• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1698-1703
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• 2004

To understand the high expansion effects by adopting intake closing time in the cases of compensating intake air-mass and effective compression ratio simultaneously, fundamental study was carried out by using RICEM realizing Atkinson cycle. Intake air-mass and effective compression ratio were compensated by increasing supercharged pressure and geometric compression ratio. The results showed that the increasing rates of expansion ratio and expansion-compression ratio were increased by compensating both a intake air-mass and effective compression ratio the same tendencies were obtained with the increases of compression ratio and cut off ratio It was also found that LIVC has more advantages in expansion ratio and effective work than those of EIVC under above conditions.

• 농업과학연구
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• 제37권3호
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• pp.501-508
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• 2010

A swirl chamber type diesel engine attachable to 18 kW agricultural tractors was improved to reduce exhaust emissions. Compression ratio and throat area ratio of the combustion chamber were varied to determine optimum combustion conditions. Tests were composed of full load and 8-mode emission tests. Compression ratio was fixed as 21, but the swirl chamber volume was increased by 3.8%. Output power, torque, specific fuel consumption, exhaust gas temperature, and smoke level were not considerably different for compression ratios of 21.5 (reference condition) and 21 (test condition), while NOx, HC, CO and PM levels for the compression ratio of 21 were decreased by 11%, 46%, 28%, 11%, respectively, from those for the compression ratio of 21.5. The tests were also conducted with a compression ratio of 22 and 4.3% increased chamber volume. Output power, torque, exhaust gas temperature and smoke level were greater, while specific fuel consumption was less for the compression ratio of 22 than those for the compression ratio of 21.5. Increase of compression ratio decreased HC and CO levels by 24%, 39%, but increased NOx and PM levels by 24%, 39%. Based on these results, a compression ratio of 21 was selected as an optimum value. Then, full load tests with the selected compression ratio of 21 were carried out for different throat ratios of 1.0%, 1.1%, 1.2%. Output power and torque were greatest and smoke was lowest when throat area ratio was 1.1%, which satisfied the target values of specific fuel consumption (less than 272 g/$kW{\cdot}h$) and exhaust gas temperature (less than $550^{\circ}C$). Therefore, a throat area ratio of 1.1% was selected as an optimum value.

• 한국자동차공학회논문집
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• 제13권4호
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• pp.145-151
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• 2005

Natural gas is one of clean fuels that can replace petroleum-based fuels, because it has low exhaust emission, comparatively high thermal efficiency and abundant deposits. In this addition, owing to high octane number and wide lean flammability limit, it has a strong point to increase the compression ratio. For this reason, the research is being actively executed to increase the generating power and thermal efficiency of the engine by raising the compression ratio through utilization of high octane number relevant to development of CNG engine. In this study, 0.63L single cylinder diesel engine has been used to alter easily compression ratio. Compression ratio has gotten under control by modifying the thickness of gasket between cylinder head and block without major structural modifications. As the result, as compression ratio has increased, generating power and fuel consumption ratio have been improved. As for emission concentration, as compression ratio has increased, THC concentration has been decreased while exhause concentration of NOx increased. In case compression ratio has excessively increased, brake output decrease and cycle variation have been increased. As the result acquired by analyzing brake output, fuel consumption ratio, cycle variation and exhaust, the engine driving condition has acquired $\varepsilon=13$ as the optimal compression ratio in this study.

• 에너지공학
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• 제24권3호
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• pp.61-66
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• 2015

Homogeneous charge compression ignition (HCCI) engine combines the combustion characteristics of a compression ignition engine and a spark ignition engine. HCCI engines take advantage of the high compression ratio and heat release rate and thus exhibit high efficiency found in compression ignition engines. In modern research, simulation has be come a powerful tool as it saves time and also economical when compared to experimental study. Engine simulation has been developed to predict the performance of a homogeneous charge compression ignition engine. The effects of compression ratio, cylinder pressure, rate of pressure rise, flame temperature, rate of heat release, and mass fraction burned were simulated. The simulation and analysis show several meaningful results. The objective of the present study is to develop a combustion characteristics model for a homogeneous charge compression ignition engine running with isooctane as a fuel and effect of compression ratio.

