monoxide emissions for dimethyl ether were extremely low when dimethyl ether spray was injected into the piston bowl (from 25 degrees before top dead centre to top dead centre). Also, in this case, a change in the exhaust gas recirculation rate for dimethyl ether combustion had minimal effects on the indicated specific hydrocarbon and indicated specific carbon monoxide emissions. These results suggest that the use of high exhaust gas recirculation with dimethyl ether fuel can achieve near-zero exhaust emissions (nitrogen oxides, soot, hydrocarbons and carbon monoxide).</P>
Park, Junkyu,Kim, Taehoon,Kim, Donghwan,Park, Sungwook Elsevier 2018 Fuel processing technology Vol.179 No.-
<P><B>Abstract</B></P> <P>This study was performed to analyze the wall impingement and fuel film formation in a DISI engine with injection strategies using image-based analysis and CFD. The direct injection engine uses a high-pressure injection strategy to improve the homogeneity of the air-fuel mixture, so the spray behavior was analyzed by spray visualization for various injection pressures, and the wall impingement was predicted for various engine operating conditions based on the acquired images. The mass distribution of the injected fuel was calculated using the injection profiles and the spray image, and the amount of fuel that impinges on the piston and wall (i.e., the geometric boundaries of the cylinder) was calculated using data from the spray behavior for various engine operation conditions such as load and engine speed. The image-based analysis was limited to understanding the influence of the injection strategy on the droplet behavior after wall impingement of the fuel spray. Therefore, CFD using KIVA 3 V code was additionally conducted to analyze the effects of the injection strategies on wall film formation and droplet rebounding reflecting in-cylinder conditions. In the early- and late-injection conditions, the initial piston position is high, and most of the injected fuel impinges on the piston. As the injection pressure increases, the injection timing at which wall impingement occurs is advanced because of the rapid spray development. The results of the 3D analysis for the temperature and the intake flow in the engine cylinder showed that both the wall impingement and the fuel film were reduced as the injection pressure increased because the fuel evaporation increased due to improved atomization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A prediction method of wall impingement in DISI engines is introduced. </LI> <LI> Effects of injection pressure and injection timing on spray wall impingement are analyzed using image-based method. </LI> <LI> 3D CFD are used to analyze effects of the engine conditions on formation of fuel film. </LI> <LI> Higher injection pressure conditions can reduce formation of fuel film due to superior vaporization characteristics. </LI> </UL> </P>
Junkyu Park,Donghwan Kim,Sungwook Park 한국자동차공학회 2020 International journal of automotive technology Vol.21 No.3
This study was performed to investigate the effects of L/D ratio of the nozzle on initial development and macroscopic spray behavior of diesel spray to understand the formation process of spray cone angle. Near-field and far-field spray visualization was performed for various injection pressures, and the effects of L/D ratio of the nozzle on spray cone angle were analyzed. A long-distance microscope and a CCD camera were used to obtain near-field spray images. Also, macroscopic spray development was evaluated using a high-speed camera and two metal halide lamps to compare the spray cone angle depending on L/D ratio. In the initial stage of injection, a laminar flow regime is observed, and downstream of the liquid column is deformed due to the large drag force of the surrounding gas. The area of the initial spray head, which has a small amount of momentum, becomes wider due to drag, and a strong eddy flow is formed around the deformed spray head. As the momentum of the supplied fuel increases over time, a mushroom-like structure is formed because momentum is continuously supplied at the center of the spray, while the outside of the spray head receives only drag force without providing additional momentum.
Front End Carrier의 상부 구조에 따른 강성 비교 연구
박성욱(Sungwook Park),공태윤(Taeyun Kong),김재용(Jaeyong Kim),소원섭(Wonsub So) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
Front End Module is assembled to the front area of the vehicle. In the case of front crash, the Front End Module should be able to absorb the impact and the deformation of Front End Module should be minimized. If the vehicle’s hood deformed by crash is opened, it can make the wind shield of vehicle broken and injure passengers. Because deformed and opened hood can cause the additional accidents, the stiffness supporting hood is very important. The stiffness of all developed vehicles must be verified in the development stage through Hood Latch Retention Test. And the test must be controlled strongly. The stiffness supporting hood & latch has the relationship with the Front End Carrier’s upper structure. The Higher inertia of Upper Section is advantageous, but the upper section can not be secured often because of vehicle’s styling or engine room layout or limitation of cost & weight , ETC, and these factor is different according to the vehicles We have developed several vehicle’s Front End Module since 1999 and we will introduce some kinds of knowhow from the development history of 2 vehicle’ Front End Module.