• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.178-185
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• 2006

This paper investigates the steady-state combustion characteristics of the Homogeneous charge compression ignition(HCCI) engine with variable valve timing(VVT) and dimethyl ether(DME) direct injection, to find out its benefits in exhaust gas emissions. HCCI combustion is an attractive way to lower carbon dioxide($CO_2$), nitrogen oxides(NOx) emission and to allow higher fuel conversion efficiency. However, HCCI engine has inherent problem of narrow operating range at high load due to high in-cylinder peak pressure and consequent noise. To overcome this problem, the control of combustion start and heat release rate is required. It is difficult to control the start of combustion because HCCI combustion phase is closely linked to chemical reaction during a compression stroke. The combination of VVT and DME direct injection was chosen as the most promising strategy to control the HCCI combustion phase in this study. Regular gasoline was injected at intake port as main fuel, while small amount of DME was also injected directly into the cylinder as an ignition promoter for the control of ignition timing. Different intake valve timings were tested for combustion phase control. Regular gasoline was tested for HCCI operation and emission characteristics with various engine conditions. With HCCI operation, ignition delay and rapid burning angle were successfully controlled by the amount of internal EGR that was determined with VVT. For best IMEP and low HC emission, DME should be injected during early compression stroke. IMEP was mainly affected by the DME injection timing, and quantities of fuel DME and gasoline. HC emission was mainly affected by both the amount of gasoline and the DME injection timing. NOx emission was lower than conventional SI engine at gasoline lean region. However, NOx emission was similar to that in the conventional SI engine at gasoline rich region. CO emission was affected by the amount of gasoline and DME.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.88-96
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• 2008

Currently, due to the serious world-wide air pollution by substances emitted from vehicles, emission control is enforced more firmly and it is expected that the regulation requirements for emission will become more severe. A new concept combustion technology that can reduce the NOx and PM in relation to combustion is urgently required. This study used a split injection method at a 4 cylinder common-rail direct injection diesel engine in order to apply the partially premixed charge compression ignition combustion method without significantly altering engine specifications And it is investigated that the effects of the injection ratio and SCV(swirl control valve) to emission characteristics. From these tests, soot(g) and NOx(g) emission could be reduced to 40% and 92% compared to base engine performance at specified engine driving conditions(6 points with weight factors) according to application of split injection and SCV(swirl control valve).

• Journal of the Korean Society of Combustion
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• v.18 no.1
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• pp.27-33
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• 2013

Hydrogen-dimethy ether(DME) partially premixed compression ignition(PCCI) engine combustion was investigated in a single cylinder compression ignition engine. Hydrogen and DME were used as low carbon alternative fuels to reduce green house gases and pollutant. Hydrogen was injected at the intake manifold with an injection pressure of 0.5 MPa at fixed injection timing, $-210^{\circ}CA$ aTDC. DME was injected directly into the cylinder through the common-rail injection system at injection pressure of 30 MPa. DME inejction timing was varied to find the optimum PCCI combustion to reduce CO, HC and NOx emissions. When DME was injected early, CO and HC emissions were high while NOx emission was low. As the DME injection was retarded, the CO and HC emissions were decreased due to high combustion efficiency. NOx emissions were increased due to the high in-cylinder temperature. When DME were injected at $-30^{\circ}CA$ aTDC, reduction of HC, CO and NOx emissions was possible with high value of IMEP.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.90-90
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• 2012

The electron/hole injections in organic electronic devices have long been an issue due to the large energy level mismatches between electrode and organic layer. To utilize the organic materials in electronic devices, functional thin layers have been used, which reduce the electron/hole injection barrier from electrode to organic material. Typically, inorganic compounds and organic molecules are used as an electron and hole injection layer, respectively. Recently, CsN3 and 1,4,5,8,- naphthalene-tetracarboxylic-dianhydride (NTCDA) are reported as a potential electron and hole injection layers. CsN3 shows unique properties that it breaks into Cs and N and thus Cs can dope organic layer into n-type. On the other side, hole injection anode, NTCDA forms gap states with anode material. In this presentation, we show the electronic structure changes upon the insertion of CsN3 and NTCDA at proper interfaces to reduce the charge injection barriers. These barrier reductions are correlated with device characteristics.

