• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.8-15
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• 2008

When a circular cylinder is placed at the center of a slot burner nozzle, once stable Woflhard-Parker type laminar lean premixed flame is changed to an oscillating flame with self-induced noise. The wrinkled flame surface showed the same pattern and frequency of the Karman vortex street at the downstream of a circular cylinder. The interaction of flame with Karman vortex street is observed to be responsible for flame oscillation. The measured flame oscillation frequency is very similar to the estimated Karman vortex shedding frequency based on the St-Re relationship of the flow past circular cylinder, which could be considered as a strong evidence for the interaction between laminar pre-mixed flame and a Karman vortex street. As Reynolds number increases oscillation frequency decreases and the self-induced noise level increases as well as the flame front is more severly wrinkled. This result suggests that the flame/vortex interaction becomes more active at higher Re.

• 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.25 no.8
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• pp.1087-1096
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• 2001

The dynamic structures of unsteady CH$_4$/Air jet diffusion flame with a flame-vortex interaction were numerically investigated. A timed-dependent, axisymmetric computational model and a low mach number approximation were employed in the present calculation. A two-step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including the gravitational effect show that the large outer vortices and the small inner vortices can be well simulated without any additional disturbances near nozzle tip. It was found that the temperature and species concentrations have deviated values even for the same mixture fraction in the flame-vortex interaction region. It was also shown that the flame surface is not deformed by the inner vortex in upstream region, while in downstream region, the flame surface is compressed or stretched by the outer vortex roll-up. The present unsteady jet flame configuration accompanying a flame-vortex interaction is expected to give good implications for the unsteady structures of turbulent flames.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.179-184
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• 2002

Interaction between flames and non-thermal plasmas of DBD type has been experimentally investigated. Vigorous streamers were observed under flame conditions because of the increase of reduced field (electrical) at high temperature as well as the seeding of free electrons and ions generated inside the flame. Flame lengths were significantly shortened as the applied voltage increased on account of intense mixing by ionic winds and soot-induced flows. Flame luminosities severely decreased under plasma conditions, which means the reduction of soot, since the residence time was reduced because of the flame shortening. Temperature and major species concentrations measured by FTIR were not changed despite the plasma generation. which shows overall chemistries were not affected by non-thermal plasmas.

• 한국연소학회:학술대회논문집
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• 1999.10a
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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.

• Journal of the Korean Society of Combustion
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• v.14 no.2
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• pp.32-41
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• 2009

The transported probability density function model combined with the consistent finite volume (FV) method has been applied to simulate the turbulent bluff-body reacting flows. To realistically account for the non-isotropic turbulence effects on the turbulent bluff-body reacting flows, the present PDF transport approach is based on the joint velocity- turbulent frequency-composition PDF formulation. The evolution of the fluctuating velocity of a particle is modeled by a simplified Langevin equation and the particle turbulence frequency is represented by the modified Jayesh - Pope model. Effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate this hybrid FV/PDF transport model, the numerical results are compared with experimental data for the turbulent bluff-body reacting flows.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1234-1243
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• 1990

Double coaxial are jets(annular and coaxial air jets) between which propane gas is fed was selected to study the structure of diffusion flames in turbulent shear flow. Schlieren and direct photographs are taken to visualize the flame structure. Mean and fluctuating temperatures and ion currents were measured to investigate the macroscopic and the instantaneous flame structure. The objective of this study is to understand the interaction between combustion and mixing process especially in the transition region of turbulent shear flow. The investigation reported in this paper focuses on the macroscopic and the instantaneous structures of three flames obtained. The increased mixing effect resulting from increase of Reynolds number of central air jet makes the flame bluish and short. When the velocity of surrounding air stream is higher than that of central air jet, the instantaneous flame structure is composed of coherent structure. It is considered that the flame structure of transitional region of mixing layer depends on the structure of mixing layer of non-reacting conditions.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.1
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• pp.47-58
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• 2023

Experimental data conducted by Colson et al. and numerical data conducted in this study were compared through counterflow flames to understand of the characteristic of basic flame about mixture of ammonia/methane. In order to use the suitable numerical mechanism, the validation was performed using total four mechanisms and the Okafor's mechanism showed satisfactory experimental results. The extinction boundary of the stability map could be explained through the effective Lewis number and the trend of LeD. The extinction behavior of the flame was different under the lean and rich symmetric conditions and it was investigated by the major variables, global strain rate (a_g) and mole fraction of ammonia (Ω_NH3).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.1
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• pp.7-14
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• 2008

It has been reported that partially premixed interacting flame could be sustained till sonic exit velocities if eight small nozzles are arranged optimally and one nozzle on the center is fed small amount of fuel. But the equivalence ratios in this experiments were 20-60. In this research, experiments were conducted to know the effects of lean-rich staging in multiple jet flames on the blowout velocity. The fuel mole tractions in the fuel-air mixture, the nozzle exit velocity and the diameter between adjacent nozzles were alternatively changed. When the lower mole fraction fuel was fed to the nozzles located near the center and small amount of fuel to the center nozzle, flame was not extinguished even at the nozzle exit velocity of 200m/s. Also the interacting flame could be sustained till that velocity when four small size nozzles for lean mixture were located within the arrangement of four nozzles for rich mixture and configured optimally.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.991-1000
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• 1987

Existence of triple flames in a lean-rich concentration field is studied both experimentally and theoretically using large activation energy asymptotic technique adopting counterflow system as a model problem. Experiment shows that in triplet system of a lean and a rich premixed flame separated by a diffusion flame, either lean or rich premixed flame merges with diffusion flame as stretch is increased, such that transition boundary between 3-flame and 2-flame exists. The region in which 3-flame can exist forms an island within rich-lean concentration fields for large stretch, where as it is extends to the line of (.OMEGA.$_{0}$/.OMEGA.$_{F}$)$_{R}$=0 or (.OMEGA.$_{F/}$.OMEGA.$_{0}$)$_{L}$=0 for small stretch. Theoretical results show the qualitative agreement with experiment and the existence of limiting stretch over which 3-flame can not exist.t.t.t.t.t.t.