• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

• Fire Science and Engineering
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• v.23 no.3
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• pp.73-78
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• 2009

The fire whirl occurring in the urban and/or wildland fire is generated by the instabilities of atmosphere. The fire whirl is a rare phenomenon, but highly destructive because it has high inhalation and lift force. In this study, experimental and numerical studies are performed with oriental oak leaves, for investigating of the fire whirl characteristics occurred in wildland fire. As a result of experiment, the circulation intensity increases as the induced air speed increases, then the heat release rate and flame height increase 22.8%, 18.4% compared with open fire in highest circulation. Furthermore the numerical results shows same trend with the experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.259-267
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• 2010

In this study, the effect of particle size on the combustion characteristics of pulverized sub-bituminous coal was experimentally investigated. A laminar-flow-entrained reactor was designed and implemented to realize the desired heating ratio and temperature corresponding to the combustion atmosphere of a pulverized-coal-fueled furnace. The flame length and structure of burning particles according to different sizes were investigated. Coal combustion processes were clearly distinguished by direct visual observation of the flame structure. The onset point of volatile ignition is greatly affected by changes in the particle size, and the burning time of the volatiles is least affected by changes in the particle size. The length and instability of char flame also increase with the increase of the particle size. However, the char consumption rate within the residential time remains nearly constant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.933-938
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• 2011

In this study, the heat transfer characteristics and NOx and CO emissions of a heat exchanger were investigated using a premixed burner. The experiments involved changing the distance between the burner and heat exchanger to 30, 40, and 50 mm with various equivalence ratios. The results showed that the NOx and CO emissions increased as the equivalence ratio was increased because the flame temperature increased, regardless of the distance between the burner and heat exchanger. In particular, the CO emission increased significantly as the distance between the burner and heat exchanger was decreased. The optimal equivalence ratio for the A-type heat exchanger (distance between the burner and heat exchanger: 30 cm) was 0.7 in the experimental range. In this case, the CO and NOx emissions were 94.5 ppm and 11.2 ppm, respectively, and the efficiency was 84.1%.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.65-70
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• 2012

Experimental investigations were carried out to examine the explosion characteristics by different sizes in the wall surface shape of a water gel barrier in an explosion chamber, 1,600 mm in length with a square cross-section of $100{\times}100\;mm^2$. The sizes in the wall surface shape were varied by using water gel barriers with a cross-section of $100{\times}200\;mm^2$ and its were varied in the bottom of the chamber away 300, 700 and 1,100 mm, respectively from the closed end of the chamber. The flame propagation images were photographed with a high speed camera and the pressure was recorded using a pressure transducer and a data acquisition system. It was found that as the size of the wall surface shape increased, the flame propagation process and the time taken to reach the maximum pressure were found to be faster. As a result, both the flame speed and the explosion overpressure increased as the size of the wall surface shape increased.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.35-40
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• 2006

The combustion instability in a model dump combustor with an exhaust nozzle and the possibility of combustion control using a loudspeaker to these instabilities were studied. By changing inlet velocity, combustor length and equivalence ratio, dynamic pressure signals and flame structures were simultaneously taken. Because inlet velocity and combustor length affect the life time of vortex in the dump combustor, the results showed that as the combustor length increased and the inlet velocity decreased, the instability frequency decreased and the maximum power spectral density of the dynamic pressure generally decreased. Also, instability frequency and maximum power spectral density of the dynamic pressure increased with the increment of equivalence ratio. From the data of close-loop control, the optimum time-delay control using a loudspeaker was confirmed to be able to reduce the vortex shedding induced from the mixed acoustic-convective mode combustion instability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.48-58
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• 2006

The spray and combustion characteristics of liquid jet in cross flow with variation of injection angle are numerically studied. Numerical analysis was carried out using KIVA code, which may be used to generate numerical solutions to spray and chemical reactive fluid problem in three space dimensions and modified to be suitable for simulating liquid jet ejected into the cross flow. Wave model and Kelvin- Helmholtz(KH) /Rayleigh-Taylor(RT) hybrid model were used for the purpose of analyzing liquid column, ligament, and the breakup of droplet. Penetration length increases as flow velocity decreases and injection velocity increases. Numerical error increases as inflow velocity increases. The results of flame propagation contour in combustion chamber and local temperature distribution, combustion emissions were obtained.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.71-78
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• 2002

