• Journal of the Korean Society of Combustion
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• v.17 no.4
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• pp.11-20
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• 2012

The Blow-off characteristics of LPG/air lean pre-mixed flames were experimentally investigated using a double and a multiple concentric coflow burners. Experiments were conducted to understand the effects of recirculation motion, thermal interaction between flames, and stratified flame configuration. Here, the stratified premixed flame is a "new concept" of a flame that sequentially contains fuel rich, stoichiometric, and fuel lean reaction zones in a flame. The blow-off from a lean premixed flame was significantly suppressed with recirculation motion. The recirculation motion by itself, however, was not sufficient to prevent the blow-off when the equivalence ratio became low. The existence of a inner premixed flame could also help to prevent the blow-off of lean premixed flame; however, the blow-off suppression effect was rather diminished by weakened recirculation motion with the presence of inner flame. The inner flame could be separated from an outer flame on a multiple concentric coflow burner, causing recirculation motion as well as thermal interaction between flames to become effective; therefore, the blow-off was further suppressed. The lean premixed flame could be stabilized with a fuel rich premixed flames that was produced with the supply of fuel through an inner nozzle. The penetration of lean premixed gas from outside into the fuel stream produced a lifted rich premixed flame. Chemiluminescence images of OH, CH, and $C_2$ radicals confirmed the structure of a stratified premixed flame. The stable premixed flames could be obtained at the very fuel lean condition by applying the stratified premixed flame concept.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.853-858
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• 2001

The knowledge of flame structure is essential for control of combustion instability phenomena. Some results of an experimental study on mechanism of naturally occurring combustion oscillations with a single dominant frequency are presented. Tests were conducted in a laboratory-scale dump combustor at atmospheric pressure. Sound level meter was used to track the pressure wave inside the combustor. The observed instability was a longitudinal mode with a frequency of $\sim341.8Hz$. Instability map was obtained at the condition of inlet temperature of $360^{\circ}C$, mean velocities of $8.5\sim10.8m/s$ and well premixed mixture. It showed that combustion instability was susceptible to occur in the lean conditions. In this study, unstable flame was observed from stoichiometric to 0.7 in overall equivalence ratio. At selected unstable conditions, phase-resolved OH chemiluminescence images were captured to investigate flame structure with various mean velocities. As mean velocity is increased, the flame grows and global heat release was changed. Due to these effects, combustion instability can be maintained at more lean air-fuel ratio. Also, these results give an insight to the controlling mechanism for an increasing heat release at maximum pressure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.608-611
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• 2011

Laser-induced combustions and explosions generated by high laser irradiances were explored by Laser-Induced Breakdown Spectroscopy (LIBS) in rich, and stoichiometric conditions. The laser used for target ablation is a Q-switched Nd:YAG laser with 7 ns pulse duration at wavelength of 1064 nm laser energies from 40 mJ to 2500 mJ ($6.88{\times}10^{10}-6.53{\times}10^{11}\;W/cm^2$). The plasma light source from aluminum detected by the echelle grating spectrometer and coupled to the gated ICCD(a resolution (${\lambda}/{\Delta}{\lambda}$) of 5000). This spectroscopic study has been investigated for obtaining both the atomic signals of aluminum (fuel) - oxygen (oxidizer) and the calculated ambient condition (plasma temperature and electron density). The essence of the paper is observing specific electron density ratio which can support the processes of combustion and explosion between ablated aluminum plume and oxygen from air by inducing high power laser.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.548-555
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• 2017

This study investigated the influence of air staging on combustion and NOx emission in a tangential-firing boiler at a 560 MWe capacity. For air staging, the stoichiometric ratio (SR) for the burner zone was varied from 0.995 to 0.94 while the overall value was fixed at 1.2. The temperature and heat flux in the burner zone and upper furnace corresponded to the distribution of SR, while the total boiler efficiency remained similar. The NOx emission at the furnace exit was reduced by up to 20% when the SR in the burner zone decreased to 0.94. However, the amount of unburned carbon and slagging propensity was not noticeably influenced by the changes in the SR of the burner zone. Therefore, it was favorable to lower the SR of the burner zone for reduction of NOx emission.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.711-721
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• 2005

In order to design of emergency ventilation systems, the smoke movements in tunnel fire with natural and forced ventilation were investigated. Reduced-scale experiments were carried out under the Froude scaling with novel fire source consisting many wicks. Temperature profiles were measured under the ceiling and vertical direction along the center of the tunnel and poisonous gases were measured at emergency exit point in the natural ventilation case. In forced ventilation, temperature profiles were measured with various flow rate to obtain critical velocity. The results showed that the interval of emergency exit having 225m was estimated reasonably through the measurements of temperature variation and poisonous gas in the natural ventilation. In the case of forced ventilation, the temperature distribution near fire source is remarkably different from that of natural ventilation. Also, the critical velocity to prevent upstream smoke flow has the range of 0.57m/s between 0.64m/s. Finally, it was also identified that although the increase of flow rate can suppress the backward flow of smoke to upstream direction, brings about the increase of flame intensity near stoichiometric fuel/air ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.83-90
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• 2016

Ramjet mode combustion test was performed for a dual-mode ramjet engine model. The engine model consists of an air intake, a combustor and a nozzle. The combustor in the model has a large backward-facing step, designed to be used as a part of a rocket-based combined cycle engine. The test was performed at the flight speed of Mach 5 and the altitude of 24 km. Strong combustion was established only when the fuel was injected from both of the bottom-side and cowl-side wall. When the total fuel stoichiometric ratio was 1.0, distributed as 0.5 on the cowl side and 0.5 on the bottom side, the flow became subsonic at some portion in the combustor by thermal choking, i.e., ramjet mode was established for this condition.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.301-305
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• 2007

The performance of polymer electrolyte membrane fuel cell could be decreased due to coolant leaked from connection part. Micro pump was used to put small amount of coolant and investigate the effect on fuel cell. The stoichiometric ratio of hydrogen/air was 1.5/2.0, both side of gas was fully humidified, and current density of $400mA/cm^2$ was used as standard condition in this experiment. Constant current method was used to check performance recovery from coolant effect in 3 cell stack. The performance was recovered when coolant was injected in cathode side. On the other hand, the performance was not recovered when coolant was injected in anode side. Ethylene glycol could be converted to CO in oxidation process and cause poisoning effect on platinum catalyst or be adhered on GDL and cause gas diffusion block effect resulting performance decrease. Water with nitrogen gas was supplied in anode side to check performance recovery. Polarization curve, cyclic voltammetry, electrochemical impedance spectroscopy was used to check performance, and gas chromatography was used to check coolant concentration. Constant current method was not enough in full recovery of performance. However, water injection method was proved good method in full recovery of performance.