• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.778-787
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• 1999

In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.632-640
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• 1996

The ignition and combustion characteristics of CWS droplets were investigated in the postflame region generated by a flat burner. The effect of radiation by screen and heating eleements ws taken into account. Also the theoretical claculations considering the temporal temeprature variation have been performed and compared with experimental results. The ignition delays were reduced by the radiation of the screen or heating elements. Therfore the radiation was considered to play some role in predicting the ignition delay.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.168-171
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• 2007

A technical review of current slurry and gelled propellants is presented. In advanced countries, it is confirmed that these propellants have high specific impulse, density, excellent handling, safety characteristics and thrust controllability through research since 1950s. Substantial researches have been pursued to characterize the rheological properties, spray/combustion phenomena and propulsion system design for the gel propellant characteristics. Slurry and gelled propellants are developing actively to applicate both military and space propulsion fields such as tactical missile, air-breathing ramjet, pulse detonation engine, and combined cycle engine of future propulsion mode.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.42-47
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• 2004

Air-fuel mixing and flame-holding are two important factors that have to be considered in the design of an injection system. Different injection strategies have been proposed with particular concern for rapid air-fuel mixing and flame-holding. Two representative injection techniques can be applied in a supersonic combustor. One of the simplest approaches is a transverse(normal) injection. The cavity flame holder, an integrated fuel injection/flame-holding approach, has been proposed as a new concept for flame holding and air-fuel mixing in a supersonic combustor. This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of a model scramjet engine combustor, where hydrogen is injected into a supersonic cross flow and a cavity. The combustion phenomena in a model scramjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, were observed around the separation region of the transverse injector upstream and the inside cavity. The results show that this flow separation generates recirculation regions which increase air-fuel mixing. Self-ignition occurs in the separation-freestream and cavity-fteestream interfaces.

• Transactions on Electrical and Electronic Materials
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• v.3 no.3
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• pp.34-38
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• 2002

In this paper, efficiency estimation of toxicity fee fire resistance cable experiments was measured smoke density of toxicity free fire resistance polyolefin insulation material and electric field dependence of tree shape in low density polyethylene (LDPE). One of the most serious causes of failure in high-voltage cables, can be an electrical discharge across an internal gab or void in the insulating material. Treeing due to partial discharge is one of the main causes of breakdown in the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation and research of the fire resistance character has become important. First, we have studied on electric field dependence of tree shape in LDPE about treeing phenomena occurring on the high electrical field. Second, the measurement method is the attenuation quantity of irradiation by smoke accumulating with in a closed chamber due to non-flaming heat decomposition and flaming combustion. A main cause of fire-growth and generating toxic gas when, it bums, should be dealt with great care in life. safety design. The fire gases were occurred carbon monoxide and decomposition than in polyolefin due to incomplete combustion of PVC, which has high content of carbon in chemical compound.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.97-100
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• 2011

It is critical to set up the starting sequence of liquid rocket engines because not carefully arranged process can lead the engine damages. Thus, many efforts were made to prevent the hard start at the ignition. Hypergolic fuels are frequently used to ignite LRE and TEAL, one of the hypergolic fuel is also used for kerosene-LOx LRE ignition. However, since we are still lack of experiences igniting oxygen rich preburners of the staged combustion cycle engines, it would be helpful to estimate the TEAL ignition phenomena before the actual tests.

• Advances in aircraft and spacecraft science
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• v.6 no.4
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• pp.333-348
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• 2019

Low fuel regression rate is the main drawback of hybrid rocket which should be overcome. One of the improvement techniques to this problem is usage of a solid fuel grain with a complicated geometry port, which has been promoted owing to the recent development of additive manufacturing technologies. In the design of a hybrid rocket fuel grain with a complicated geometry port, the understanding of fuel regression behavior is very important. Numerical investigations of fuel regression behavior requires a capturing method of solid fuel surface, i.e. gas-solid interface. In this study, level set method is employed as such a method and the preliminary numerical tool for capturing a hybrid rocket solid fuel surface is developed. At first, to test the adequacy of the numerical modeling, the simulation results for circular port are compared to the experimental results in open literature. The regression rates and oxidizer to fuel ratios show good agreements between the simulations and the experiments, after passing enough time. However, during the early period of combustion, there are the discrepancies between the simulations and the experiments, owing to transient phenomena. Second, the simulations of complicated geometry ports are demonstrated. In this preliminary step, a star shape is employed as complicated geometry of port. The slot number effect in star port is investigated. The regression rate decreases with increasing the slot number, except for the star port with many slots (8 slots) in the latter half of combustion. The oxidizer to fuel ratio increases with increasing the slot number.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.203-209
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• 1999