Experiments have been performed using two-color PIV in hydrogen non-premixed flames with various conditions of coaxial air, which was classified into three cases with/without reaction. Mean velocity, turbulence intensity and Reynolds stress were analyzed using flow fields from PIV measurement First, the similarity of pure jet had a good agreement with previous results of other researchers. It was found that the decay of centerline velocity was proportional to $x^{-1}$ in coaxial air conditions. By normalizing axial distance with effective jet diameter defined by effective density, the data of centerline velocity collapsed a single line. And the radial profiles of mean velocity showed that they didn't become self-similar because the curves differed from each other as coaxial air velocity increased at fixed fuel velocity. Also, turbulence intensity became self-similar further downstream than mean velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.179-188
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• 2011

Experiments were conducted in a constant-pressure combustion chamber to investigate the effects of hydrocarbon addition on cellular instabilities of syngas-air flames. The measured laminar burning velocities were compared with the predicted results computed using reliable kinetic mechanisms with detailed transport and chemistry. The cellular instabilities that included hydrodynamic and diffusional-thermal instabilities of the hydrocarbon-added syngas-air flames were identified and evaluated. Further, experimentally measured critical Peclet numbers for fuel-lean flames were compared with the predicted results. Experimental results showed that the laminar burning velocities decreased significantly with an increase in the amount of hydrocarbon added in the reactant mixtures. With addition of propane and butane, the propensity for cell formation was significantly diminished whereas the cellular instabilities for methane-added syngas-air flames were not suppressed.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.253-254
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• 2014

지구온난화 문제는 한국가의 문제가 아니라 인류의 문제로 대두되어 많은 이에대한 많은 연구가 이루어 지고 있다. 지구온난화의 주 대상물질인 화석연료로부터 연소시 발생하는 이산화탄소를 감축하기위한 많은 규제와 노력이 요구된다. CCS(Carbon Capture & Storage)란 화석연료로 부터 연소시 대기 중으로 배출되는 온실가스($CO_2$)를 포집하여 재생 또는 지중, 해양에 저장하는 기술로서 국가녹색성장 핵심기술중의 하나로 분류되며, $CO_2$ 회수방안, 저장, 처리관련 연구를 비롯하여 국내외 적으로 활발한 연구가 이루어 지고 있다. 또한 순산소 연소기술을 통한 $CO_2$ 회수, 처리기술은 연료의 산화제를 공기대신 순도 95% 이상의 고농도 산소를 이용하여 순산소연소를 하며, 이때 발생하는 배가스의 대부분은 $CO_2$와 수증기로 구성되어 있다. 발생된 배가스의 약 70~80%를 다시 연소실로 재순환시켜 연소기의 열적 특성에 적절한 연소가 가능하도록 최적화함과 동시에 배가스의 $CO_2$ 농도를 80% 이상으로 농축시켜 회수를 용이하게 하며, 동시에 공해물질은 NOx 발생량을 10ppM 이하로 줄일 수 있는 기술이다. 천연가스를 생산하는 LNG기지에서 연소에 의한 이산화탄소를 발생시키는 기기로는 수중연소식기화기(SMV ; Submerged Combustion Vaporizer)를 들 수 있다. SMV는 버너를 이용하여 $-162^{\circ}C$ LNG를 $10^{\circ}C$의 LN로 기화시키는 설비로서 특히 동절기에 작동시키며 $CO_2$를 배출시키는 연소기다. 본 연구에서는 수중연소식 SMV에 순산소 연소방식을 적용하여 천연가스와 산소를 연소시키므로서 발생되는 $CO_2$를 LNG냉열을 이용 액체화 시켜 회수하는 연구를 수행하고 있다. 내용중에 수중연 소식 SMV에 대한 순산소 연소기를 개발하는 연구를 수행하였으며, 실제 SMV의 1/10크기, 열량기준 1/900로 모형을 제작하여 실험하였다. 연소기 노즐 은 직경 0.6mm, 배가스가 수조내에서 48개의 노즐을 제작하였다. 실험결과 일정량 이상의 $CO_2$ EGR율이 일정 값 이상이 되면 화염의 길이가 공기/NG 화염 길이와 큰 차이가 없었으며 $CO_2$ EGR율이 100%이상에서는 $CO_2$ EGR율 증가에 따른 화염길이 변화는 크게 나타나지 않았다. CO 배출 농도는 공기/NG 연소의 경우보다 높게 나타났으며, ${\lambda}$가 1.4보다 높은 조건에서는 측정되지 않았다. NOx의 배출 농도는 약 1~8ppm으로 나타났다.