• Journal of the Korean Society of Combustion
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• v.21 no.2
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• pp.15-21
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• 2016

Flame characteristics and combustion stability of a swirl coaxial injector are studied experimentally. Characteristics of flame and combustion instability are analyzed with the parameter of MFR (momentum flux ratio) using hexane instead of kerosene. Flame patterns of blue and yellow are changed with variable MFR. Combustion instabilities are measured and analyzed by adopting a model chamber. Combustion instability mapping is made by evaluating damping factor at the 2 L (second longitudinal) mode with variable MFR in 63 cases for operating condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.343-349
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• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral flame size was less than burner nozzle diameter and thus lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The oscillation is the direct outcome from the advancing and retreating edge flame. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which can be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).

• Journal of the Korean Society of Combustion
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• v.14 no.4
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• pp.7-16
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• 2009

Porous metal plates (Metal fiber, muti-hole metal plate) using mainly in surface burner are known to have a corrosion and durability problem under high temperature condition. In this study, premixed flat flame with perforated ceramic tile of more durable cordierite material was examined with respect to combustion stability and emission. The flat premixed ceramic burner consists of perforated ceramic tile and various type of baffle plates to form stable surface flame. The results show that most stable flat flame is generated using baffle plate with open ratio of 0.193. In downward flat flame mode which is widely used in condensing boiler, CO is measured below 50ppm from equivalence ratio 0.755 to 0.765 and $NO_X$ is measured below 12ppm from equivalence ratio 0.75 to 0.79. It is also found that the range of blue flame in flame stability curve becomes wider with increasing heat capacity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.425-432
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• 2004

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence(OH$\^$*/) image and its Abel inverted image to investigate the flame structure at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure and NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ∼341.8㎐, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between OH$\^$*/ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.79-82
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• 2009

Unsteady numerical analysis of an entire supersonic propulsion system from intake to nozzle was performed to study dynamic interaction between terminal shock in the intake and flame in the combustor. Both acceleration and cruise flight-modes were considered. Acoustic mode of the entire engine for both flight-modes were investigated by detail analysis of pressure fluctuation at each location of engine.

• Journal of the Korean Institute of Gas
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• v.11 no.1 s.34
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• pp.1-8
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• 2007

The purpose of this study is to conduct a survey of the flame stability range and the emission characteristics for the optimum design of turbulent premixed flat burner. For that, the flame stability range was selected by the direct photography of the flame. And the mean temperature and CO, HC, $CO_{2}\;and\;O_{2}$ concentration distributions by changing the excess air ratio were measured. As results of this study, the flame stability range turned out to be getting narrower as fuel flow was increased. The blue flame mode was more excellent than any other flame modes in the emission characteristics by excess air ratio change. And the emission characteristics by fuel flow change were best at fuel flow 1l/min. Also, we found combustion noise during experiment of flame stability range. It had nothing do with excess air ratio range.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.86-91
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• 2007

A study was performed to understand self-excited pressure fluctuations in the lean premixed flames and to evaluate the effect of Helmholtz resonator on the pressure fluctuations. As low-frequency pressure fluctuations have been reported to cause fatal damage to the combustor and the entire system, Helmholtz-type resonators, which reduce the damage by low-frequency pressure fluctuation in the combustor, are attached to the channel of unburned mixture flow. It is found that the range of low-frequency pressure fluctuations of flame mode 2 is narrowed by the attachment of Helmholtz resonators. From this result, if Helmholtz-type resonators are applied to actual gas turbine combustor, it is confirmed that Helmholtz resonators attached on the fuel discharge hole are also effective for narrowing the range of flame mode 2

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1081-1092
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• 2004

The synthesis of Ni-catalyzed multi-walled carbon nanotubes and nanofibers on a catalytic metal substrate, using an ethylene fueled inverse diffusion flame as a heat source, was investigated. When the gas temperature was varied from 1,400K to 900K, approximately, carbon nanotubes with diameters of 20∼60nm were formed on the substrate. In the regions where the gas temperature was higher than 1,400K or lower than 900K, iron nanorods or carbon nanofibers were synthesized, respectively. Based on the quantitative analyses of large amount of SEM and TEM images, the nanotubes formed closer to the flame had a tendency of having larger diameters. HR-TEM images and Raman spectra revealed that carbon nanotubes synthesized had multi-walled structures with some defective graphite layers at the wall. Based on the graphite mode of the Raman spectra, it was believed that the optimal synthesis could be obtained as the substrate was positioned at between 5.5mm and 5.0mm, from the flame axis.

• Journal of the Korean Society of Combustion
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• v.22 no.2
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• pp.1-8
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• 2017

To evaluate the combustion instability of a gas turbine combustor, the DMD technique was applied. The mode frequency results for each fuel composition were compared with FFT(Fast Fourier Transform) results. The damping coefficient, which is a quantitative parameter for combustion instability, was evaluated for 5 experimental cases. The flame transfer function (FTF) was calculated in the most unstable test case. In deriving the FTF, gain and phase were calculated using DMD technique. As a result of the analysis of the OH radical perturbation of the DMD, the heat release fluctuation was the highest at 100 Hz, at which the highest value of gain is observed. The frequency of FFT and FTF were different. In order to clarify the reason for this, FTF for various resonance frequencies was performed and it shows that the pattern of gain was similar to FFT.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.59-60
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• 2017

Combustion instability of gas turbine is performed by adopting dynamic mode decomposition (DMD). The unstable frequencies are calculated and compared with FFT results. The damping coefficient derived from the DMD technique and FFT results were compared and analyzed. OH radical is measured by experimental work and fluctuation field is extracted and FTF was calculated at various points with DMD. The gains of FTF are changed depending on the extraction position of the heat release fluctuation field.