• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.105-112
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• 2002

The objective of this research is to determine generally applicable design principles for the development of internally staged combustion devices. Utilizing a triple annulus combustor, air staged commercial propane flame configuration are studied. For this triple air staged combustor, the angular momentum weighted by it's swirl number and air distribution ratio was observed to be the critical criteria. An internal recirculation zone which develops on the centerline of the flame immediately downstream of the burner entraps the fuel into a fuel rich eddy. Then sufficient heat must he transferred from the flame via radiation to the chamber heat transfer surfaces, such that when the second air is introduced, peak flame temperatures are suppressed. It is experimentally found out that the total NOx emission level in this type of burner is lower than 0.75g/kg.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.78-85
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• 2000

The transient laminar reacting flows around fuel droplet have been numerically analyzed. The physical models used in this study can account for the variable thermophysical properties and the chemistry is represent by the one-step global reaction model. The present study is focused on the vaporization and ignition characteristics, flame structure including wake flame, transition flame and envelope flame, and interaction between droplets. special emphasis is given to the triple flame structure and flame stabilization.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.170-177
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• 2005

The fuel-lean premixed flame has been considered one of the most efficient ways to reduce $NO_X$ emission during a combustion process. However, it is difficult to achieve stable fuel-lean premixed flames over the wide range of equivalence ratios: therefore, the application of fuel-lean flames to a practical combustion system is rather limited. In this study, the stability characteristics of fuel-lean flames stabilized by fuel-rich flames are investigated experimentally using a slot burner as a part of the basic research for practical application such as lean burn engines. Spontaneous emission of radical species were examined to understand the stability mechanisms of rich-lean premixed flames. The presence of fuel-rich flames could significantly lower the lean limit of fuel-lean flames. The stability of a fuel-lean flame is enhanced with the increase of fuel flow rate in a fuel-rich flame; how ever, it is not sensitive to the equivalence ratio of fuel-rich flames in the range of 1.2-2.4. The mechanisms of stable rich-lean premixed flames could be understood based on the characteristics of triple flame.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.19-25
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• 2015

An experimental study was conducted to find the effect of a pilot flame on the flammability of inert-gas-diluted methane and propane. The diffusion pilot flame was formed with propane at the innermost nozzle of a concentric triple co-flow burner. The main diffusion flame was formed with nitrogen-diluted methane or propane at the outermost nozzle of the burner. An air flow was located in-between. The results showed that the existence of the pilot flame helped stabilizing the main flame even at the flammability limit concentration of nitrogen-diluted fuel. The co-flow burner generated re-circulation zones and local variation of equivalence ratio depending on the flow rates of the reactants, which are known to help flame stabilization. Hot-wire experiments confirmed that both heating of the reactants and supplying of active chemical species by the pilot flame contributed to stabilization of the main flame. The results of this study would suggest a design concept for an efficient SVRU system that minimizes the emission of unburned hydrocarbon fuel from ship fuel tanks.

• Journal of the Korean Society of Combustion
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• v.8 no.1
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• pp.25-35
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• 2003

The objective of this research is to determine generally applicable design principles for the development of internally staged combustion devices. Utilizing a triple annulus combustor, the detailed combustion characteristics are studied. For this triple air staged combustor, the angular momentum weighted by it#s swirl number and air distribution ratio was observed to be the critical criteria of NOx emission. An internal recirculation zone which develops on the centerline of the flame immediately downstream of the burner entraps the fuel into a fuel rich eddy. Then sufficient heat must be transferred from the flame via radiation to the chamber heat transfer surfaces, such that the peak flame temperatures are suppressed when the second air is introduced. It is experimentally found out that the total NOx emission level in this type of burner is below 50ppm(3% Ref. O2) at optimum operating conditions.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.3
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• pp.321-328
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• 2022

The current development tend of the gun propellants that they should have low sensitivity and high energy. We studied a nitrocellulose based propellant composition that replaced sensitive NG with RDX and DEGDN which high energy and low sensitivity. The important factors in the design of the gun propellant were impetus and flame temperature. NC-based propellant containing RDX showed similar impetus but low flame temperature compared to KM30A1, a triple-based propellant. The developed propellant composition didn't show any abnormal combustion reaction and the characteristics of ballistic resistance were also confirmed.

• Journal of the Korean Society of Combustion
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• v.7 no.2
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• pp.1-6
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• 2002

Characteristics of laminar lifted flames of propane highly-diluted with nitrogen have been investigated at various temperatures of coflow air. At various fuel mole fractions, the base of laminar lifted flames has the structure of tribrachial (or triple) flame. The liftoff heights are correlated well with the stoichiometric laminar burning velocity considering initial temperature at a given coflow velocity. It shows that lifted flames are stabilized on the basis of the balance mechanism between local flow velocity and the propagation speed of tribrachial flame, regardless of the temperature of coflow and fuel mole fraction. Lifted flames exist for a jet velocity even smaller than the stoichiometric laminar burning velocity, and liftoff velocity increases more rapidly than stoichiometric laminar burning velocity as coflow temperature increases. These can be attributed to the buoyancy effect due to the density difference.

• 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.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1710-1718
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• 2002

The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.

• Journal of the Korean Society of Safety
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• v.11 no.3
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• pp.66-74
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• 1996

Numerical simulations were carried out using standard Reynolds stress turbulence model(LRR model) and modified RSM(Janicka model ) to validate these models in combustion flow fields. Two flames were selected for use as a benchmark data for model testing. One is a conventional jet diffusion flame that has the effect of suppression of turbulence by combustion. The other is a triple jet diffusion flame that designed to give high turbulence to the periphery of the flame and to remove the low Reynolds-number flow fields. As a result, it was found that the modification of standard RSM model is indispensable in the modelling of flames with low turbulence region. And it is also necessary to improve the existing modified models for the universal use.