• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.69-75
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• 2007

In this study, the difference of flame stability zone for natural gases from producing districts was studied experimentally using a new type of flame stability diagram. The similarity of stable flame zone between a domestic appliance and an interchangeability test(IT) burner is also examined. As a result, the stable flame zones expressed by limits curves of flame lifting and yellow tipping show the similar results in a domestic gas range and IT burner. Furthermore, IT burner can reproduce the flash back phenomena and show the distinct difference of fuel type as the burner diameter is increased. To suggest the new type of flame stability diagram in the respect of fuel interchangeability, the air flowrate and Wobbe fuel flowrate were adopted as axis coordinates. It can be identified that the new diagram can provide the useful information on the difference of flame stability zone, heat input rate and air-fuel ratio when a fuel is altered to other fuels under the identical operating conditions. Finally, the stable flame zones for natural gas of 6 type are compared, and the detailed information to use as the interchangeability fuels of standard natural gas is provided using the new type of flame stability diagram.

• Journal of the Korean Society of Combustion
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• v.15 no.3
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• pp.1-7
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• 2010

Edge flames have been interested as a basic structure that is concerned to flame stabilization and re-ignition of non-premixed flames. The edge flame consists of a lean premixed flame, a rich premixed flame, and a diffusion flame. In order to investigate fundamental structures of the edge flames at the conditions near the flammability limits, edge flames were stabilized within a heated narrow channel. Highly diluted partially premixed methane was used, and the flow rates of air and the partially premixed mixture were controlled. Various flame behaviors, including a transition between ordinary edge flames and premixed flames, were observed. Flame stabilization characteristics were examined as well. All flame stabilization conditions in this study showed a similar trend: characteristic time scales were inversely proportional to the equivalence ratio defined at the burner inlet. Finally, an interesting flame structure having a weak diffusion branch enveloped by a closed premixed branch was found near the flammability limits even in a fuel-air mixing layer. This structure was named as a "flame-drop" and the importance of this structure was first suggested.

• Journal of the Korean Society of Combustion
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• v.13 no.3
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• pp.1-8
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• 2008

A flame stability diagram in a partially premixed flame is typically expressed using the axis coordinates of heat input rate and equivalence ratio. These diagrams are inadequate for identifying changes in combustion conditions and flame stability when a reference fuel is substituted with other fuels under identical operating conditions. This study proposes a new type of diagram and validates it experimentally. In this new diagram, the axis coordinates are air flow rate and Wobbe fuel flow rate, defined as the fuel flow rate multiplied by the square root of the relative density. The diagram was validated in trials using various fuels, including $CH_4$, $C_{3}H_{8}$, and LFG-$C_{3}H_{8}$ mixed fuels, in a domestic gas-range and an gas interchangeability test burner. The results of these trials show that the new diagram can provide information useful for assessing gas interchangeability of combustion conditions and flame stability when one fuel is substituted with another under identical operating conditions.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.23-30
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• 2008

An analytical expression for the turbulent burning velocity is derived from the asymptotic zone conditional transport equation at the leading edge. It is given as a sum of laminar and turbulent contributions, the latter of which is given as a product of turbulent diffusivity in unburned gas and inverse scale of wrinkling at the leading edge. It was previously shown that the inverse scale is equal to four times the maximum flame surface density in the wrinkled flamelet regime [1]. The linear behavior between $U_T$ and u' shows deviation with the inverse scale decreasing due to the effect of a finite flamelet thickness at higher turbulent intensities. DNS results show that $U_T/S^0_{Lu}$ may be given as a function of two dimensionless parameters, $u'/S^0_{Lu}$ and $l_t/\delta_F$, which may be transformed into another relationship in terms of $u'/S^0_{Lu}$, and Ka. A larger $l_t/{\delta}_F$ or a smaller Ka leads to a smaller scale of wrinkling, hence a larger turbulent burning velocity in the limited range of $u'/S^0_{Lu}$. Good agreement is achieved between the analytical expression and the turbulent burning velocities from DNS in both wrinkled and thickened-wrinkled flame regimes.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.58-62
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• 2005

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor were investigated using CFD and Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach 0.3 at inlet. The computational and experimental results showed that the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation regions are increased with approaching closer to the center of the combustor. Since the performance of combustor is closely dependent not only on the main recirculation in the dome region but also on the secondary recirculation flow in a junction region, the optimal angle of the air intakes should be considered the recirculation size as frame holder.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.115-120
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• 2003

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor are investigated using CFD and 3-D Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach0.3 at inlet. Both computational and experimental results showed the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation region increased with upon closer center of axial combustor. Since the performance of combustor depends on not only the main recirculation in the dome region but also the secondary recirculation flow in a junction region, the optimal angle of the air intakes should consider the recirculation size as frame holder.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.43-53
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• 2000

Experimental studies on determination of the supply leading time of propellants to combustion chamber have been made to stably and efficiently guarantee the ignition process with liquid rocket engine. The propellant used is a Jet A-1 as fuel and a liquid oxygen as oxidizer. Unlike impinging FOOF type of injectors are arranged radially and the designed O/F ratio is 2.34. The present experiment program also includes the stability on the quadlet type of ignitor using the triethylalumimum as an ignition source and injector life tests. Experimental results clarifies that the propellant supply through LOx leading to combustion chamber is proper for stable ignition and combustion processes based on the fuel and oxidizer manifold pressures, combustion chamber pressure, and the variation of flame length from the nozzle exit with lapse time, and shows that the leading supply time of propellants affects the engine performance little. The effect of positioning cooling holes is remarkable to protect the injector face.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.123-129
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• 1998

A numerical study has been conducted to investigate the effect of shock waves on the mixing and the recirculation zone of a hydrogen jet diffusion flame in a supersonic combustor. The general trends are compared with the experimental results obtained from the supersonic combustor at the University of Michigan. For the numerical simulation of supersonic diffusion flames, multi-species Navier-Stokes equations and detailed chemistry reaction equations of $H_2$-Air are considered. The $K-{\omega}/k-{\varepsilon}$ blended two equation turbulent model is used. Roe's FDS method and MUSCL method are used for convection fluxes in governing equations. Numerical results show that when slender wedges are mounted at the combustor wall the mixing and the combustion are enhanced and the size of recirculation zone is increased . The flame shape of supersonic flames is different in the flame-tip; it is not closed but open. The flame shape is shown to be greatly affected by shock waves.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.83-86
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• 2003

The chemical laser system makes use of a diffusion type chemical reaction, so a fuel is separated from an oxidant by some gap, which is base in this system. In this study, the effects of base on the population inversion that is one of the most important things in the chemical laser system are numerically investigated. The results are discussed by comparison with three cases of base sizes; 0.4mm, 0.8mm and 1.6mm. Major results reveal that the range of population inversion also increases almost linearly in the transitions; DF$^{(2)}$ -DF$^{(1)}$ and DF$^{(3)}$ -DF$^{(2)}$ as the length of base becomes longer.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.447-450
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• 2010

This study was conducted to explore the flow contamination in the $CH_4-O_2$ vitiated air heater. Non-equilibrium and equilibrium calculation were made of the flow processes in the heater and nozzle assuming the inviscid and one dimensional flow. The results were compared with the measurement data. The overall results of this study showed additional non-equilibrium calculation should be considered to assess the presence of NO, which species could yield the combustion delay or no reaction, as a contaminant.