• Journal of the Korean Society of Combustion
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• v.15 no.1
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• pp.12-21
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• 2010

The main objective of this study was investigation of combustion instability characteristics in a lean partially premixed gas turbine dump combustor. Dynamic pressure transducers were located on combustor and inlet section to observe combustion pressure oscillation and difference at each measurement places. Also flame shape and $CH^*$ chemiluminescence were measured using a high speed ICCD camera. The combustor length was varied in order to have different acoustic characteristics from 800 to 1090 mm. The first section of this paper shows the stability map in model gas turbine combustor. And the effects of combustor length, mixture velocity in the mixing section and equivalence ratio were studied by the pressure perturbation and heat release oscillation. Also, the instability frequency and mode analysis were studied in last two sections. We observed two dominant instability frequencies in this study. Lower frequencies were obtained at lower equivalence ratio region and it was associated with a fundamental longitudinal mode of combustor length. Higher frequencies were observed in higher equivalence ratio conditions. It was related to secondary longitudinal mode of combustor and mixing section. In this instability characteristics, pressure oscillation of mixing section part was larger than pressure oscillation of combustor. As a result, combustion instability was strongly affected by acoustic characteristics of combustor and mixing section geometry.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.16-23
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• 2012

This study has been conducted to scrutinize agitation effects of an ultrasonic standing wave on the dynamic behavior of methane/air premixed flame. The propagating flame was caught by high-speed Schlieren images, through which local flame velocities of the moving front were analyzed in unprecedent detail. It is revealed that the propagation velocity agitated by the ultrasonic standing wave is greater than that without agitation at the stoichiometric ratio: the velocity enhancement diminishes as the equivalence ratio approaches upper flammability limit or lower flammability limit. Also, vertical locations of the wave-affected frontal distortions do not vary appreciably, unless the propagating-mode characteristics (pressure amplitude and driving frequency) of ultrasonic standing wave were not changed.

• Journal of the Korean Society of Combustion
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• v.22 no.1
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• pp.39-45
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• 2017

Combustion instability analysis of partially premixed model gas turbine combustor was conducted with 1D lumped method. Flame Transfer Function(FTF) was obtained with variation of fuel composition by Photo Multiplier Tube(PMT) and Hot Wire Anemometry(HWA). Decreasing instability frequency was observed when combustor length increased and multi-mode instability was confirmed. Instability frequency mode was changed while $H_2$ composition rate was increased and had agreement with experimental value. This work confirms that prediction of longitudinal combustion instability mode of partially premixed combustor is possible using 1D lumped method.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.261-266
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• 2003

An experimental study has been conducted to evaluate the effects of $CO_{2}$ on heat transfer from hydrogen oxygen-enriched flame. Experiments were performed on flames stabilized by a co-flow swirl burner, which mounted on top of the furnace. Five composition conditions of oxidizer were chosen with replacing $N_{2}$ with $CO_{2}$. In a steady state, total and radiative heat flux rates from the flame to the wall of furnace has been measured using heat flux meters. Temperature distribution in furnace also has been checked. Increasing $CO_{2}$ ratio in the oxidizer, the dominant heat transfer mode was changed into convection from radiation. Temperature in the furnace decreased but total heat flux increased.

• Journal of ILASS-Korea
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• v.25 no.3
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• pp.119-125
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• 2020

In this paper, we used Helmholtz solver based on 3D finite element method to quantitatively analyze the effects of change of gain, time delay and time delay spread, which are the main variables of flame transfer function, on combustion instability in gas turbine combustor. The effects of the variable of flame transfer function on the frequency and growth rate, which are the main results of combustion instability, were analyzed by applying the conventional heat release fluctuation model and modified one considering the time spread. The analysis results showed that the change of gain and time delay in the same resonance mode affected the frequency of the given resonance modes as well as growth rate of the feedback instability, however, the effect of time delay spread was not relatively remarkable, compared with the dominant effect of time delay.

• IE interfaces
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• v.25 no.4
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• pp.422-430
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• 2012

In this article, we introduced the estimation method by 'Safety Integrity Level'(SIL) for the criterion of safety assurance and performed a case study on a flame scanner. SIL requires probabilistic evaluation of each set of equipment used to reduce risk in a safety related system. FMEDA(Failure Modes, Effects and Diagnostic Analysis) method is widely used to evaluate the safety levels and provides information on the failure rates and failure mode distributions necessary to calculate a diagnostic coverage factor for a part or a component. Basically, two parameters resulting from FMEDA are used for SIL classification of the device : SFF(Safe Failure Fraction) and PFD(Probability of Failure on Demand). In this case study, it is concluded that the flame scanner is designed to fulfill the condition of SIL 3 in the aspect of SFF and PFD.

• Journal of the Korean Society of Combustion
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• v.11 no.3
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• pp.18-25
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• 2006

The present studying is aimed to establish the relationship between flame chemiluminescence$(OH^*,\;CH^*,\;C_2^*)$ intensities and combustion conditions such as $NO_x$ emission characteristics. Measurements are made for $OH^*,\;CH^*,\;C_2^*$ radicals in gas & light oil diffusion flames. At turbulent nonpremixed combustion mode, the equivalence ratio is varied. The optical emissions were measured by photomultiplier(PMT) using optical band pass filter and spectrometer system. The experimental results showed that the ratio of radicals and $NO_x$ emission characteristics have exponential correlations and equivalence ratio characteristics have linear correlations at this experimental conditions.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.132-137
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• 2005

The burning characteristics of interacting spherical droplet in a turbulent flow are numerically investigated. The transient combustion of 3-dimensionally arranged droplets, both the fixed streamwise droplet distances of 3 radii and 10 radii and different turbulence intensities, is studied. The results obtained from the present numerical analysis show that droplet vaporization rate for heptane droplet is insensitive to turbulence intensity, and that the transient flame configuration and retardation of droplet surface temperature augmentation with streamwise droplet spacing substantially influence vaporization process of interacting droplets. Single flame mode in which individual flames are merged into single flame, with decreasing streamwise droplet spacing, becomes faster. Therefore, vaporization rate of the second droplet with decreasing streamwise droplet spacing decreases remarkably with flame movement.

• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.524-529
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• 2000

Silica slab wavegudie was fabricated on Si substrates by FHD for planar optical passive devices. The slab waveguide consists of lower clad and core layers, where core layer index is controlled by GeO2 addition. Doping of GeO2 in silica is difficult because of the low deposition density due to nonspherical particle generation in FHD process. Silica core particles deposited at various conditions such as flame temperature and substrate scanning were analyzed by SEM and TEM. As the flame temperature increased, the surface roughness of the core layer was decreased up to 3.6 nm after consolidation. Index difference and thickness of core of slab waveguide were 0.3%, 8$\mu\textrm{m}$ respectively. Measured optical loss at TE mode was <0.04 dB/cm at 1.3$\mu\textrm{m}$ and <0.06 dB/cm at 1.55$\mu\textrm{m}$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.548-558
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• 1995

An experimental investigation has been conducted to study the spray and combustion characteristics using the air-assisted twin fluid atomizer. Axial mean and fluctuating velocity components as well as drop-size distributions in non-reaction spray were measured with a nonintrusive phase doppler technique. Droplet number density distributions were also visualized using high speed CCD camera. Locations of spray and flame boundaries are obtained by direct photographic method. It is confirmed that at the fixed fuel flow rate, the increase of the atomizing air flow causes improvements on both spray and combustion characteristics under stable flame conditions. Internal group combustion modes where flame is located inside the spray boundary are observed to exist in the upstream region of higher droplet number density.