• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.7-14
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• 2003

Exhaust Gas Recirculation (EGR) system is used to reduce NOx emission, to improve fuel economy, and to suppress knock since it offers the benefits of the inlet charge dilution. The effects of EGR was investigated on the performance and emission to reduce exhaust thermal load with a single cylinder liquid-phase LPG injection engine, in a wide range of EGR rate, engine conditions and LPG proportions. As EGR rate was increased, NOx was reduced while HC was increased. Pumping loss reduction by EGR improved bsfc and increased EGR lowered exhaust gas temperature. And, LPG proportions were made a difference on the performance and emission characteristics.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2540-2545
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• 2007

A computational study of BLDC motor is presented to elucidate thermo-flow characteristics in winding and bearing with heat generation. Rotation of rotor and blades drives influx of ambient air into the rotor inlet and the inflow rates are predicted more at the front-side inlet than at the rear-side, which can be ascribed to the different pressure distribution. Recirculation zone appears in the tiny interfaces between windings, however, showing the enhanced cooling performance due to the higher velocity distribution near the rotor wall. In contrast, flow separation and incline angle of bearing groove, and relatively slower velocity distribution cause poor cooling performance and therefore the redesign of the bearing groove is significantly required.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.223-228
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• 1997

The gas dynamics in a stagnation point upflow OMVPE reactor were studied by Raman spectroscopy. The gas temperature was measured as a function of inlet gas velocity and aspect ratio for both H$_2$ and N$_2$ carrier gases. The centerline temperature gradient was latger at higher inlet velocities and with the use of N$_2$, and only weakly dependent on the aspect ratio. a tracer molecule, CH$_4$, was used to investigate the steady state behavior of reactants in the reactor, and the use of a sweeping flow was found to be a suitable method for preventing wall deposition. The transient switching response of the gas manifold was also investigated. Under certain conditions (low velocities, unmatched flows) recirculation flows were apparent. Numerical calculations of the reactor gas dynamics gave reasonable agreement with experimental results when detailed thermal boundary conditions were included.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.114-117
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• 2007

In IRR(Integral Rocket-Ramjet), the booster is integrated into the ramjet combustor. Such combustors do not contain combustor liners or flame holders within the combustor due to the limited volume and flame stabilization depends on the recirculation zones formed by the sudden expansion region between the inlet duct and the combustor. A numerical study was conducted on the effect of flame holder which could be added to the inlet duct of IRR. Two different types of flame holder installations, flame holder without sudden expansion region and flame holder with small sudden expansion region, were compared and showed different flame shapes and pressure rise in the combustor.

• The KSFM Journal of Fluid Machinery
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• v.11 no.4
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• pp.38-44
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• 2008

This paper describes the performance and internal flow characteristics of two-stage high pressure ring blower. Chamber-type test rig is designed and manufactured for the performance test of the ring blower. Detailed flow characteristics inside the impeller and casing are analyzed by three-dimensional numerical simulation. Throughout numerical simulation, non-uniform inflow to the impeller inlet and reverse flow are observed near the inlet duct of the blower. This non-uniform inflow makes various recirculation flow inside the casing with the complicated shape of casing. Low velocity region is locally formed near the both sides of impeller outlet due to the non-uniform inflow to the impeller, thus deteriorates the performance of a ring blower.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.71-79
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• 2016

This paper introduces the design method of the centrifugal turbo fan and the process of developing the design program of it. The developed design program confirmed the applicability by experimental performance data. Here, we proposed new velocity coefficients and considered various losses such as impeller inlet loss, vane passage flow loss, casing pressure loss, recirculation loss power, and disk friction loss power. Especially, the inlet and outlet widths of the impeller were newly determined by reflecting the experimental results. As a result, this fan design program shows a good performance result regardless of the types of impeller and is expected to be a very useful design tool.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.722-725
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• 2004

An experimental investigation was conducted to investigate the effects of the equivalence ratio and air mass flux on the combustion efficiency in a solid fuel ramjet used fuel grains which were highly loaded with boron carbide. Combustion efficiency increased with increasing equivalence ratio (grain length), and decreasing air mass flux. Higher inlet air temperature produced higher combustion efficiencies, apparently the result of enhanced combustion of the larger boron particles those bum in a diffusion controlled regime. Short grains which considered primarily of the recirculation region produced larger particles and lower combustion efficiencies. The result of the normalized combustion efficiency increased with inlet air temperature, is coincident with the result of the Brayton cycle thermal and the total efficiency relating to the heat input.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.367-370
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• 2006

This paper deals with the modeling and simulation of the internal flowfield in a valveless airbreathing pulse detonation engine (PDE) currently under experimental development at the U.S. Naval Postgraduate School. The system involves no valves in the airflow path, and the isolation between the inlet and combustor is achieved through the gasdynamics in an isolator. The analysis accommodates the full conservation equations in axisymmetric coordinates, and takes into account variable properties for ethylene/oxygen/air system. Chemical reaction schemes with a single progress variable are implemented to minimize the computational burden. Detailed flow evolution during a full cycle is explored and propulsive performance is calculated. Effect of initiator mass injection rate is examined and results indicate that the mass injection rate should be carefully selected to avoid the formation of recirculation zones in the initial cold flowfield. Flow evolution results demonstrate a successful detonation transmission from the initiator to the combustor. However, strong pressure disturbance may propagate upstream to the inlet nozzle, suggesting the current configuration could be further refined to provide more efficient isolation between the inlet and combustor.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.5
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• pp.401-410
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• 2002

Concerns for energy conservation, environmental pollution, and the fact that organic wastes account for a major portion of our waste materials, have created the interest of biogas, which usually contains about 60 to 70 percent methane, 30 to 40 percent carbon dioxide, and other gases, including ammonia, hydrogen sulfide, mercaptans and other noxious gases. Cyclone combustors are used for homing a wide range of fuels such as low calorific value gas, waste water, sludge. coal, etc. The 3-dimensional swirling flow, combustion and emission in a tangential inlet cyclone incinerator under different inlet conditions are simulated using a standard k-s turbulence model and ESCRS (Extended Simple Chemically-Reacting System) model. The commercial code Phoenics Ver.3.4 was used for the present work. The main parameters considered in this work are inlet velocity and air to fuel ratio. The results showed that the change of operating conditions had an influence on the shape and size of recirculation zones, mixture fraction and axial velocity which are important factors for combustion efficiency and emission behavior. The application of this kind of computer program seams to be promising as a potential tool for the optimum design of a cyclone combustor with low emission.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.318-322
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• 2009

Supersonic ejectors are simple mechanical components, which generally perform mixing and/or recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for altitude testing of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement of ejector-diffuser performance by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow or recirculation pattern appears as one of the potential means of significantly improving low supersonic ejector-diffuser performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of ejector-diffuser system was improved for certain a range of system pressure ratios, where as there was no appreciable transition in the performance for lower pressure ratios and the orifice plate was detrimental to the ejector performance for higher pressure ratios. It is found that an appropriately sized orifice system should produce considerable improvement in the ejector-diffuser performance in the intended range of pressure ratios.