• 에너지공학
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• 제14권4호
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• pp.226-231
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• 2005

Essentially combination of spark ignition and compression ignition engines, the HCCI engine exhibits low NOx and Particulate Matter (PM) emissions as well as high efficiency under part load. This paper is concerned with the Homogeneous Charge Compression Ignition (HCCI) engine as a new concept in engines and a power source for future automotive applications. In this research, a 4 cylinder diesel engine was converted into a HCCI engine, and propane was used as the fuel. The purpose of this research is to show the effects of fuel flow rate and the temperature of the intake manifold on the performance and exhaust of an HCCI engine.

• International Journal of Automotive Technology
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• 제5권3호
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• pp.195-200
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• 2004

This paper is concerned with the Homogeneous Charge Compression Ignition (HCCI) engine as a new concept in engines and a power source for future automotive applications. Essentially a combination of spark ignition and compression ignition engines, the HCCI engine exhibits low NOx and Particulate Matter (PM) emissions as well as high efficiency under part load. The objective of this research is to determine the effects of Exhaust Gas Recirculation (EGR) rate on the combustion processes of HCCI. For this purpose, a 4-cylinder, compression ignition engine was converted into a HCCI engine, and a heating device was installed to raise the temperature of the intake air and also to make it more consistent. In addition, a pressure sensor was inserted into each of the cylinders to investigate the differences in characteristics among the cylinders.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 춘계종합학술대회
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• pp.392-397
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• 2000

Interlace된 2차원 필드영상에 대해 병렬로 DWT를 적용하는 압축기법을 제시하였다. 그 결과 영상의 분해 및 압축율의 증가와 화상 재구성의 PSNR을 증가시키며 신호압축 처리 시간을 단축시킨다. PSNR은 2의 멱수 N의 증가에 따라 지수함수로 감소한다. DCT 기반 압축보다 이득이 30%정도 높다. 독립된 병렬처리는 초당 처리능력을 향상시키며 프레임간 압축보다 간단하다. 또한 필드 영상에서 프레임을 근사 시킬 수 있다.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.9-14
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• 2002

A homogeneous premixed charge compression ignition engine has been experimentally studied far the reduction exhaust emissions of diesel engines. In this study, the gasoline fuel is injected into the intake manifold to from homogeneous pre-mixture in the combustion chamber and then this pre-mixture is ignited by small amount of diesel fuel directly injected into the cylinder. In the premixed charge compression ignition engine, NOx and smoke concentration of the exhaust emissions were reduced simultaneously as compared with the conventional diesel engine. The combustion characteristics of premixed charged diesel engine such as the power output, the rate of heat release, and the other characteristics are discussed.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.259-264
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• 2020

In this study, comparison study has been performed between two-stage compression and a vapor-recompression refrigeration cycle and a liquefaction using LNG cold heat. When using a first method using two-stage compression and a refrigeration cycle, at least three compressors are required, however when using LNG cold heat, no compressor is required since carbon dioxide can be pumped after condensing with the heat exchange with -160℃ of LNG. Through this study, we can save more than one hundred million KRW annually by using LNG cold heat instead of using gas compression and refrigeration cycle.

• Metals and materials international
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• 제24권6호
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• pp.1249-1255
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• 2018

High temperature compression tests for newly developed Al-Zn-Mg alloy were carried out to investigate its hot deformation behavior and obtain deformation processing maps. In the compression tests, cylindrical specimens were deformed at high temperatures ($300-500^{\circ}C$) and strain rates of 0.001-1/s. Using the true stress-true strain curves obtained from the compression tests, processing maps were constructed by evaluating the power dissipation efficiency map and flow instability map. The processing map can be divided into three areas according to the microstructures of the deformed specimens: instability area with flow localization, instability area with mixed grains, and stable area with homogeneous grains resulting from continuous dynamic recrystallization (CDRX). The results suggest that the optimal processing conditions for the Al-Zn-Mg alloy are $450^{\circ}C$ and a strain rate of 0.001/s, having a stable area with homogeneous grains resulting from CDRX.

• 한국통신학회논문지
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• 제19권9호
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• pp.1793-1801
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• 1994

본 논문에서는 직렬 연결된 N-단 증폭기의 1dB 이득 억압점을 예측하기 위한 새로운 방법을 제안한다. 제안된 방법은 각 증폭기 제작사로부터 제공된 스칼라 데이터를 사용하여 각 증폭기의 입출력 전력 전달함수를 산출하고 이것을 각 증폭기의 입출력이 정합되었다는 가정하에 스칼라 형태로 곱함으로써 서브 시스템의 입출력 전력 전달 함수를 산출한다. 이렇게 구해진 전달 함수를 이용하여 역으로 서브 시스템의 1dB 이득 억압점을 예측할 수 있다. 제안된 방법은 스칼라 데이타의 수에 관계없이 사용할 수 있는 일반적인 방법이지만 본 논문에서는 2개의 스칼라 데이타(선형 전력 이득, 1dB 이득 억압점)와 3개의 스칼라 데이타(선형 전력 이득, 1dB와 0.5dB 이득 억압점)만을 사용할 경우에 대해서만 각각 분석된다. 제안된 방법의 유용성을 확인하기 위해 Ku-band에서 동작하는 두개의 표본 증폭기를 사용하여 기존의 방법과 제안된 방법에 의한 예측 결과와 실험에 의해 측정된 결과를 서로 비교하기 위해 함께 제시한다.

• 동력기계공학회지
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• 제19권6호
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• pp.82-88
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• 2015

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.637-646
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• 2021

The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell's thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.969-970
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• 2010