• Journal of Power System Engineering
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• v.18 no.6
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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.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1494-1495
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• 2006

A complete finite element analysis method for discharge onset process, which is governed and coupled by charge transport equation and electric field equation, was presented. The charge transport equation of first order was transformed into a second-order one by utilizing the artificial diffusion scheme. The two second-order equations were analyzed by the finite element formulation which is well-developed for second-order ones. The Fowler-Nordheim injection boundary condition was adopted for charge transport equation. After verifying the numerical results by comparing to the analytic solutions using parallel plane electrodes with one carrier system, we extended the result to blade-plane electrodes in 2D xy geometry with three carriers system. Radius of the sharp tip was taken to be 50 ${\mu}m$. When this sharp geometry was solved by utilizing the space discretizing methods, the very sharp tip was found to cause a singularity in electric field and space charge distribution around the tip. To avoid these numerical difficulties in the FEM, finer meshes, a higher order shape function, and artificial diffusion scheme were employed.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1984-1985
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• 2007

Polyimide is widely used as a high-temperature insulating material. Space charge distributions in polyimide (PI) films strongly depend upon electric field, temperature, water content and so on. We observed space charge distributions in PI films with various water contents. When a dc field was applied to as-received PI films or water-treated PI films, positive and negative homo space charges were observed near the respective electrodes at 333 K. In dried PI films, the homo space charges were much reduced, and positive and negative hetero space charges in the bulk were clearly observed. The space charge amounts in water-treated PI films were smaller than in as-received ones, while the current density in water-treated PI film was larger than that in as-received one by two or more orders of magnitude. These suggest not only that the charge injection from the electrode is enhanced by absorbed water but also that absorbed water makes carriers mobile. The decay of space charge was also faster in water-treated PI than in as-received or dried one. This also supports the enhancement of apparent mobilities of carriers in PI by absorbed water.

• JSTS:Journal of Semiconductor Technology and Science
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• v.12 no.4
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• pp.467-472
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• 2012

In this paper, we present a finite element method (FEM) study on the space charge effects in organic light emitting diodes. The physical model covers all the key physical processes in OLEDs, namely charge injection, transport and recombination, exciton diffusion, transfer and decay as well as light coupling, and thin-film-optics. The exciton model includes generation, diffusion, and energy transfer as well as annihilation. We assumed that the light emission originates from oscillation which thus is embodied as exciton in a stack of multilayer. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution. We also report our investigation on the influence of the insertion of the emission layer (EML) in the bilayer structure.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.86-96
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• 2007

A direct-injection stratified-charge(DISC) engine has been considered as a promising alternative in spite of high unburned hydrocarbon emission levels during light load operation. In this paper investigation is made to characterize formation and combustion processes of stratified mixture charge in a simple constant volume combustion chamber. Both experimental and numerical analyses are performed for fluid and combustion characteristics with 3 different induction types for rich, homogeneous and lean mixture conditions. The commercial code FIRE is applied to the turbulent combustion process in terms of measured and calculated pressure traces and calculated distributions of mean temperature, OH radical and reaction rate. It turns out that the highest combustion rate occurs for the rich state condition at the spark ignition location due to existence of stoichiometric mixture and timing.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.328.1-328.1
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• 2014

MOSFET degradation의 대부분은 hot-carrier injection에 의한 interface state (Dit)의 생성에서 비롯되며 따라서 본 연구에서는 신뢰성에 대한 한 가지 방법으로 Charge pumping method를 이용하여 MOSFET의 interface trap(Dit)의 변화를 측정하였다. 소스와 드레인을 ground로 묶고 게이트에 펄스를 인가한 후 Icp를 측정하여 Dit를 추출하였다. 온도를 293~343 K까지 5 K씩 가변했을 때 293K의 Icp(${\mu}A$)는 0.12 nA 313 K는 0.112 nA 343 K는 0.926 nA이며 Dit (cm-1/eV-1)는 $1.61{\times}10^{12}$ (Cm-2/eV-1) $1.49{\times}10^{12}$ (Cm-2/eV-1) $1.23{\times}10^{12}$ (Cm-2/eV-1)이다. 측정결과 Dit는 Icp가 높은 지점에서 추출되며 온도가 높아지게 되면 Icp전류가 낮아지고 Dit가 줄어드는 것을 볼 수 있다. 온도가 올라가게 되면 carrier들이 trap 준위에서 conduction band 위쪽에 이동하게 되어서 interface에 trap되는 양이 작아지게 된다. 그래서 이때 Icp를 이용해 추출한 Dit 는 실제로 trap의 양이 줄어든 것이 아니라 Thermal excess 현상으로 인해 측정되는 Icp의 양이 줄어든 것으로 분석할 수 있다.