• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1007-1010
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• 2006

In order to optimize the rotating angle of the auto louver, the air-cleaner with turbo fan was numerical and experimentally analyzed . The noise generated from the auto louver was changed by modifying the installation angle of the louver. Flow field and flow noise were analyzed numerically by commercial tool SC/Tetra and FlowNoise S/W. Experiment was also done at anechoic chamber. From the numerical and experimental data, we can find the optimal rotating angle for auto louver of the air-cleaner.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.19-26
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• 2002

The objective of this study is to examine a DI(Direct Injection) gasoline spray development process under different ambient pressures using PIV(Particle Image Velocimetry). fuel spray experiments were performed within a constant volume chamber. The spray structure, velocity maps, velocity and vorticity contours were obtained to investigate its spray characteristics. It was found that higher ambient pressure has a significant effect on radial growth of the spray. The position which has a maximum velocity moved from the spray edge to the spray center as ambient pressure was increased. Higher ambient pressure moved a maximum vorticity position upward of the spray.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1013-1018
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• 2008

Vortex Inertial Staged Air (VIStA) burner for an once-through type boiler has been restored to the original premixed type to reduce nitrogen oxide (NOx) emission. The premixed version yields additional de-NOx effect by 20 ppm. The flame is formed closer to the wall at the 1st stage combustion chamber compared with the non-premixed one. The combustion characteristics are more sensitive to the air distribution for the premixed type, which necessitates proper optimization.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.413-418
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• 2012

A modified VIStA (Vortex Inertial Staged Air) burner has been developed and applied to a once-through type boiler. The secondary air is supplied through a swirler instead of nozzles, which stabilizes the flame and reduces carbon monoxide (CO) emissions. However, the modification increases the emission of nitrogen oxides (NOx). To balance emissions of the two pollutants, a divided flame was adopted. An air damper was installed to control the distribution of air to each combustion chamber, and three types of flame dividers were studied. The effects of the air-fuel ratio and combustion load on the NOx formation were investigated. The divided flame was found to reduce the NOx emission up to 25%, while keeping the CO to less than 10 ppm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.29-36
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• 2014

Hybrid rocket displays many different low frequency pressure oscillations during combustion. Thermal lag between solid and gas phase is the primary mechanism to trigger low frequency pressure oscillations of around 10Hz, and Helmholtz or $L^*$ mode also produces other types of low frequency oscillations above 10 Hz which is associated with the change in combustion volume. Since the flow characteristics in hybrid rocket is very similar to those in solid rocket combustion, it is not surprising to observe similar pressure oscillation behaviors. Experimental test shows that combustion pressure suddenly turns into to a big amplitude oscillation around 10Hz then followed by returning to an original pressure level after a short period combustion. Further investigations show that this instability is independent of the change in O/F ratio at all. One of the possible candidates is the vortex shedding dynamics over the backward step in the post combustion chamber. It is required to investigate the low frequency oscillation mechanism in the future study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.623-629
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• 2017

Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle's geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.585-592
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• 2016

Visualization was done by using $CH^*$ chemiluminescence images and PMT measurements in order to understand the origin of fluctuating pressure and chemical luminosity at about 500 Hz frequency even in stable combustion, which was observed in recent experimental tests, and to find the physical correlation leading to Low Frequency Instability(LFI) in terms of phase angle. In stable combustion, chemical reactions are distributed along the shear layer flow showing a negative coupling(about 180 degree in phase angle) with combustion pressure. However, phase difference is shifted to a positive coupling showing less than 90 degree in unstable case. Also a periodic change in the distribution of chemical reactions is observed along with local flame extinction and the appearance of big scale vortex flow. In the transition to LFI, local flame extinction and small vortex flow start to appear in a row. As seen in the bluff body wake in reactive flow, the periodic appearance of vortex flow seems to share the same physical process of BVK(Bernard Von Karman) instability generation. Thus, the appearance of local extinction in 500 Hz fluctuations is gradually amplified to complete extinctions of about 20 Hz, and it leads into LFI.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.454-460
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• 2009

To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ${\rho}_a=5.0kg/m^3$ to ${\rho}_a=12.3kg/m^3$ with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.567-574
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• 2018

Swirl injection induces not only the increase in fuel regression rate but also the reduction of combustion pressure oscillation. This acts, in turn, to stabilize combustion process. Thus, this study primarily focuses on the change in flow structure in the main chamber by swirl injection. Then examining the change in flow structure was done to understand the physical process for stabilizing combustion. In the results, the application of swirl injection could suppress the generation of p' and q' in 500Hz band and could shift the phase difference and cross correlation. Further investigations with combustion visualization also show that the development of helical motion near surface region affects the small-sized vortex generation and shedding yielding combustion stabilization eventually.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.4
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• pp.3991-4000
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• 1975

It is the aim of this study to investigate the influence of the factors in the sprayer nozzle for the travelling distance and to get nozzle design data in relation to the nozz1e with and without swirl plate. The factors of sprayer nozzle are composed of the spraying pressure, the helical angle of swirl plate, the helical groove depth of swirl plate, the distance of vortex chamber the slope of nozz1e cap, the curvature of nozzle cap and the hole diameter of nozz1e cap. The travelling distance and the size of sprayed particle are experimeted indoors by the factorial arrange-ment according to the 5 each level of the above factors. The results of this stupy are summarized as follows; 1. In the nozzle with swirl p1ate there were remarkable significance among factors each other, while without swirl plate were no significance. 2. The helical angle and groove depth in the nozzle with swirl plate were the highest effective factors. The effect of helical angle was very remarked in the quadratic curve with minium value. 3. The correlation betweenthe travelling distance and the sprayed particle size was no high and under 250 micron in the case with swirl plate, and there was higher correlation in the case without swirl plate. 4. The new ideal development of the swirl plate using of the most effective helical angle and groove depth will probably show the possiblities to make effective travelling distance over 8 meters and more over and to make average particle diameter under 300 micron.