• Proceedings of the KSME Conference
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• 2000.11b
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• pp.491-496
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• 2000

The physics of the flow field surrounding an engine nacelle afterbody is very complex. A high pressure jet from the nozzle interacts with the external flow and causes upstream influence on the afterbody surface field. At certain conditions, the nozzle boundary layer can separate, either by shock wave interaction or by adverse pressure gradient effect, resulting in a severe drag penalty. Furthermore, a finite afterbody base implies a recirculating flow region. A flow modeling method has been developed to analyze the flow in the annular base(rear-facing surface) of a circular engine nacelle flying at subsonic speed but with a supersonic exhause jet. Real values of exhaust gas properties and temperature are included.

• Journal of ILASS-Korea
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• v.7 no.1
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• pp.1-6
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• 2002

This study has focused on using fuel injections as variables for measuring performance and reducing exhaust gas in turbo-charger diesel engine. In experiments, we changed nozzle hole diameter, diameter of an injection pipe, and injection timing as variable. The results show that torque. fuel consumption and smoke are reduced as nozzle hole diameter decreases, while NOx increases. When the diameter of injector is reduced, torque, fuel consumption and smoke are deteriorated, but NOx is decreased. In addition, when the time for injection is advanced. torque, fuel consumption and smoke are improved, but the density of NOx is increased.

• 발명특허
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• v.26 no.10 s.306
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• pp.76-83
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• 2001

본 발명은 승화성 고체 미립자 제트를 이용한 분사로 표면의 오염물을 제거하는 공정이다. 이는 극저온에서 고화된 입자가 표면에 고속 충돌 후 오염물을 제거하고 자신은 승화되어 잔사를 남기지 않는 청정 세척 공정을 말하는데 반도체 장비, 정밀 제품, 인쇄회로 기판 등의 다양한 표면의 각종 오염막 제거에 널리 사용될 수 있다. 본 장치의 특징은 세정 매체인 $CO_2$와 Carrier gas인 $N_2$를 사용하였고 현재 특허에 출원되어 있는 단순한 액체$CO_2$를 이용한 세정범위를 넘어 다양한 세정매체 즉, 복합인자($CO_2$ + ice, Ar + ice)를 이용하여 세정효율의 다변화를 이루었고 자체 개발한 냉동기를 이용하여 고화율이 액체 $CO_2$보다 상대적으로 낮은 기체 $CO_2$의 고화율을 증대 시킴으로써, 세정매체의 소모시간이 현격히 감소되어 원가절감 효과를 증대 시켰다. 세정대상물을 효과적으로 제거하기 위해 주 세정 매체인 $CO_2$의 수농도를 조절할 수 있는 Multi-Nozzle의 개발과 이로 인하여 세정력의 강도를 조절하도록 하였다. 세정 후 발생되는 오염입자를 효과적으로 제거하도록 국부 Exhaust를 Nozzle전단에 달아 재 오염의 방지효과를 극대화 시켰다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.359-364
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• 2004

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions from the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO$_x$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO$_x$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO$_x$ emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.46-55
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• 2005

For the sea-level performance test of rocket motor designed to operate in the upper atmosphere, ejectors with no induced secondary flow are generally used, which serves dual purposes of evacuating the test cell and performing as a supersonic exhaust diffuser (SED). The main concern of this research is to simulate starting transients in order to visualize evolution of internal shock structures in SED with different initial cell (vacuum chamber) pressures. RANS code with low Reynolds $k-\varepsilon$ turbulence model was employed for these computations. Numerical results were compared with the pressure measurements previously performed [Proceedings of 2004 Annual Conference, KIMST], and showed good agreements with pressure-time history of measured data. In the case of low vacuum chamber pressure, abrupt impingement of the under-expanded supersonic jet from the nozzle onto the diffuser wall was observed, whereas initial impingement point was located downstream and moved slowly upstream in the case of non-vacuum chamber pressure. In spite of initially dissimilar evolution of shock structures, iso-mach contour revealed that the steady shock structures had little difference except the location of flow separation and normal shock.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2642-2647
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• 2008

