• 한국자동차공학회논문집
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• 제4권5호
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• pp.197-205
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• 1996

The flow characteristics of five different 4-valve cylinder heads were investigated in a steady flow rig using laser-Doppler velocimetry. The tumble flow of each head with pentroof combustion chamber was quantified by nondimensional tumble number using a tumble adaptor. The formation of tumbling vortex was examined in an optical single-cylinder engine which has windows for in-cylinder LDV measurements. Tumble vortex ratio was estimated from the tumble flow measurement. The four-valve cylinder heads with pent-roof combustion chamber showed the tumble vortex from the intake process, which was investigated in the steady flow test. The tumble adaptor which converts the tumble into swirl flow was found to be feasible in predicting the tumble flow in the real engine. The tumble strength in the steady flow test coincides with that in the real engine experiment within 15%. It was found that the steady flow test on the four-valve cylinder heads provides the tip for a better design of cylinder head.

• 한국자동차공학회논문집
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• 제8권6호
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• pp.51-59
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• 2000

In-cylinder spray flow motion plays an important in the adjustment of mixture preparation with a fundamental spray characteristics and in-cylinder flow field well in direct-injection gasoline engine. In this study, the fundamental spray characteristics such as mean drop size, velocity distribution, spray angle were measured and in-cylinder spray flow motion was visualized in order to optimize intake port, piston top land and combustion chamber shapes in the development stage of mass-produced G야 engine. For these experiments, the PDPA measurements and Mie scattering technique were used for detailed spray characteristics and in-cylinder spray motions were obtained by use of ICCD camera through the single-cylinder optical engine. From the experimental results, the test injector shows a good low-end linearity between the dynamic flow and fuel injection pulse width and the fuel spray of 20mm or less in SMD with good spray symmetry. In addition, the in-cylinder tumble flow has more effect on the homogeneous mixture formation than that of in-cylinder swirl flow at early injection mode and the in-cylinder swirl flow plays a better role of stratified mixture preparation than tumble flow at late injection mode.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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• pp.33-38
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• 2002

An optical single cylinder diesel engine equipped with a common-rail injection system has been built to investigate diesel combustion and emission characteristics. Three optical widows (piston crown quartz for bottom view of the cylinder, upper piston quartz for allowing laser sheet and liner quartz for side view) have been placed in the optical engine to visualize spray characteristics and combustion process inside the cylinder. Before doing further research using various optical diagnostics with the optical engine, fundamental combustion experiments and flame visualization incorporating a high speed motion analyser have been carried out with a wide range of engine operating conditions.

• 한국자동차공학회논문집
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• 제3권6호
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• pp.87-95
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• 1995

A commercial DOHC four valve engine was modified to make a single-cylinder optical model engine with replaceable head. Three kinds of head were used to generate swirl, tumble, and combined swirl/tumble motion. Schlieren visualization technique was applied to characterize the in-cylinder flow qualitatively. Particle Image velocimetry has been developed and applied for the quantitative flow measurements. Axial and tangential flow motion inside the cylinder has been characterized. The swirl/tumble port shows beneficial results in terms of turbulence generation for the initial flame propagation and mean swirl motion for the overall flame propagation.

• 한국자동차공학회논문집
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• 제8권5호
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• pp.96-104
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• 2000

It is well known that combustion stability under idle and part-load conditions directly affect fuel economy and exhaust emission. In practice, there have been a lot of studies so that a significant improvement in combustion stability has been achieved in this research field. However, applying published results to the development process of mass production engine, there are still many problems which are solved previously. In this study, initial flame behavior and flame propagation characteristic were investigated statistically in order to optimize combustion chamber shapes in the development stage of mass production S.I. engine. To the purpose, the authors applied the flame image capturing system to single cylinder optical engine. The captured flame images were effectively analyzed by using the image processing program which was developed by the authors and adopted new threshold algorithm instead of conventional histogram analysis. In addition, the cylinder pressure was also measured simultaneously to compare evaluated flame results with cylinder pressure data in terms of the combustion characteristics, combustion stability, and cycle-to-cycle combustion variability.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.9-17
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• 2001

This paper is the second of 3 companion papers which investigate axial stratification process. In-cylinder fuel behavior has been investigated in the port injected Sl engine by visualizing for the purpose of understanding stratification. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of the single cylinder optical engine and the Mie scattered light has been captured through the quartz window in the piston head with an ICCD camera. Fuel has been replaced with an air-ethanol mixture to utilize atomized fuel spray fur the visualization purposes. This results have been compared with steady flow concentration measurement. For low/medium swirl port, the early injection makes such a fuel distribution state that is upper-rich, middle-lean and lower-rich along the combustion chamber and cylinder by tumbling motion. On the other hand, the late injection induces upper-rich, middle-lean and lower-rich state due to the short fuel penetration.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.18-26
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• 2001

This paper is the third of 3 companion papers which investigate axial stratification process. In-cylinder fuel behavior has been investigated in the port injected SI engine by visualizing for the purpose of understanding stratification. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of the single cylinder optical engine and the Mie scattered light has been captured through the quartz window in the piston head with an ICCD camera. Fuel has been replaced with an air-ethanol mixture to utilize atomized fuel spray for the visualization purposes. This results have been compared with steady flow concentration measurement. In high swirl port, the most fuel remains at combustion chamber and upper cylinder region without being affected by injection timing. The macro-distributed state is not changed but the difference of the amount of fuel around the spark plug varies according to injection timing, which determines LML.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.19-27
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• 2001

This paper is the first of 3 companion papers which investigate axial stratification process. In-cylinder fuel behavior has been investigated in the port injected SI engine by visualization for the purpose of understanding stratification. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of the single cylinder optical engine and the Mie scattered light has been replaced with an air-ethanol mixture to utilize atomized fuel spray for the visualization purposes. This results have been compared with steady flow concentration measurement. For no swirl port, the axial penetration depends on the fuel injection timing. The fuel tends to remain in the upper region of the cylinder far from the spark plug and the distribution is not affected by the injection timing except 90 ATDC.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.23-32
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• 2002

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean bum operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean bum performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using an W intensified high-speed CCD camera. Concepts of flame area speed, In addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics. The results show the correlation between the flame propagation characteristics, which is related to engine performance of lean region, and engine design parameters such as swirl ratio, piston geometry and injection timing. Stronger swirl resulted in foster flame propagation under open valve injection. The flame speed was significantly affected by injection timing under open valve injection conditions; supposedly due to the charge stratification. Piston geometry affected flame propagation through squish effects.

• 대한기계학회논문집B
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• 제33권9호
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• pp.722-727
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• 2009

The effect of the intake flow on the spray structure of a high pressure 11-hole fuel injector were examined in a single cylinder optical direct injection spark ignition (DISI) engine. The effects of injection timing and in-cylinder charge motion were investigated using the 2-dimensional Mie scattering technique. It was confirmed that in the homogeneous charge mode, the in-cylinder swirl charge motion played a major role in the fuel spray distribution during the induction stroke rather than the tumble flow. But, in the stratified charge mode, the effect of the in-cylinder charge was not so large that the injected spray pattern was nearly maintained and the increase of in-cylinder pressure by the upward moving piston reduced the fuel spray penetration.