LaAlO3d single phase used as the butter layer on Si wafer for YBa2Cu3O7-$\delta$ superconductor application were prepared by solid state reaction method and by self-sustaining combustion process. The microstructure and crystallity of synthesiszed LaAlO3 powder studied using scanning electron microscope (SEM) and X-ray diffractometer(XRD), specific surface area and sintering characteristics fo powder were investigated by Brunauer-Emmett-Teller (BET) method and dilatometer respectively. In solid state reaction method, it is difficult to obtain LaAlO3 single phase up to 150$0^{\circ}C$ period. However, in self-sustaining combustion process, it is to easy to do it only $650^{\circ}C$. Based on the results of analysis of dilatometer it is easier to obtain high sintering density (98.87%) in self-sustaining combustion process than in the solid state reaction method. This reason is that the average particle size prepared by self-sustaining combustion process is nano crystal size and has high specific surface are value(56.54 $m^2$/g) compared with that by solid state reaction method. Also, LaAlO3 layer on the Si wafer has been achieved by screen printing and sintering method. Even though the sintering temperature is 130$0^{\circ}C$, the phenomena of silicon out diffusion in LaAlO3/Si interphase are not observed.

• The Journal of the Acoustical Society of Korea
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• v.18 no.7
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• pp.56-66
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• 1999

Thermoacoustic oscillation is a significant problem in cylindrical-type combustors such as common internal combustion engines, industrial furnaces, gas turbine, etc. This kind of low frequency oscillation can lead to serious consequences such as destruction of the combustor and production of strong noise. The accurate numerical simulation of thermoacoustic phenomena is a complex and challenging problem, especially when considering the chemical reaction of mixtures. As with other simulations of aerodynamics and aeroacoustics, the direct computation of thermoacoustic phenomena requires that Navier-Stokes equations be solved using accurate numerical differentiation and time-marching schemes, with non-reflecting boundary conditions. The numerical approach used here aims at qualitative analysis and efficient prediction of those problems, not at the development of an accurate scheme. The numerical prediction developed in this work is shown to be reasonably matched with experimental result.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.36-36
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• 2000

액체로켓엔진에 사용되는 2000psi이상의 고압 연소실(Combustion Chamber)의 냉각은 내피(Inner Shell)에 기계 가공된 냉각통로(Cooling Channel)로 냉각제를 흘려보내는 재생냉각방식이 널리 사용되며 기계 가공된 냉각 통로는 외피(Outer Shell)에 의해서 지지 밀봉된다. 일반적으로 내피 재료는 순수한 구리보다 강도가 우수하고 열전도도는 유사한 구리합금을 사용하고, 외피는 강도가 우수한 스테인레스 강을 사용하여 브레이징 접합된 구조를 형성한다. 브레이징 공정은 조립품을 약 $450^{\cire}C$ 이상의 액상선을 갖는 삽입금속(Filler Metal)을 사용하여 적당한 온도($450^{\cire}C$ ~ 모재의 고상선)에서 가열하여 접합시키는 방법으로, 용융 금속의 젖음 현상(Wetting Phenomena), 접합 틈새(Joint Clearance)로의 용융 삽입금속의 유입(Capillary Phenomena)과 접합 계면의 반응을 통해서 접합이 이루어진다. 이는 일반적인 접합 공정과 비교하여 모재의 변형이 적고, 이종 금속 간의 접합이 용이하며, 복잡한 부품을 정밀하게 접합할 수 있는 장점이 있으나, 접합될 제품의 표면 상태 및 분위기(Atmosphere), 접합될 부품간의 조립 틈새, 가열 싸이클(Heating Cycle) 등에 대한 공정 확립 및 관리가 매우 중요하다. 재생냉각 구조를 갖는 연소실은 우선 접합면의 형상이 매우 복잡하여 균일한 접합 틈새를 유지하면서 접합시키기가 매우 어려우며, 고온, 고압의 환경에서 작동하므로 일부 접합면이 접합되지 않을 경우 내피의 변형 및 파괴가 발생하고, 브레이징 시 용융된 삽입금속이 냉각통로 내로 유입될 경우 연소 시 이부근에서 재료의 용융이 발생될 수 있다. 따라서, 이러한 현상을 방지하기 위해서는 진공 분위기 하에서 적절한 접합 틈새를 유지할 수 있는 공정 및 장비의 개발이 필요하다.