• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.217-228
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• 2000

Circulating Fluidized Bed Combustor(CFBC) has been used for the incineration of waste sewage sludge and for the power generation. In this study hydrodynamic characteristics of two phase flow have been studied in a riser section of CFBC. A lab-scale riser is designed and SiC (Geldart type B) is used for solid particles. Experiments are performed by controlling the fluidization parameters including superficial velocity and secondary air to primary air ratio for determination of solid holdup profiles in the riser. Superficial velocities of each fluidization regime are well agreed with results predicted by a theoretical model. The results show that the axial solid holdup distributions calculated by measuring differential static pressures in the riser are found to show a basic profile described by a simple exponential function. Our flow regime during experiments mainly belongs to fast fluidization regime for particle size of 300${\mu}m$. As the SA/PA ratio increases, solid holdup in the lower dense region of the riser increases.

• 한국추진공학회지
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• 제1권2호
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• pp.22-31
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• 1997

비직교 일반좌표계를 사용하는 범용 연소유동해석 프로그램을 개발하여 재순환영역을 가지는 연소유동 등을 해석하였다. 본 프로그램은 유한체적법에 근간을 둔 비엇갈림격자계를 사용하며 직교좌표 속도성분을 종속변수로 하였다. 연소모델은 무한반응속도의 1단계 비가역 반응을 고려하였으며, 밀도가중평균된 지배방정식을 고려하였다. Conserved Scalar의 확률밀도함수를 clipped gauss 분포로 가정하였다 본 프로그램을 사용하여 재순환영역을 가지는 난류확산화염을 계산하였다. 계산결과는 실험결과와 마찬가지로 두개의 재순환영역을 보였으며, 속도, 난류운동에너지, 온도 및 농도 등이 실험결과와 양호하게 일치하는 결과를 얻을 수 있었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제20회 KOSCO SYMPOSIUM 논문집
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• pp.189-196
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• 2000

A numerical simulation was conducted to analyze the interaction of flame and vortices. The characteristic scales of flame and vortices were limited in the thin laminar flamelet regime. Within this regime, flame is assumed as discontinuity surface and its motion in flow field was described by G-equation instead of full governing equations. Additional approximations include distribution of line volume sources on flame surface to simulate effect of volume expansion. Contrast to previous calculations, current study employed vortex transport equation to evaluate attenuation and smearing of vortices. Two extreme conditions of frozen vortex and frozen flame were considered to validate the current method. Comparison with direct numerical simulation resulted in satisfactory quantitative agreement with higher computational efficiency which warrants the usefulness of the present model in more complex situation.

• 대한기계학회논문집B
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• 제36권11호
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• pp.1065-1072
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• 2012

바이오디젤 연료는 그 안에 포함된 산소성분으로 인해 압축착화엔진에 사용했을 때 일반디젤 연료보다 더 적은 입자상 물질을 배출한다. 따라서 이 연료를 저온연소 기법에 적용하는 경우 보다 효과적으로 $NO_x$-PM을 동시 저감할 수 있고 그로부터 저온연소 운전영역의 확장을 기대할 수 있다. 이번 연구에서는 일반디젤과 대두유 기반의 바이오디젤 연료를 이용하여 산소농도 5~7%의 Dilution controlled regime에서 저온연소 운전을 구현하고 성능 및 배기 특성을 조사하였다. 엔진 실험 결과로부터 바이오디젤 연료의 경우 디젤에 비해 약 14% 낮은 발열량에도 불구하고 높은 세탄가 및 함산소 성질로 인한 연소효율 증가로 동일 연료량 분사 시 이보다 더 낮은 약 10~12% 정도의 출력이 감소함을 볼 수 있었다. 배기 측면에서도 바이오디젤 내 산소원자가 입자상물질의 산화반응을 촉진하여 최대 90%의 smoke 저감이 가능함을 관찰하였다. 또한 엔진 과급 실험으로부터 과급을 사용하여 저온연소 및 바이오디젤 사용으로 인한 출력 저하를 개선할 수 있음을 확인하였으며 과급과 바이오디젤 연료의 동시 적용을 통해 산소농도 11~12%의 EGR 가스 투입으로도 저온연소에 상응하는 PM-$NO_x$ 동시 저감이 가능함을 보여주었다. 이런 결과는 결국 이와 같은 과급 및 바이오디젤 연료의 적절한 조합으로부터 엔진 출력 향상과 배기특성 개선이 동시에 달성할 수 있고 이로부터 운전영역의 확대가 가능함을 의미한다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.11-20
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• 1999

