• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.274-284
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• 1995

The effect of turbulence and ignition energy on flame kernel growth in mathanol-air mixtures has been studied in a constant volume vessel. Experiments were made under different turbulent intensity conditions, ignition energy and over a range of equivalence ratio. Characteristics of turbulent flow were grasped by measurments of gas pressure and visualization of flame propagation. Flow velocity was measured by use of hot wire anemometer. A comparison of the effect of turbulence on ignition probability and flame kernel volume variation ratio is also presented.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.193-196
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• 2015

Combustion of low concentration VOC in inert gas around the flammability limit has been experimentally studied. Streams of nitrogen and propane mixture with various compositions and flow conditions were treated by a turbulent partially-premixed pilot flame. HC and CO contents in exhaust gas measured and the flow patterns were visualized. The results suggested that there exists an optimal mixture velocity range for efficient combustion treatment for each flow condition and composition of the mixture.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.135-140
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• 2006

The stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition has been studied experimentally. The objectives are to explain the phenomenon of a liftoff height decreasing as increasing fuel velocity and to reveal the mechanisms of flame stability Hydrogen was varied from 100 to 300 m/s and a coaxial air was fixed at 16 m/s with a coflow air less than 0.1 m/s. The technique of PIV and OH PLIF was used simultaneously with CCD and ICCD cameras. It was found that the liftoff height of the jet decreased with an increased fuel jet exit velocity. The leading edge at the flame base was moving along the stoichiometric line. Finally we confirmed that the stabilization of lifted hydrogen diffusion flames is related with a turbulent intensity, which means combustion is occurred where the local flow velocity is equal to the turbulent flame propagation velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.153-164
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• 1997

Flame oscillation phenomena in a co-flow diffusion flame was experimentally studied with periodic fuel supply using a solenoid valve. The degree of excitation was controlled by changing the volume flux of fuel passing through the valve. Flame oscillation frequencies were measured utilizing a photodiode, a spectrum analyzer, video and high speed movies. Laser planar visualization was employed to study the correlation between the flame oscillation and the toroidal vortices. Observed are three regimes of flame oscillation, where the oscillation frequencies are for the multiples of excitation, the excitation itself and the flame natural oscillation. Both periods of natural oscillation and of excitation induced oscillation exist over one cycle of the excitation in the frequency multiplied regime. It is considered as an effect of balancing the influence of buoyancy driven vortex with that of excitation induced vortex near the excitation rate of 0.2. Flame shapes are become monotonous as increasing the excitation frequency to the range of over two fold of the natural oscillation. The flame oscillation can be modulated to the frequency of either multiples of excitation or excitation itself under certain conditions. This implies that the flame oscillation could be modulated to avoid the resonance frequency of the combustor, and shows the possibility of active control of the flame oscillation.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.2
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• pp.259-266
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• 2009

An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1398-1407
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• 1992

The prediction of heat loss during laminar flame propagation was carried out by measurement of gas pressure and visualization of flame propagation in the constant volume combustion chamber. And to validate the prediction, the instantaneous temperature at wall of combustion chamber was also measured. Consequently, it was found that heat loss was increased according to increasing of maximum flame travel distance, but rate of heat loss for heat release during laminar flame propagation was nearly constant. And heat loss depends on heat transfer area which was contacted the wall by burned gas regardless to spark plug location.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.86-94
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• 1999

Measured shock wave effects were investigated by changing shock strength and position with particular emphasis on the stability limits of hydrogen-air jet flames. For this purpose, a supersonic nonpremixed, jet-like flame was stabilized along the axis of a Mach 2.5 wind tunnel, and wedges were mounted on the sidewall in order to interact oblique shock waves with the flame. This experiment was the first reacting flow experiment interacting with shock waves. Schilieren visualization pictures, wall static pressures, and flame stability limits were measured and compared to corresponding flames without shock-flame interaction. Substantial improvements in the flame stability limits were achieved by properly interacting the shock waves with the flameholding recirculation zone. The reason for the significant improvement in flame stability limits is believed to be the adverse pressure gradient caused by the shock, which can elongate the recirculation zone.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.97-99
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• 2002

Turbulent premixed flames were a subject of many researches for a number of decades. Especially, Borghi suggested a manificent diagram classifying turbulent combustion reasions and Lipatnikov and Chomiak modified this diagram. But this diagram has difficulties tn defining a flame thickness and velocity and measuring integral length scales In addition, recently experimental techniques are being developed, so we can accurately use PIV diagnostics measuring 2D velocity field instead of LDV and make good use of PLIF techniques for obtaining the flame information. In this study, according to developing techniques, suggest a new diagram replacing the existing Borghi diagram. Simultaneous PIV/OH PLIF measurements are used, which measure a shear strain rate and a location of flames, respectively. The shear strain rate represents turbulence and the OH signal indicates the flame information, but there is no geometric Information which is very important to flame quenching. Hence, to consider the geometric information, calculate fractal dimensions of the OH images. So the diagram suggested in this research has three axes which consist of strain rate, OH signal, and fractal dimension and can classify turbulent premixed flames.

• Journal of ILASS-Korea
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• v.4 no.4
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• pp.17-23
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• 1999

Recently, many researchers have been studied a D.I. diesel engine because of the exhaust gas restriction and fuel consumption performance. It is well known that the fuel injection characteristics are the key factors on the diesel combustion and exhaust emission. In this study, the fuel injection characteristics of 5-hole injector and the combustion characteristics are investigated with the amount of fuel by means of the visualization method and visualization D.I. diesel engine system. As the results of the experiments, the spray pattern of the fuel injection and the diffusion flame of a D.I. diesel engine are clarified. In addition, combustion phenomena with operation conditions such as engine speed and engine load are made clear.

• Journal of ILASS-Korea
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• v.24 no.3
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• pp.130-136
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• 2019

Spray visualization of a vaporizer fuel injection system of a micro turbo jet engine was experimentally studied. The fuel heating by combustion was simulated by the high pressure steam generator and combustor inlet air from the centrifugal compressor was simulated by compressed air stored in the high pressure air tank. Spray visualization was performed with single vaporizer, and then six vaporizers which are same number of micro turbojet engine were used. As a results, the spray characteristics of the vaporizer were understood with pressure difference of the combustor inlet air and the fuel supply pressure. Spray angles with three types of vaporizer configuration were measured. In the results, guide vane configuration has a wider spray angle than the straight tube and smooth curve tube with a swirler, so it is expected that the fuel will be effectively distributed inside the combustor flame tube.