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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 2, Issue 1 - Dec 1997
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Numerical Study of Premixed Combustion within a Porous Ceramic Burner of Different Ceramic Properties
Lim, In-Gweon ;
Journal of the Korean Society of Combustion, volume 2, issue 1, 1997, Pages 1~8
Premixed combustion within porous ceramic media is numerically studied to understand burning characteristics and to find best configurations for burner implementations. Among many parameters, critical to burner performance, flame location and extinction coefficient are selected as major parameters for this study. The flame structure and burner performance with respect to these two parameters are observed. In the study, it is found that the location of flame is the most important in porous burner operation since it affects the rate of heat transfer and flame structure. Stability of the flame within the porous ceramic burner is discussed with respect to the flame location. It is found that to obtain high radiative output, the flame should be located downstream section of the burner. But the flame is to be unstable at most of downstream section except near the exit plane. To overcome this problem, new porous ceramic burner, using different ceramic properties in one burner instead of single property ceramic, is made and tested. With a combination of ceramics of high extinction coefficient at upstream and another material of low extinction coefficient at downstream of the burner, the flame can be stabilized at wider region of the burner with higher radiative output compared to the original burner configuration.
Stability Analysis of Reacting Wakes
Shin, D.S. ; Hong, S.J. ; Park, S.H. ;
Journal of the Korean Society of Combustion, volume 2, issue 1, 1997, Pages 9~16
This paper investigates the linear stability of wakes with special emphasis on the difference of velocity and density. Velocity and density profiles for laminar flows have gaussian profiles. Incompressible wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. Sinuous modes are more unstable than varicose modes irrespective of density variation, which shows wakes will be destabilized by sinuous modes. Large velocity difference and density difference leads to more unstable wakes due to large momentum difference.
A Study on NOx Reduction Mechanism in a Closed Vessel with Opposed Dual Pre-chambers
Kim, Jae-Heon ; Lee, Soo-Gab ; Jeung, In-Seuck ;
Journal of the Korean Society of Combustion, volume 2, issue 1, 1997, Pages 17~27
It is well known that NOx formation has a strong dependence on the maximum temperature and correspondingly with the maximum chamber pressure of a closed combustion system. However, in a case of impinging-jet-flame (IJF hereafter) combustion with opposed dual pre-chambers, low
formation with high pressure could be achieved, but its mechanism has not been clearly understood so far. In this study, a three-dimensional analysis is adopted to resolve time-variant local properties that might indicate the mechanism of IJF combustion. Numerical results are verified by comparing them with experiments. The IJF combustion in a vessel with no pre-chamber, with single pre-chamber, and with dual pre-chambers is studied. The orifice diameter and the volumetric ratio of pre-chamber are used as geometric parameters. The effects of main-chamber ignition delay time and combustion time of main-chamber, orifice exit velocity, orifice exit temperature, turbulent kinetic energy of main-chamber and spatial distribution of temperature in the latter stage of combustion are investigated. A longer main-chamber ignition delay and a shorter main-chamber combustion time suppress the formation of high temperature region with respect to mean temperature, which consequently results in less NO production.
Effects of Catalytic Reaction and Natural Convection on the Hot Surface Ignition of Methane-Air Mixtures
Kim, H.M. ; Jurng, J.S. ;
Journal of the Korean Society of Combustion, volume 2, issue 1, 1997, Pages 29~38
In this study, the experimental and numerical investigations of the ignition of methane-air mixtures by a electrically heated wire have been carried out. In order to define the initial condition and make the analysis simple, the following control unit was developed; which heats the wire to the setting temperature in a very short time, and maintains the wire temperature constant until ignition. Experiments with the feedback control have been performed using nickel and platinum wires in normal gravity and microgravity. From experimental results, ignition temperatures in normal gravity are higher than those in microgravity, however, the dependences of ignition temperature on equivalence ratio are not affected by natural convection. Numerical calculations, including catalytic reaction for platinum, have been performed to analyze the experimental results in microgravity. Numerical results show that reactants near platinum wire are consumed by catalytic reaction, therefore, the higher temperature is needed to ignite the mixture with platinum wire.
Modeling of Turbulent Molecular Mixing by the PDF Balance Method for Turbulent Reactive Flows
Moon, Hee-Jang ;
Journal of the Korean Society of Combustion, volume 2, issue 1, 1997, Pages 39~51
A review of probability density function(PDF) methodology and direct numerical simulation for the purpose of modeling turbulent combustion are presented in this study where particular attention is focused on the modeling problem of turbulent molecular mixing term appearing in PDF transport equation. Existing mixing models results were compared to those evaluated by direct numerical simulation in a turbulent premixed medium with finite rate chemistry in which the initial scalar field is composed of pockets of partially burnt gases to simulate autoignition. Two traditional mixing models, the least mean square estimations(LMSE) and Curl#s model are examined to see their prediction capability as well as their modeling approach. Test calculations report that the stochastically based Curl#s approach, though qualitatively demonstrates some unphysical behaviors, predicts scalar evolutions which are found to be in good agreement with statistical data of direct numerical simulation.