• 한국수소및신에너지학회논문집
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• 제23권6호
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• pp.628-633
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• 2012

It was found that the pure hydrogen-air pre-mixture was self-ignited at a high compression ratio without any assisting method in room temperature, thus refuting the preconception that compression ignition of hydrogen engine was impossible. Therefore, in order to analyze the correlation of compression ignition condition at cold start with hydrogen HCCI engine clearly, the possibility of compression igniting compression ratio is investigated with the change of equivalence ratio and engine speed, experimentally. As the results, it is confirmed that the possibility of compression-igniting compression ratio at cold start was decreased by increasing equivalence ratio due to decreasing auto-ignition temperature. In addition, it is grasped that the possibility of compression-igniting compression ratio at cold start is decreased around 14.9% by increasing engine speed at same supply energy.

• International Journal of Automotive Technology
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• 제7권3호
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• pp.295-301
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• 2006

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV(Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss.

• 한국수소및신에너지학회논문집
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• 제4권1호
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• pp.1-9
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• 1993

To find performance and knock limit for compression ratio in hydrogen fueled engine, the variable compression ratio hydrogen fueled engine which was able to vary compression ratio during firing was manufactured and estimated. The characteristics of the variable compression ratio hydrogen fueled engine were as follows : 1) compression ratio variation by moving of cylinder head, 2) OHC which can be realized low S/V ratio, short flame propagation distance and unvariable configuration of combustion chamber for compression ratio variation, 3) direct injection of hydrogen gas to restrict back fire.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.106-112
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• 2013

Compression ratio is an important factor affecting engine performance and emission characteristics since thermal efficiency of spark ignition engine can be theoretically improved by increasing compression ratio. In order to evaluate the effect of compression ratio change in HCNG engine, natural gas engine was employed using HCNG30 (CNG 70 vol%, hydrogen 30 vol%). Combustion and emission characteristics of CNG and HCNG fuel was analyzed with respect to the change of compression ratio at each operating condition. The results showed that thermal efficiency improved and $CH_4$, $CO_2$ emission decreased with the increase in compression ratio while $NO_x$ emissions were decreased at a certain excess air ratio condition. Higher thermal efficiency and further reduction of exhaust emissions can be achieved by the increase of compression ratio and the retard of spark timing.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2150-2156
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• 2018

We suggest a systematic method for obtaining the optimal compression ratio in the multi-stage closed-loop compression process of carbon dioxide. Instead of adopting the compression ratio of 3 to 4 by convention, we propose a novel approach based on mathematical analysis and simulation. The mathematical analysis prescribes that the geometric mean is a better initial value than the existing empirical value in identifying the optimal compression ratio. In addition, the optimization problem considers the initial installation cost as well as the energy required for the operation. We find that it is best to use the fifth stage in the general closed-loop type carbon dioxide multi-stage compression process.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2009년도 IWAIT
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• pp.80-84
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• 2009

This paper investigates the relationship between the compression ratio and the gamut area for a reconstructed image when using JPEG and JPEG2000. Eighteen color samples from the Macbeth ColorChecker are initially used to analyze the relationship between the compression ratio and the color bleeding phenomenon, i.e. the hue and chroma shifts in the a*b* color plane. In addition, twelve natural color images, divided into two groups depending on four color attributes, are also used to investigate the relationship between the compression ratio and the variation in the gamut area. For each image group, the gamut area for the reconstructed image shows an overall tendency to increase when increasing the compression ratio, similar to the experimental results with the Macbeth ColorChecker samples. However, with a high compression ratio, the gamut area decreases due to the mixture of adjacent colors, resulting in more grey.