• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.221-228
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• 2013

An experimental study was carried out to investigate the effects of the injection timing on the spray and combustion characteristics in a spray-guided direct-injection spark-ignition (DISI) engine under lean stratified operation. An in-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were employed in this study. The combustion in a stratified DISI engine was found to have both lean premixed and diffusion controlled flame combustion characteristics. The injection timing condition corresponding to the stratified mixture characteristics was verified to be a dominant factor for these flame characteristics. For the early injection timing, a non-luminous blue flame and low combustion efficiency were observed as a result of the lean homogeneous mixture formation. On the other hand, a luminous sooting flame was shown at the late injection timing because of an under-mixed mixture formation. In addition, the smoke emission and incomplete combustion products were increased at the late injection timing as a result of the increased locally rich area. On the other hand, the NOx emissions decreased and IMEP increased as the injection timing retarded. The combustion phasing produced by the injection timing was verified as the reason for this observation.

• 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.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.179-184
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• 1999

A Timing Diagram is almost used to represent the various signals such as an address bus, a data bus, and the control signals during design and analysis of a digital system. But if so, its representation is somewhat complicated and also it is difficult to analyze the operation of the system. In this paper, we proposed the representation method of timing diagrams with the EMFG(Extended Mark Flow Graph). In the EMFG representation of the system operation, the logical states due to the various signals of the system is graphically represented. Therefore the proposal method allows that it is easy to design as well as analyze the system. As examples applied, we represented the memory read cycle of $\mu$PD70320 CPU and the read cycle of MCM60256A memory with the EMFG.

• Journal of Energy Engineering
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• v.26 no.2
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• pp.32-38
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• 2017

The common rail diesel engine used in this study uses mechanically driven camshaft for the operation of intake and exhaust valves, and the timing of valve opening and closing is fixed according to the operating conditions of the vehicle. However, the electric generator engine operates at a constant speed and partial load. Therefore, in order to optimize the design of common rail diesel engine for power generation, the characteristics of diesel combustion and emissions according to the change of valve timing were examined and calculated in terms of fuel economy. The valve timing of the diesel engine influenced the combustion characteristics by changing the intake and exhaust flow and it was considered that the fuel efficiency of the generator could be improved.

• Journal of Advanced Navigation Technology
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• v.13 no.3
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• pp.337-343
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• 2009

In this paper, we proposed a burst mode symbol timing recovery unit that is applicable to the VDL Mode-2 using D8PSK modulation. A method that IIR loop filter is used to minimize symbol timing error is hard to apply to burst mode because its convergence time is long. That is, the fast convergence property is important. In this paper, the proposed method takes one sample which has maximum symbol power after the initial synchronization has been achieved by using preambles. The main principle of operation is that the unit moves one sample clock to advance or retard according to symbol power. We verify that the proposed method is operated well in ${\pm}100$ ppm or greater through the test results between Australia ADS Corp. transmitter and the designed receiver.

• Journal of ILASS-Korea
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• v.15 no.1
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• pp.1-7
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• 2010

As world attention has focused on global warming and air pollution, high efficiency diesel engines with low $CO_2$ emissions have become more attractive. Premixed diesel engines in particular have the potential to achieve the more homogeneous mixture in the cylinder which results in lower NOx and soot emission. Early studies have shown that the operation conditions such as the EGR, intake conditions, injection conditions and compression ratio are important to reduce emissions in a PCCI (Premixed Charge Compression Ignition) engine. In this study a modified cam was employed to reduce the effective compression ratio. While opening timing of the intake valve was fixed, closing timing of the intake valve was retarded $30^{\circ}$. Although Atkinson cycle with the retarded cam leads to a low in-cylinder pressure in the compression stroke, the engine work can still be increased by advanced injection timing. On that account, we investigated the effects of various injection parameters to reduce emission and fuel consumption; as a result, lower NOx emission levels and almost same levels of fuel consumption and PM compared with those of conventional diesel engine cam timing could be achieved with the LIVC system.

• International Journal of Automotive Technology
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• v.8 no.5
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• pp.555-562
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• 2007

The Variable Valve Timing(VVT) system for high performance is a key technology used in newly developed engines. The system realizes higher torque, better fuel economy, and lower emissions by allowing an additional degree of freedom in valve timing during engine operation. In this study, a model-based control method is proposed to enable a fast and precise VVT control system that is robust with respect to manufacturing tolerances and aging. The VVT system is modeled by a third-order nonlinear state equation intended to account for nonlinearities of the system. Based on the model, a controller is designed for position control of the VVT system. The sliding mode theory is applied to controller design to overcome model uncertainties and unknown disturbances. The experimental results suggest that the proposed sliding mode controller is capable of improving tracking performance. In addition, the sliding mode controller is robust to battery voltage disturbance.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.1
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• pp.19-29
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• 2019

This paper analyzes the design factors for GNSS anti-jamming receiver system in which the adaptive beamforming algorithm is applied in GNSS receiver system. The design analysis factors used in this paper are divided into three: antenna, beamforming algorithm, and operation environment. This paper analyzes the above three factors and presents numerical simulation results on antenna and beamforming algorithm.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.10 no.4
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• pp.135-142
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• 2011

This paper proposes a performance evaluation method for power consumption of set-top box (STB) stand-by mode transition schemes. A stand-by mode transition scheme characterizes the timing of mode transition. The timing of mode transition affects the duration of stand-by mode operation, and the power consumptions of STB as well. Recently a fast stand-by mode transition scheme (FMT) has been proposed based on user input for selecting the device to be connected to TV. In this paper, we evaluate power consumption of FMT and a conventional mode transition scheme. For the computation of the duration of stand-by mode operation, the user input events are modeled as Poisson process. Simulation results based on the modeling reveals that the proposed scheme is more effective in power saving than the conventional scheme by up to 30%.

• Journal of Positioning, Navigation, and Timing
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• v.6 no.1
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• pp.9-15
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• 2017

In this paper, results of a jammer detection and localization system operation are given. The system consists of receiver stations, a central tracking station, and a monitoring station and it was developed by our institute in 2014. Through real-time tests, it is confirmed that the developed system has an ability to estimate the location of interference sources with an accuracy of 50 m (CEP) even they was 10 km away. After verification, this system was installed in Incheon International Airport and operating results are being monitored by the airport and our institute continuously. In this year, there were some events that jamming signals were received from North Korea, so the data were analyzed and given here.