• 한국분무공학회지
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• 제9권2호
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• pp.9-17
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• 2004

The performance characteristics of lean burn system in gasoline engine are mainly affected by the air-fuel mixture in cylinder, gas exchange process of manifold system, exhaust emission of engine, and the electronic engine control system. In order to obtain the effect of performance factors on the optimum conditions of lean burn engine, this study deal with the behavior of mixture formation, gas flow characteristics of air, flow and evaporation analysis of spray droplet in cylinder, vaporization and burning characteristics of lean mixture in the engine, and the control performance of electronic engine control system. The optimum flow conditions were investigated with the swirl and tumble flows in the combustion chamber with swirl control valve. The performance characteristics and optimum condition of flow field in intake system were analyzed by the investigation of inlet flow of air and combustion stabilization on cylinder.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.99-105
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• 2007

It is very important to clarify the 3-D angular flow characteristics of in-cylinder bulk motion in the developing process of variable induction system. In-cylinder flow induced by variable induction system is very complex, so we can not describe the in-cylinder bulk flow characteristics using the conventional swirl or tumble coefficient. In this study, we introduced the new 3-D angular flow index, angular flow coefficient($N_B$), for in-cylinder bulk flow characteristics. And also, to confirm the index, we carried out the steady flow rig test for intake port of test engine varying valve lift on the test matrix.

• Journal of Mechanical Science and Technology
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• 제16권7호
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• pp.986-998
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• 2002

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of DI (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70° and 90°. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

• Korean Chemical Engineering Research
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• 제50권4호
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• pp.743-748
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• 2012

본 논문에서는 미세 환경이 Pseudomonas aeruginosa의 운동성에 주는 영향을 조사하기 위하여 다양한 크기의 미세유로 내에서 박테리아의 운동성을 분석하였다. 본 논문에서는 미세유체 칩을 사용하여 2차원 공간을 만들며, $10{\sim}100{\mu}m$ 너비의 채널 안에서 단일 박테리아의 운동 변수인 이동속도, 'run'운동 지속시간, 'tumble' 각도를 측정하였고 각 미세유로 내에서 박테리아의 운동을 표현할 수 있는 물리적 상수인 random motility coefficient를 구하였다. 상기의 물리적 측정치를 분석한 결과, 박테리아는 공간제약이 있는 경우 편모의 운동이 채널의 벽의 영향으로 인하여 회전 운동에 영향을 받게 되고, 'run' 운동 지속 시간이 짧아지는 것을 확인하였다. 따라서, 공간의 제한이 박테리아의 운동성을 감소시킴을 알 수 있었다. 본 연구의 결과는 박테리아의 운동성을 쉽고 정확하게 분석할 수 있는 측정 방법으로 널리 활용될 것으로 기대된다.

• 한국의류학회지
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• 제41권3호
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• pp.458-467
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• 2017

There is increased interest in clothes dryers and garments made of spandex-blend woven fabrics; however, there is limited information available for the laundering and drying these clothes. This study investigates the effects of washing and drying on shrinkage, skewness, and wrinkle for woven fabrics with and without spandex. When spandex with good elastic recovery was blended, the deformed shape from washing and drying improved skewness and wrinkle by easily returning to its original shape. However, these properties had a negative effect on shrinkage in terms of length and area change. When the influence of clothes maintenance was classified, the drying process had the biggest influence of 58%, followed by spinning-rinsingwashing. Tumble drying, in which the fabric is exposed to mechanical force and heat for a long period, had more negative effects on the dimensional stability than line drying. The spandex blend had the effect of preventing skewness and wrinkle in garments, but it was also shown to accelerate shrinkage by garment maintenance cycles. It was important to control drying in order to reduce shrinkage during the maintenance process; consequently, this had the greatest influence on the dimensional stability of fabrics. Therefore, line drying was more advantageous for spandex-blend fabrics than tumble drying in terms of management for shrinkage, skewness, and wrinkle.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1457-1469
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• 2002

This paper is the first of several companion papers, which investigate axial stratification process and its effects in an Sl engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it Is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swir and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the AFR at the spark plug and LML are very closely related and the AFR is the results of bulk air motion.

• 한국자동차공학회논문집
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• 제4권6호
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• pp.11-17
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• 1996

Many researches on natural gas engines, with lean mixtures are being conducted for the purpose of preservation of global environment. Lean combustion is one of the most promising method for increasing engine efficiency and reducing the emission from SI engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate, by use of swirl or tumble flow, are needed to guarantee a successful subsequent combustion. Experimental data were obtained on a 4-stroke, natural gas fueled SI engine to investigate the effect of compression ratio, swirl and spark plug electrode rotation on efficiency and emission under lean burn condition. Experimental results have displayed that higher compression ratio, presence of swirl vane and favorable direction of electrode gap brougth about the improvements in engine efficiency and its operational stability.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.37-44
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• 1998

Lean burn combustion is an important concept for improving the fuel consumption and exhaust emissions. However, the lean burning is associated with increased cycle-to-cycle combustion variations due to the ignition instabilities and redu- ced flame propagation rates. Engine stability under lean mixture conditions could be improved by increasing flame speed through enhanced flow characteristics and by securing ignitability with improvement of ignition systems. The effects of flow motion and ignition characteristics on the combustion performances were investigated in a 4-valve SI engine. Flow motions of tumble-swirl were varied with a swirl control valve attached at the inlet ports, while ignition energy and its distribution were controlled in a high -frequency ignition system by changing spark duration and spark frequency. The improvement of lean burn performance by the optimum flow motion and ignition characteristics is discussed.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.191-198
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• 1998

In this study, the effects of water vapor in inlet air, spark advance and fuel type in the spark ignition engine were investigated through the experiments of combustion and flame arriving pattern analysis using ionization probe. The results of flame propagation experiment using ionization probe show that the flame which ignited from spark plug located at the center of the combustion chamber propagated faster in exhaust side than in intake side due to the mixture flow motion inducted into combustion chamber from intake tumble port at all conditions. And as the partial vapor pressure increased, the flame propagation became slower in all direction. Especially effects were greater for intake side than the exhaust side.

• 한국정밀공학회지
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• 제28권1호
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• pp.56-62
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• 2011

Terrain recognition ability is crucial to the performance of legged robots in an outdoor environment. For instance, a robot will not easily walk and it will tumble or deviate from its path if there is no information on whether the walking surface is flat, rugged, tough, and slippery. In this study, the ground surface recognition ability of robots is discussed, and to enable walking robots to recognize the surface state and changes, a central moment method was used. The values of the sensor signals (load cell) of robots while walking were detected in the supported section and were analyzed according to signal variance, skewness, and kurtosis. Based on the results of such analysis, the surface state was detected and classified.