Starting characteristics of the axi-symmetric supersonic exhaust diffuser(SED) with a second throat are numerically investigated. Main purpose of this study is to predict theoretical starting pressure of STED using 1-D normal shock theory and to present the range of optimum starting pressure through parametric study with essential design parameters of STED influencing on starting performance. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. Minimum(optimum) starting pressure difference of $20{\sim}25%$ between 1-D theory and experimental evidences validated from previous results[5] is also applied to predict those in this system. The analysis results indicate that dominant parameters for diffuser starting in this system is diffuser expansion ratio($A_d/A_t$), which has optimum value 120 and second throat area ratio($A_d/A_{st}$), which has optimum range $3.3{\sim}3.5$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.934-939
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• 2007

Thrust vector control(TVC) is the method which generates the side force and moment by controlling the exhausting gas directly from the supersonic nozzle to change the trajectory of a missile quickly. In this paper, performance study on the tapered ramp tabs asymmetrically installed in the supersonic nozzle exhaust for the thurst vector control has been carried out using the supersonic cold flow system. To study the shock wave structure and location of the oblique shock wave produced by the ramp tab, the flow field visualization using the schlieren system is conducted. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.443-452
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• 2005

The purpose of this study is experimentally to analyze the effects of intake port swirl, injection system and turbocharger on the engine performance and the emission characteristics in a V8 type turbocharger intercooler D.I. diesel engine of the displacement 16.7L, and to suggest the improvement of engine performance. Generally to enhance engine power, TCI diesel engine is put to practically use turbocharged intercooler in order to increase volume efficiency which is cooled boost air. As results of considering the factors of the intake port of swirl ratio 2.25, compression ratio 17.5. re-entrant $8.5^{\circ}$ combustion bowl, nozzle hole diameter ${\phi}0.33{\ast}3+{\phi}0.35{\ast}2$. nozzle protrusion 3.18mm, injection timing BTDC $12^{\circ}CA$ and turbocharger(compressor 0.6A/R+46Trim. turbine 1.0 A/R+57Trim) is the best in the full load in the engine performance and the exhaust characteristics of NOx concentration. Therefore. their factors are appropriated as intake system, injection and turbocharger system.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.63-69
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• 2014

The oxidizer-rich preburner's combustion tests were fulfilled in the development process of staged combustion cycle rocket engines. The exhaust plume from an oxidizer-rich preburner is relatively transparent because combustion takes place in oxidizer rich state. During hot fire tests a still and infrared images were captured to visualize the plume structure, temperature distribution and so on. In addition, the exhaust plume was numerically investigated to figure out the detailed characteristics. The combustion was not considered for the numerical modeling, but the mixing of exhaust plume with circumstantial air was modeled by species transport model with several turbulence models. The inner structure of plume was configured out by the comparison of numerical results with experimental results, and the validity of applied numerical models was verified.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.802-806
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• 2004

For the protection of the local air quality and the global atmosphere, the emissions of trace species including nitric oxides (NO and NO$_2$) from gas turbines are regulated by local governments and by the International Civil Aviation Organization. In-situ measurements of such species are needed not only for the development of advanced low-emission combustion concepts but also for providing emissions data required for the sound assessment of the effects of the emissions on environment. We have been developing a laser absorption system that has a capability of simultaneous determination of NO and NO$_2$concentrations in the exhaust jets from aero gas turbines. A diode laser operating near 1.8 micrometer is used for the detection of NO while a separated visible tunable diode laser operating near 676 nanometers is used for NO$_2$. The sensitivities at elevated temperature conditions were determined for simulated gas mixtures heated up to 500K in a heated cell of a straight 0.5 m optical path. Sensitivity limits estimated as were 30 ppmv-m and 3.7 ppmv-m for NO and NO$_2$, respectively, at a typical exhaust gas temperature of 800K. Experiments using the simulated exhaust flows have proven that $CO_2$ and $H_2O$ vapor - both major combustion products - do not show any interference in the NO or NO$_2$ measurements. The measurement system has been applied to the NO/NO$_2$ measurements in NO and NO$_2$ doped real combustion gas jets issuing from a rectangular nozzle having 0.4 m optical path. The lower detection limits of the system were considerably decreased by using a multipass optical cell. A pair of off-axis parabola mirrors successfully suppressed the beam steering in the combustion gas jets by centralizing the fluctuating beam in sensor area of the detectors.