• 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.

• 대한기계학회논문집B
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• 제26권4호
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• pp.614-621
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• 2002

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure was 5.1MPa. Two dimensional spray fluorescence image of vapor phase was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC 90$^{\circ}$, 80$^{\circ}$, 70$^{\circ}$, and 60$^{\circ}$. With a fuel injection timing of BTDC 90$^{\circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC 60$^{\circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.915-920
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• 2001

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B, and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure is 5.1MPa. Two dimensional spray fluorescence image of vapor phases was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC $90^{\circ},\;80^{\circ},\;70^{\circ},\;and\;60^{\circ}$. With a fuel injection timing of BTDC $90^{\circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC $60^{\circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.

• 한국자동차공학회논문집
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• 제1권1호
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• pp.1-13
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• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• 대한기계학회논문집
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• 제18권4호
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• pp.920-932
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• 1994

The combustion phenomena of a reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design, because the flame speed is mainly determined by the turbulence at compression(TDC) process in S.I. engine. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. This paper describes cycle resolved LDV measurement of turbulent flow inside the cylinder of a 4-valve engine under motoring(non-firing) conditions, and studies the effect of intake port configurations on the turbulence characteristics using following parameters ; Eulerian temporal autocorrelation coefficient, turbulence energy spectral density function, Taylor micro time scale, integral time scale, and integral length scale.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.992-997
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• 2003

The flow characteristics along a intake/compression process are very important for the combustion process. The intake/compression flow fields are related to the piston shape of engine. The flow fields are analysed by using the ICEM-CFD IC3M code for the rapid mesh-generation and by using the STAR-CD code for the calculations. The influences of the piston bowl shapes were investigated. The results showed that piston shapes had influences on a intake/compression flow and offered the definite basic data in a design side.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.1-8
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• 2002

The flow and combustion patterns have been investigated inside the gasoline engine cylinder with the swirl or tumble flow, whereas the air flow characteristics, which are generated in the part of intake system before entering into the intake manifold, have not been known completely. It is necessary to analyze the flow field in the intake system consisting of air rater, throttle valve and intake manifold. The throttle valve, used to control the intake air flow rate, is important because it makes various mass flow rate and flow patterns. Three-dimen-sional How characteristics such as velocities, turbulent intensities and Reynolds shear stresses are measured by the hot wire anemometer at the exit of the throttle valve with the variation in the valve opening angle($15^{\circ}$, $45^{\circ}$, $75^{\circ}$ and $90^{\circ}$) and the Reynolds numbers (45000, 70000 and 140000). There are a lot of changes in flow characteristics at $75^{\circ}$ due to the large recirculation flow comparing with those of the other cases, and the streamwise velocity is especially enforced strongly below the valve shaft. The other component velocities are relatively large near the centerline parallel to the valve shaft. The effects of the Reynolds number on the flow field are not severe.

• 대한기계학회논문집B
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• 제32권11호
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• pp.878-883
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• 2008

The spray characteristics of a high pressure 6-hole injector were examined in a single cylinder optical direct injection spark ignition (DISI) engine. The effects of injection timing, in-cylinder charge motion, fuel injection pressure and coolant temperature were investigated using the 2-dimensional Mie scattering technique. It was confirmed that the in-cylinder charge motion played a major role in the fuel spray distribution during the induction stroke while the propagation of fuel spray was restrained during the compression stroke by the increasing pressure and the upward moving piston. In additions, it was confirmed that the liquid fuel droplets existing at the sprays edges were vaporized by the increase of the coolant temperature.

• 동력기계공학회지
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• 제11권4호
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• pp.5-11
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• 2007

본 연구는 SI기관 실린더 내의 유동장 변이 과정을 3차원 LDV 측정 기술을 사용하여 흡입과 압축과정 동안 정량적으로 분석하였다. 실험은 헤드에 각각 2개의 흡입밸브와 배기밸브를 갖는 기관이 모터링되는 공회전 상태에서 실시하였다. 지난 30년 동안 텀블과 스월은 실린더 내의 평균 유동 정량화에, 난류운동에너지는 난류 측정에 많이 사용되어 왔다. 그러나 텀블은 solid body 회전 유동을 비교하는데 적절하며, 서로 다른 유동 패턴 비교에는 부적절 하다는 것이 보고되고 있는 실정이다. 3차원 LDV시스템의 우수한 공간 분석 능력은 순간적인 유동장구조와 더불어 상대적으로 미세한 유동장의 구조 까지도 측정이 가능 하도록 하였다. 따라서 측정한 결과로부터 유동장의 난류운동에너지 등가면을 계산할 수 있었다. 본 실험 결과는 실린더 내의 난류 유동장 특성을 난류운동 에너지 등가면 정보를 이용하여 세심하게 관찰할 수 있음을 제시하고 있다.

• 한국분무공학회지
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• 제22권1호
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• pp.29-35
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• 2017

This paper describes the effects of spray breakup model constants on spray and combustion characteristics in single cylinder compression engine. KIVA-3V code coupled with a CHEMKIN chemistry solver was used for numerical analysis. In this study, spray simulations and combustion simulations are studied simultaneously. Spray simulation was conducted in constant volume to reduce the effects of air-flow as swirl or tumble. The model validation was conducted and there are little difference between experiments and simulation, this differences were reasonable. In spray simulation, the effects of model constants on spray tip penetration, spray patter and SMD were studied. Furthermore, the analysis of effects of breakup variables on combustion and emissions characteristics was conducted. The results show the KH-RT breakup model constants affects spray and combustion characteristics strongly. Increasing KH model variable (B1) and RT model constants ($C_{\tau}$, $C_{RT}$) induced slower breakup time.