• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.65-73
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• 1996

Flame propagation in a four-valve spark-ignition optical engine was visualized under lean-bum conditions with A/F=18 at 2000rpm. The early flame development in a four-valve pentroof-chamber single-cylinder engine was examined with imaging of the laser-induced Mie scattered light using an image-intensified CCD camera. Flame profiles along the line-of-sight were also visualized through a quartz piston window. Two-dimensional flame structures were visualized with a Proxitronic HF-1 fast motion camera system by Mie scattering from titanium dioxide particles along a planar laser sheet generated by a copper vapor laser. The flame propagation images were subsequently analysed with an image processing programme to obtain information about the flame structure under different tumble flow conditions generated by sleeved and non-sleeved intake ports. This allowed enhancement of the flame images and calculation of the enflamed area, and the displacement of its center, as a function of the tumble flow induced by the pentroof-chamber in the vicinity of spark plug. Image processing of the early flame development quantified the correlation between flame and flow characteristics near the spark plug at the time of ignition which has been known to be one of the most important factors in cyclic combustion variations in lean-burn engines. The results were also compared with direct flame images obtained from the natural flame luminosity of the lean mixture.

• Journal of Power System Engineering
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• v.20 no.2
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• pp.32-42
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• 2016

Under part load condition of spark-ignition engine, pumping loss had great effect on engine efficiency. To reduce pumping loss, the study designed spark-ignited engines to make direct spray of gasoline to combustion chamber. In spark-ignited direct-injection engines, ignition probability is important for successful combustion and flame propagation characteristics are also different from pre-mixed combustion. This study designed a visualization testing device to study ignition probability of spark-ignited direct-injection LPG fuel and combustion flame characteristics. This visualization device consists of combustion chamber, fuel supply system, air supply system, electronic control system and data acquisition system. Ambient pressure, ambient temperature and ambient air flow velocity are important parameters on ignition probability of LPG-air mixture and flame propagation characteristics, and the study also found that sprayed LPG fuel can be directly ignited by spark-plug under proper ambient conditions. To all successful cases of ignition, the study recorded flame propagation image in digital method through ICCD camera and its flame propagation characteristics were analyzed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.2 s.257
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• pp.132-140
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• 2007

The temperature and soot of the visualized diesel engine's turbulent flow of the flame was measured qualitatively. In the combustion chamber, in order to judge the affect that the swirl current has on the current ratio two heads with different ratios were used. Using a high speed camera, the results were analyzed using flame visualization. In order to measure the temperature and soot of the turbulent flames like diesel flames, two color methods were used to acquire temperature and the soot of the flames according to the conditions through analyzing the two wavelengths of the flames. It was possible to measure the highest temperature of the non-swirl head visualized engine, which is approximately 2400K, and that swirl head engine managed up to 2100K. With respect to the visualized diesel engine soot, we got the grasp of the KL factor which bears the qualitative information of the soot. This study is dedicated to suggesting the possibility of measuring not only the temperature but also soot of the diffusion flame of the diesel engine turbulent flames.

• Journal of the Korean Society of Visualization
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• v.2 no.1
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• pp.8-11
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• 2004

Conditional sampling measurement is required for conditional averages as well as unconditional Favre averages to resolve different flame structures of turbulent combustion. A Favre average can be obtained as an integral of conditional average and Favre PDF in terms of the mixture fraction, which is a preferred choice as a sampling variable in diffusion controlled turbulent combustion. MILD combustion data are presented as an example for a conditionally averaged data set and comparison with CMC calculation results.

