• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.63-64
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• 2012

The present study has numerically investigated the effects of the fuel-side nitrogen dilution on the precise structure and NOx formation characteristics of the turbulent syngas nonpremixed flames. Numerical results indicate that for highly diluted case, the flame structure is dominantly influenced by the turbulence-chemistry interaction and marginally modified by the radiation effect. On the other hand, no-dilution case with the longer flight time and the relatively intermediate scalar dissipation rate is influenced strongly by the radiative cooling as well as moderately by the turbulence-chemistry interaction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.114-122
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• 1999

Reignition as special cases of acoustic pressure responses of flame are numerically studied by employing methanol droplet flame as a laminar flamelet. Quasi-steady flame responses occur in the range of small amplitude, low frequency oscillation. Reignition phenomena can occur when, by increasing the frequency of large amplitude acoustic pressure, the magnitude of characteristic acoustic time is the same order of that of characteristic reaction time of flames. And more increasing of amplitude of acoustic pressure induces the direct extinction of flame. Flame can sustain its own intensity even under the steady extinction temperature in case of high frequency acoustic oscillation, and this tendency is remarkable with increasing frequency. Reignition regime with respect to amplitude and frequency of acoustic pressure doesn't exist in low frequency($10^2$ Hz, in this study), but broadens with frequency of acoustic pressure.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.437-441
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• 2010

LES results of turbulent premixed combustion flows are introduced by using the dynamic sub-grid scale model based on G-equation describing the flame front propagation. The turbulent premixed combustion flows around bluff body and over backward facing step are analyzed to validate present formation. LES of swirling partially premixed combustion flame is also performed to conform the predictive capabilities of LES model and to prompt our understanding for the combustion flows over double cone swirl burner combustor by using CFD-ACE+ commercial code.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.29-35
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• 2001

Radiation-induced oscillatory instability in CH$_4$/Air diffusion flames is numerically investigated by adopting detailed chemistry. Counterflow diffusion flame is employed as a model flamelet and optically thin gas-phase radiation is assumed. Attention is focused on the extinction regime induced by radiative heat loss, which occurs at low strain rate. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Depending on the initial strain rate and the amount of perturbed strain rate, transient evolution of the flame exhibits various types of flame-evolution behaviors. Basically, the dynamic behaviors can be classified into two types, namely oscillatory decaying solution and diverging solution leading to extinction.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.33-39
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• 2002

Unsteady behaviors of counterflow flame were studied experimentally in opposing jet counterflow burner using diluted methane. To generate the unsteadiness on the flame, the counterflow diffusion flame was perturbed by velocity changes made by the pistons installed on both sides of the air and fuel stream. The velocity changes were measured by Hot wire and Laser Doppler Velocimetry, and the flame behaviors were observed by High speed ICCD and ICCD. In this investigation, the spatial irregularity of the strain rate caused the flame to extinguish from the outside to the axis during the extinction, and we found the following unsteady phenomena. First, the extinction strain rates of unsteady cases are much larger than those of the steady ones. Second, the extinction strain rates become larger as the slope of the change of the strain rate increases. Third, the unsteady extinction strain rates become smaller with the increase of the initial strain rate.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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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.

• Journal of ILASS-Korea
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• v.14 no.4
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• pp.163-170
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• 2009

The present study has numerically investigates the vaporization, auto-ignition and combustion processes in the high-pressure and high-temperature conditions encountered in the diesel engine. In the present study, in order to understand the overall spray combustion characteristics of DME fuel as well as to identify the distinctive differences of DME combustion processes compared to conventional hydrocarbon liquid fuels, the sequence of the comparative analysis has been systematically made for DME and n-Heptane liquid fuels. Computations for DME fuel are made for two cases including constant fuel mass flow rate condition and fixed heat release rate. Based on numerical results, the discussions are made for the detailed combustion processes of DME and n-Heptane spray.

• Journal of the Korean Society of Combustion
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• v.5 no.2
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• pp.9-17
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• 2000

A brief introduction is given on the conditional moment closure model for turbulent nonpremixed combustion. It is based on the transport equations derived through a rigorous mathematical procedure for the conditionally averaged quantities and appropriate modeling forms for conditional scalar dissipation rate, conditional mean velocity and reaction rate. Examples are given for prediction of NO and OR in bluffbody flames, soot distribution in jet flames and autoignition of a methane/ethane jet to predict the ignition delay with respect to initial temperature, pressure and fuel composition. Conditional averaging may also be a powerful modeling concept in other approaches involved in turbulent combustion problems in various different regimes.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1240-1247
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• 2006

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by using G-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgrid G-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic sub grid G-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.

• 한국연소학회:학술대회논문집
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• 2013.06a
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• pp.123-126
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• 2013

Combustor development requires high fidelity simulation capable of predicting recirculation zone (RZ), temperature field, and pollutant emission. Swirling flow is widely used in combustor for its benefits in efficient mixing and flame stabilization by RZ. Large eddy simulation (LES) is used to calculate swirling flow in an expanding pipe [1], and shows higher accuracy than RANS. Reactive flow modeling using LES and flamelet model is validated with experiments by Barlow et al. [4] and Masri et al. [3]. Finally, heat transfer simulation of Samsung Techwin's combustor liner is presented.