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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Society of Combustion
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Journal DOI :
The Korean Society of Combustion
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Volume & Issues
Volume 5, Issue 2 - Dec 2000
Volume 5, Issue 1 - Jun 2000
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Flamelet Modeling of Thrbulent Nonpremixed Flames
Kim, Yong-Mo ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 1~8
The flamelet concept has been widely applied to numerically simulate complex phenomena occurred in nonpremixed turbulent flames last two decades, and recently broadened successfully the applicable capabilities to various combustion problems from simple laboratory flames to gas turbine engine, diesel spray combustion and partially premixed flames. The paper is focused on brief review of recently noticeable work related to flamelet modeling, which includes Lagrangian flamelet approach, RIF concept as well as steady flamelet approach. The limitation of steady flamelet assumption, the effect of transient behavior of flamelets, and the effect of spray vaporization on PDF model have been discussed.
Conditional Moment Closure Modeling in Turbulent Nonpremixed Combustion
Huh, Kang-Y. ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 9~17
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.
Edge Flame : Why Is It So Hot in Combustion?
Kim, Jong-Soo ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 19~27
A turbulent combustion model, based on edge flame dynamics, is discussed in order to predict global extinction of turbulent flames. The model is applicable to the broken flamelet regime of turbulent combustion, in which global extinction of turbulent flame is achieved by gradual expansion of flame holes. The edge flame dynamics is the key mechanism to describe the flame hole expansion or contraction. For flames with Lewis numbers near unity, there is a
number, namely the crossover
number, at which edge flame changes its direction of propagation. The parametric region between the quasi-steady extinction condition and the edge-flame crossover condition is a metastable region, in that flames without edge can stay in their burning states while flames with edge have to retract to expand quenching holes. Using the above properties of edge flame, Hartley and Dold proposed a Lagrangian hole dynamics, which allows us to simulate transient variation of quenching holes. In their model, each stoichiometric surface is subjected to a random sequence of scalar dissipation rate compatible to the equilibrium turbulence. Then, each stoichiometric surface will evolve, according to the combustion map, dependent on the scalar dissipation rate and existence of flame edge, If all the burning surfaces are annihilated, the event can be declared as a global extinction. The consequence obtained from the above model also can be used as a subgrid model to determine local extinction occurring in a calculation grid.
Investigation of the Knocking Phenomenon in SI Engines
Min, Kyoung-Doug ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 29~35
Knock in SI engines causes physical damage to the piston and combustion chamber and lowers the thermal efficiency. The increase in compression ratio which can improve the thermal efficiency and engine performance has been limited by engine knock. So the need of making clear the knocking phenomenon has increased. This paper reviews the methods of knock detection, characterization and prediction of knock with the reduced chemical kinetic modeling.
Numerical Study of the Effects of Hydrocarbon Addition and Corresponding Chemical Kinetics on the Promotion of NO Oxidation in Nonthermal Plasma DeNOx Treatment
Shin, Hyun-Ho ; Yoon, Woong-Sup ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 37~50
In the present study, a systematic chemical kinetic calculations were made to investigate the augmentation of
conversion due to the addition of various hydrocarbons (methane, ethylene, ethane, propylene, propane) in the nonthermal plasma treatment. It is included in the present conclusion that the reaction between hydrocarbon and oxygen radicals induced by electron collision, is believed to be a primarily process for triggering the overall NO oxidation and the eventual NOx reduction. Upon the completion of the initiating step, various radicals (OH,
etc.) successively are produced by hydrocarbon decomposition form the primary path of
conversion. When the initiating step is not activated, hydrocarbon consumption rate appeared to be very low, thereby the targeted level of NO conversion can only be achieved by the addition of more input energy. Present study showed ethylene and propylene to have higher affinity with O radical under all conditions, thereby both of these hydrocarbons show very fast and efficient
oxidation. It was also shown that propylene is superior to ethylene in the aspect of NOx removal.
The Effect of Flame Radiation on NOx Emission Characteristics in Hydrogen Thrbulent Diffusion Flames
Kim, Seung-Han ; Kim, Mun-Ki ; Yoon, Young-Bin ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 51~62
The relationship among the flame radiation, NOx emissions, residence time, and global strain rate are examined for turbulent non-premixed jet flames with wide variations in coaxial air conditions. Measurements of NOx emission, flame geometry and flame radiation were made to explain the NOx emission scaling based on global parameters such as flame residence time, global strain rate, and radiant fraction. The overall 1/2-power scaling is observed in coaxial air flames, irrespective of coaxial air conditions, but the degree of deviation from the 1/2-slope curve in each case differs from one another. From the comparison between the results of pure hydrogen flames and those of helium diluted hydrogen flames, it is observed that flame radiation plays a significant role in pure hydrogen flames with coaxial air and the deviation from 1/2-power scaling may be explained in two reasons: the difference in the flame radiation and the difference in jet similarity in coaxial air flames. From the radiation measurements, more detailed explanations on these deviations were suggested.
Combustion Characteristics in Small Combustion Chamber Size about Quenching Distance
Lee, Dae-Hoon ; Choi, Kwon-Hyoung ; Kwon, Se-Jin ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 63~68
Combustion phenomenon in scale-downed combustor is investigated. As the combustor scale decreases surface to volume ratio increases and chamber size approaches quenching distance. As the combustor scales down surface to volume ratio increases resulting increased heat loss. And this heat loss can affect quenching and instability of the flame. To investigate this effect plastic mini combustor is made. Stoichiometricaly premixed Hydrogen / air gas is used as fuel. Initial chamber pressure and chamber size are varied and the effects are evaluated. Peak pressure decreased with the decrease in chamber height. As initial chamber pressure decreases peak pressure decreases and this change is more important than scale down effect till the chamber height of 1mm. With this result and further information following the experiments design parameter for micro engine can be established.
Study on Reattachment in Axisymmetric Laminar Lifted Flames
Lee, Jong-Soo ; Chung, Suk-Ho ;
Journal of the Korean Society of Combustion, volume 5, issue 2, 2000, Pages 69~78
Reattachment characteristics of laminar flames in partially premixed jets are studied for propane fuel mixed with air. As the flow rate decreases, liftoff height is decreased nonlinearly and the flame reattaches to a nozzle at a certain liftoff height. Using a jet theory by taking into account a virtual origin, it is predicted that flow velocity along a stoichiometric contour has a maximum value near nozzle. With this velocity characteristics, it is shown that reattachment mechanism can be explained by a balance between flame speed and flow velocity. Predicted displacement speeds at reattachment and liftoff agree qualitatively well with experimental findings.