• Journal of the Korean Society of Combustion
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• v.4 no.1
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• pp.49-57
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• 1999

An experimental study on double-concentric diffusion flame has been carried out in order to investigate the shape, the flame length, and the other characteristics of the flame. Flow visualization of the flame by the $TiO_2$ particles and also the emission measurements are conducted. The commercial grade LP gases are used as fuel. The inverse diffusion flames are formed at the center when the central air flow rate is about 0.1 L/min. With a larger flow rate of the central air jet than 0.2 L/min the flame turns to be an annular-shaped flame, which is very bright. When the central air flow rate increases over 2.4 L/min, the flame turns to blue and the flame tips are opened because of the lifting of the inner part of the flame. Because of this lifting and the incomplete combustion, the CO emission increases abruptly from 25 ppm to more than 150 ppm. On the contrary, the NOx emission is decreased.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.19-24
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• 2010

Five different size of orifice were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The initial flame development and flame propagation were analyzed by the mass burned fraction and combustion enhancement rate. The combustion pressures were measured to calculate the mass burned fractions and the combustion enhancement rates. In addition, the flame propagations were visualized by the shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burned fraction were increased when using the torch-ignition device. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage.

• Journal of the Korean Society of Combustion
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• v.4 no.1
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• pp.39-47
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• 1999

A combustion flame visualization system, which is used as an engine diagnostics tool, was developed in order to understand the combustion reaction mechanism in the development stage for S.I. engines. The measurement system consists of an I-CCD camera and a computer-aided image processing system. By using optically accessible engine system, the flame structure was analyzed from the acquired graylevel image and the direction of flame propagation (shape of flame) has been measured to understand combustion phenomena. And combustion radical which involves combustion information were measured. As a result, strong relation between combustion radicals intensity ratio and air excess ratio was found.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.504-511
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• 2000

PIV(Particle Image Velocimetry) is a recently developed technique for visualizing the fluid velocity fields. Because it has several advantages over the LDV(Laser Doppler Velocimetry), it became one of the most popular diagnostic tools in spite of its short history. However, its application to combustion is restricted by some problems such as flame illumination, scattered light refraction, particle density variation due to heat release, the combined effect of abrupt change in particle density and fluid velocity on flame contour, and thermophoresis which is particle lagging due to temperature gradient. These problems are expected to be originated from the non-continuous characteristics of flames and the limitations of particle dynamics. In the present study, these problems were considered for the visualization of the instantaneous coaxial hydrogen diffusion flame. And the instantaneous flame contour was detected using particle density difference. The visualized diffusion flame velocity field shows its turbulent and meandering nature. It was also observed that the flame is located inside the outer shear layer and flame geometry is largely influenced by the vorticity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.275-285
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• 2003

A visualization study on the effect of forcing amplitude in tone-excited jet diffusion flames has been conducted. Visualization techniques are employed using optical schemes. which are a light scattering photography. Flame stability curve is attained according to Reynolds number and forcing amplitude at a fuel tube resonant frequency. Flame behavior is globally grouped into two from attached flame to blown-out flame according to forcing amplitude: one sticks the tradition flame behavior which has been observed in general jet diffusion flames and the other shows a variety of flame modes such as the flame of a feeble forcing amplitude where traditionally well-organized vortex motion evolves, a fat flame. an elongated flame. and an in-burning flame. Particular attention is focused on an elongation flame. which is associated with a turnabout phenomenon of vortex motion and on a reversal of the direction of vortex roll-up. It is found that the flame length with forcing amplitude is the direct outcome of the evolution process of the formed inner flow structure. Especially the negative part of the acoustic cycle under the influence of a strong negative pressure gradient causes the shapes of the fuel stem and fuel branch part and even the direction of vortex roll-up to dramatically change.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1652-1661
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• 2000

A visualization study using the schlieren method is adopted in an optically-accessible, cylindrical constant volume combustion chamber to identify the mechanism of ignition energy and ignition system interaction in spark ignited, lean gasoline-air mixture. In order to research the effects of ignition system on flame propagation, two kinds of ignition system are designed, and several kinds of spark plugs are tested and evaluated. To control the discharge energy, the dwell time is varied. The initial flame development is quantified in terms of 2-D images which provides information about the projected flame area and development velocity as a function of ignition system and discharge energy. The results show that high ignition energy and extended spark plug gap can shorten the combustion duration in lean mixtures. The material, diameter and configuration of electrodes the flame development by changing the transfer efficiency from electrical energy to chemical energy and discharge energy. However these factors do not affect of flame development as much a ignition energy or extended gap does.