Acoustic pressure response and NO formation of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such non-monotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. Acoustic pressure response in each regime is investigated based on the Rayleigh criterion. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted. Emission index of NO shows similar behaviors as to the peak-temperature variation with pressure.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.47-54
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• 1999

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength assigned by the density difference between the burned and the unburned region. The present model provides good agreement with the experimental results by using realistic volume expansion ratio which was not reached in the previous researches. Including volume expansion, the flow predicts the same behavior of measured velocity field qualitatively. The flame propagation in varying flow field due to volume expansion provides a promising way to represent the wrinkled turbulent premixed flames in a numerically efficient manner.

• 한국자동차공학회논문집
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• 제3권6호
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• pp.78-86
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• 1995

The structure of premixed turbulent flames in a constant-volume vessel was investigated using a microprobe method. The flame potential signal having one to eight peaks was detected in the case of turbulent flames, each of them being regarded as a flamelet existing in the flame zone. Based on this consideration, the flame propagation speed, the thickness of the flame zone, the number of flamelets and the separation distance between adjacent flamelets in the flame zone were measured. The experimental resuits of this work suggest the existence of "reactant islands" behind the flame front when the turbulence was intensified to some extent. The critical(lowest) ratio of turbulence intensity to the laminar burning velocity being found to be about 0.7 for the formation of reactant islands in this experiment.

• 한국연소학회지
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• 제9권2호
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• pp.1-9
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• 2004

Activation energy asymptotics (AEA) for Linan#s diffusion-flame regime is revisited in this paper. The main purpose of the paper is to carefully re-examine each AEA analysis step in order to clarify the some concepts that are often misunderstood among the ordinary practitioners of the AEA. Particular attention is focused on the different AEA regimes arising from the double limit of large Zel#dovich and Damkohler numbers. In addition, the expansion procedures are shown in detail and the method that the turning point condition, commonly known as the Linan#s extinction condition, is found is explained.

• 한국연소학회지
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• 제9권1호
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• pp.32-38
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• 2004

Characteristics of turbulent lifted flames in coflow jet have been investigated by varying initial temperature through the heating coflow air. In the turbulent regime, liftoff height increases linearly with fuel jet velocity and decreases nonlinearly as the coflow temperature increases. This can be attributed to the increase of turbulent propagation speed, which is strongly related to laminar burning velocity. Dimensionless liftoff heights are correlated well with dimensionless jet velocity, which are scaled with parameters determining local flow velocity and turbulent propagation speed. This implies that the turbulent lifted flames are stabilized by balance mechanism between local turbulent burning velocity and flow velocity. Blowout velocity can be obtained from the ratio of mixing time to chemical time. Comparing to previous researches, thermal diffusivity should be evaluated from the initial temperature instead of adiabatic flame temperature.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.260-265
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• 2008

A numerical scheme for solid propellant rocket has been studied using preconditioning method to research unsteady combustion processes for the double-base propellant with a converging-diverging nozzle. The Navier-Stokes equation is solved by dualtime stepping method with finite volume method. The turbulence model uses a shear stress transport modeling. The species equation follows up the method of Xinping WI, Mridul Kumar and Kenneth K. Kuo. A preconditioned algorithm is applied to solve incompressible regime inside the combustor and compressible flow at nozzle. Mass flux was evaluated using modified advective upwind splitting method. The simulated result the comparison a fully coupled implicit method and a semi implicit method in terms of accuracy and efficiency. This report shows the result of solid rocket propellant combustion.