• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.49-56
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• 2003

Mathematical formulation of the zone conditional two-fluid model is established to consider flame-generated turbulence in premixed turbulent combustion. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin flamelets. The transverse component of rms velocities in burned zone become larger than axial component in the core of turbulent flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.62-69
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• 2004

Zone conditional formulations for the Reynolds average reaction progress variable are used to derive an asymptotic expression for turbulent burning velocity. New DNS runs are performed for validation in a statistically one dimensional steady state configuration. Parametric study is performed with respect to turbulent intensity, integral length scale, density ratio and laminar flame speed. Results show good agreement between DNS results and the asymptotic expression in terms of measured maximum flame surface density and estimated turbulent diffusivity in unburned gas.

• Journal of the Korean Society of Combustion
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• v.9 no.4
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• pp.1-8
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• 2004

Zone conditional formulation for the Reynolds average reaction progress variable is used to derive an asymptotic expression for turbulent burning velocity. New DNS runs are performed for validation in a statistically one dimensional steady state configuration. Parametric study is performed with respect to turbulent intensity, integral length scale, density ratio and laminar flame speed. Results show good agreement between DNS results and the asymptotic expression in terms of measured maximum flame surface density and estimated turbulent diffusivity in unburned gas.

• Journal of the Korean Society of Combustion
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• v.8 no.4
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• pp.15-23
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• 2003

The zone conditional two-fluid equations are derived and validated against DNS database of a premixed turbulent flame. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin f1amelets. The transverse component may be larger than the axial component for a distributed pdf of the flamelet orientation angle, while the opposite occurs due to redistribution of turbulent kinetic energy and flamelet orientation normal to the flow at the end of a flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface. Ad hoc modeling of some interfacial terms may be required for further application of the two-fluid model in turbulent combustion simulations.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.14-20
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• 2005

내연기관 연소는 난류유동, 분무, 연소, 열전달의 복합적인 현상으로서 열역학적 해석이 주류를 이루어 왔으나 컴퓨터의 발전에 따라 효율 개선과 공해 저감을 목표로 전산유체해석 기법이 적극적으로 도입되고 있다. 내연 기관 연소의 근간을 형성하는 난류 연소 모델링의 기본 개념으로서 가솔린엔진에서의 예혼합연소와 디젤엔진에서의 확산연소에 대한 영역조건평균(zone conditional averaging) 모델과 조건평균닫힘(conditional moment closure) 모델에 대해 설명하였으며 $NO_x$와 soot 예측에 대한 적용과 엔진응용 사례를 소개하였다.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.41-45
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• 2002

The zone-conditioned CMC equations are derived by taking an unconditional average of the generic conservation equations multiplied by delta and Heaviside functions in terms of mixture fraction and reaction progress variable. The resulting equations are essentially in the same form as the single zone CMC equations except for separate flow fields for burned and unburned gas. The zone-conditioned two-fluid equations are applied to a stagnating turbulent premixed flame brush of Cheng and Shepherd[5l. It is shown that the flame stretch factor is of crucial importance to accurately reproduce the measured mean reaction progress variable and conditional velocities. Further work is in progress for the relationship between surface and volume averages and extension to partially premixed combustion on the basis of a triple flame structure, e. g. in a lifted turbulent diffusion flame.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.23-30
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• 2008

An analytical expression for the turbulent burning velocity is derived from the asymptotic zone conditional transport equation at the leading edge. It is given as a sum of laminar and turbulent contributions, the latter of which is given as a product of turbulent diffusivity in unburned gas and inverse scale of wrinkling at the leading edge. It was previously shown that the inverse scale is equal to four times the maximum flame surface density in the wrinkled flamelet regime [1]. The linear behavior between $U_T$ and u' shows deviation with the inverse scale decreasing due to the effect of a finite flamelet thickness at higher turbulent intensities. DNS results show that $U_T/S^0_{Lu}$ may be given as a function of two dimensionless parameters, $u'/S^0_{Lu}$ and $l_t/\delta_F$, which may be transformed into another relationship in terms of $u'/S^0_{Lu}$, and Ka. A larger $l_t/{\delta}_F$ or a smaller Ka leads to a smaller scale of wrinkling, hence a larger turbulent burning velocity in the limited range of $u'/S^0_{Lu}$. Good agreement is achieved between the analytical expression and the turbulent burning velocities from DNS in both wrinkled and thickened-wrinkled flame regimes.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.31-43
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• 2008

Oxy-fuel flame has a significantly different structure from that of air-fuel flame because of its high temperature. This study is aimed to find out the difference of the oxy-fuel flame structure in order to understand reaction mechanism closely, which is crucial to design real-scale oxy-fuel combustion system. By examining pictures of counterflow flame and LIF images, we found that oxy-fuel flame had two-zone structure: fuel decomposition region and distributed CO oxidation region. In the oxy-fuel flame, OH radical was distributed intensely through the whole flame due to its higher flame temperature than crossover temperature. For showing those features of the oxy-fuel flame, 1 MW scale IFRF oxy-natural gas burner was simulated by conditional moment closure(CMC) model. Calculation results were compared with experimental data, and showed agreements in trend. In the simulated distributions of fuel decomposition/CO oxidation rates, CO oxidation region was also separated from fuel decomposition zone considerably, which showed the two-zone structure in the oxy-fuel flame.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.230-240
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• 1990

An exprimental research has been carried out to find the intermittent flow pattern in the transition region of a turbulent round jet in order to elucidate detailed turbulence structure and to accumulate basic data necessary for computational turbulence modelling. Turbulent signals were processed digitally to obtain conventional or conditional velocity components. The high-order conditional correlations obtained in this study showed similar trends as those of other free shear flows. It was found that the non-turbulent fluid contributes negligibly to the turbulent kinetic energy production and its diffusive transport and that the diffusion by bulk convection has the same order of magnitude as the gradient diffusion in the free boundary region. The statistical analyses such as flatness factor, skewness factor and probability density functions of turbulent and non-turbulent zone durations have also been performed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.3
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• pp.222-229
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• 2009

A noble infrared sensor was studied for passenger conditional detection in vehicle, This research relates to uncooled infrared sensors for detecting the presence, type and temperature of occupants in vehicle. It sense that the occupants purpose to control the smart airbag for safety in the case of adult or child and to control the automatic air conditioning for convenience. This paper described the design and the fabrication of microbolometers which were composed of 2 by 8 elements using the surface micromachining technology. The characteristics of the array were investigated in the spectral region of $8{\sim}12{\mu}m$. The fabricated detectors exhibited the thermal mass of $7.05{\times}10^{-9}\;J/K$, the thermal conductance of $1.03{\times}10^{-6}\;W/K$, the thermal time constant of 6.8 ms, the responsivity of $2.96{\times}10^4\;V/W$ and the detectivity of $1.01{\times}10^9\;cmHz^{1/2}/W$, at the chopper frequency of 10 Hz and the bias current of $4.4{\mu}A$. We could successfully detect the human body condition in the divided zone. As a results, we concluded that microbolometer optimized in this research could be useful for the application of passenger conditional detection in vehicle.