• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.81-91
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• 1999

Fuel characteristics of sewage sludge as required for the fluidized bed incinerators have been evaluated. Sewage sludge is basically a solid fuel with high percentage of moisture. Moisture content of the fuel directly affects the heating value of the fuel and the exhaust gas composition. When the sludge of transported into the incinerator, sludge cake is subject to the mixing, break-up and heat-up. Fluidization process would enhance these physical processes. The sludge fuel could then undergo the moisture evaporation and devolatilization process. Subsequent oxidation of volatiles as well as the remaining char would then follow. Sludge samples are characterized with high percentage of volatiles out of total combustibles. Quantitative understanding of above listed subprocesses would certainly help in the utilization of fluidized bed incinerators. A limited set of fuel characterization tests including calorimetric analysis, proximate analysis, elemental analysis and thermogravimetric analysis were conducted for the selected sludge samples. The measurement reasults of sludge samples were reported along with some published data. Limited experience in the actual incinerator plant is also presented.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.95-103
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• 2019

Vapor explosions can be classified in terms of modes of contact between the hot molten fuel and the coolant, since different contact modes may affect fuel-coolant mixing and subsequent vapor explosion energetics. It is generally accepted that most vapor explosion phenomena fall into three different modes of contact; fuel pouring into coolant, coolant injection into fuel and stratified fuel-coolant layers. In this study, we review previous stratified steam explosion experiments as well as recent experiments performed at the KTH in Sweden. While experiments with prototypic reactor materials are minimal, we do note that generally the energetics is limited for the stratified mode of contact. When the fuel mass involved in a steam explosion in a stratified geometry is compared to a pool geometry based on geometrical aspects, one can conclude that there is a very limited set of conditions (when melt jet diameter is small) under which a steam explosion is more energetic in a stratified geometry. However, under these limited conditions the absolute energetic explosion output would still be small because the total fuel mass involved would be limited.

• 한국연소학회지
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• 제4권1호
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• pp.117-129
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• 1999

A method for the mixing augmentation of the transverse injection of fuel in a Scramjet combustor is suggested. Based on the fact that the main factor controlling the mixing characteristics in transverse injection is the effective back-pressure (the pressure around the injection hole) it is tried to make a flow expansion near the injection port in order to reduce effective back-pressure. A three dimensional Navier-Stokes code adopting the upwind method of Roe#s flux difference splitting scheme is used. The k-w SST turbulence model turbulence model is used to calculate the turbulent viscosity. It is shown that the reducing of the effective back-pressure make it possible to increase the penetration distance and to increase the mixing rate without excessive losses of stagnation pressure. Also, it is shown that the streamwise vorticity generated by baroclinic torque has great influences on the mixing process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1900-1905
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• 2007

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio (${\Phi}$), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$ < 1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

• 동력기계공학회지
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• 제19권1호
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• pp.56-63
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• 2015

In this study, the exhaust characteristics of the diesel engine for the change of the mixing ratio of biodiesel fuel were quantitatively analyzed by using the numerical analysis method. As the fuel used in the experiment, the diesel and biodiesel(waste oil, soybean oil), the mixed fuel BD2(Diesel only), BD3, BD5, BD20, BD50 and BD100 were used. The injection pressure($p_{inj}$) was set to 400bar, 600bar, 800bar, 1000bar and 1200bar as the experimental variable. Also the concept of the standard deviation, Pearson's correlation coefficient and Spearman rank-order correlation coefficient based on the statistics was introduced in order to analyze the exhaust characteristics of the quantitative NOx and Soot according to the injection pressure and the mixing ratio variation of biodiesel blending fuel. It is considered that as a result of studies, for the waste oil, NOx and Soot can be simultaneously reduced through control of the mixing ratio at the regions of $p_{inj}=400bar$ and $p_{inj}=600bar$, and the Soot can be reduced without affecting on the emission of NOx at more than $p_{inj}=800bar$. For the soybean oil, NOx and Soot can be simultaneously reduced at $p_{inj}=400bar$ and the Soot can be reduced without affecting on the emission of NOx at $p_{inj}=600bar$.

• 대한기계학회논문집B
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• 제31권12호
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• pp.1042-1047
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• 2007

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio ($\Phi$), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$<1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

• 한국분무공학회지
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• 제13권1호
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• pp.1-8
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• 2008

It was investigated how fuel injection timing - early injection and later injection - in conjunction with throttle open rate effect the fuel-air mixing characteristics, Engine power, combustion stability and emission characteristics on a DI CNG spark Engine and control system that had been modified and designed according to the author's original idea. It was verified that the combustion characteristics were changed according to fuel injection timings and Engine conditions determined by different throttle open rates and rpm. It was found that the combustion characteristics greatly improved at the complete open throttle rate with an early injection timing and at the part throttle rate with a late injection timing. Combustion duration was governed by flame propagation duration in a late injection timing and by an early flame development duration in an early injection timing. As the result, we discovered that combustion duration is shortened, lean limit is improved, air-fuel mixing conditions controlled, and emissions reduced through control of fuel injection timing according to change of the throttle open rate.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제23회 추계학술대회 논문집
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• pp.274-277
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• 2004

ATR 엔진 연소기 내부에서의 연료와 공기의 혼합성능은 연소 안정성이나 효율에 지배적인 요인이 된다. 본 연구에서는 ATR 모델 연소기에서의 혼합성능을 비교하기 위하여 두 유체의 속도 비$(r=v_a/v_f)$를 변화시키면서 연료분포를 측정하였다. 측정 방법으로는 2차원 연료분포를 얻기 위하여 널리 이용되는 평면레이저 유도형광기법과 화상처리 기법을 사용하여 연료분포 이미지를 얻었다. 측정된 연료분포 화상으로부터 공기속도/연료속도 비가 1에 가까울수록 연료 혼합성능이 떨어지는 특성을 관찰하였다.

• 한국연소학회지
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• 제3권1호
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• pp.41-48
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• 1998

A numerical study on combustion in a fluidized bed is based on three dimensional mixing and dispersion phenomena in the bed owing to the bubble growth in the vertical direction. As fluidizing velocities increase, bubble diameters increase, which activates the fuel dispersion in the bed. The combustion rates, however, reduce due to the decrease of gas exchange rates between bubble and emulsion phases. Fuel distributions in the bed are dependent on fluidizing velocities, equivalence ratios, fuel particle diameters, fuel feeding points, and the number of fuel feeders.

• 연구논문집
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• 통권31호
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• pp.23-43
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• 2001

An experimental investigation on the reduction of nitrogen oxide emission from swirling, turbulent diffusion flames was conducted using multi air staged combustor, The combustor utilizes swirler to dampen fuel/air mixing, allowing an extended residence time for fuel pyrolysis and fuel-N conversion chemistry in an locally fuel-rich environment prior to burnout. This process also allow to reduce thermal NOx formation to lessen the temperature of reaction zone. The aerodynamic process therefore emulates the conventional staged combustion process, but without the need for the physically separate fuel-rich and -lean stages. Parametric studies on the ratios of each staged air and droplet size were carried out the feasibility of fuel/air mixing for low NOx combustion with diesel and pyridine mixed diesel fuel oil.