• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.27-30
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• 2007

We have been setting up experiments on propagation of shock waves generated by the pulsed laser ablation. One side of a thin metal foil is subjected to laser ablation as a shock wave is generated from a localized spot of high intensity energy source. The resulting reactive shock wave, which penetrates through the foil is reflected by an acoustic impedance which causes the metal foil to high-strain rate deform. This short time physics is captured on an ICCD camera. The focus of our research is generating reactive shock wave and high strain rate deforming of thin metal foil for accelerating micro-particles to a very high speed on the orders of several thousand meter per second. Somce innovative applications of this device will be discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.35-35
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• 1998

고체 로켓 추진기관의 노즐을 개발하기 위해서는 주어진 체계 제한 조건내에서 기본적인 가스의 동력학, 내탄도에 의한 형상 설계, 재료 개발 및 적용 기술, 열전달 계산에 의한 열설계 및 해석 등이 종합적으로 적용되며 수많은 반복과정을 거쳐야 한다. 특히 최근에는 알루미늄 함유량을 증가시켜 연소가스의 온도가 300$0^{\circ}C$ 이상이 되는 고성능 추진제가 일반적으로 적용되고 있으므로 고온에 의한 열적문제가 심각하게 대두되고 있으며 이에 견디는 신뢰도가 높은 노즐 설계개발이 요구되고 있다. 노즐목을 노즐내에서 열부하가 가장 심한 곳으로 노즐목 확대에 의한 추력 손실을 최소화하기 위해 내삭마성이 강한 재료를 선정하여야 하며, 그래파이트는 이러한 조건을 만족시키는 소재의 하나로 많이 적용되고 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.943-951
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• 1992

The objectives of this study are to analyse the thermal response behavior occurring in the charring ablative material more realistically by considering ablation and char phenomena occurring in several material layers, and to increase the reliability of thermal analysis by being able to get stable solutions through using the finite analytic method. A program has been developed to predict the temperature distribution, ablation thickness, char thickness, ablation velocity and char velocity by solving non-linear one-dimensional heat conduction equation. Results of calculation were compared with results of published papers. From this compariosn this program was proved to be a very good tool for thermal design and analysis of charring ablative materials used in the rocket propulsion system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.425-429
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• 2011

The development of metal plasma generated by high laser irradiance and its effect on the surrounding air using shadowgraph images after laser pulse termination are studied; hence the formation of laser supported detonation and combustion processes has been investigated. The core of the paper is in detecting chemical reaction using X-Ray Diffraction (XRD) between ablated aluminum plasma and oxygen from air by inducing high power laser pulse (>1000 mJ/pulse) and conduct a quantitative comparison of chemically reactive laser initiated waves with the classical detonation of exploding aluminum (dust) cloud in air. This study may suggest a new approach of initiating detonation from metal sample in its bulk form without the need of mixing nano-particles with oxygen for initiation.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.227-233
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• 2007

Carbon/carbon (C/C) composites as unique materials possess exceptional thermal resistance with light weight, high stiffness, and strength even at high temperature. However, one serious obstacle for application of the C/C composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating has been employed to protect the composites from oxidation. This study explored combustion characteristics of 4-directional (4D) carbon/carbon composites using liquid fuel rocket engine to investigate ablative motion of the materials. C/C composites were made of coal tar pitch as a matrix precursor, and heat-treated at $2300^{\circ}C$. Throughout repeated densification process, the density of the material reached $1.903g/cm^3$. After machining 4D C/C composites, the nozzle surface was coated by a SiC layer by pack-cementation method to improve oxidation resistance. Erosion characteristics of SiC-coated C/C composites were measured as function of the ratio of oxygen to fuel. The morphological change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.119-125
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• 2017

Ablative material in a rocket nozzle is exposed to high temperature combustion gas, thus undergoes complicated thermal/chemical change in terms of chemical destruction of surface and thermal decomposition of inner material. Therefore, method for conjugate analysis of thermal response inside carbon/phenolic material including rocket nozzle flow, surface chemical reaction and thermal decomposition is developed in this research. CFD is used to simulate flow field inside nozzle and conduction in the ablative material. A change in material density and a heat absorption caused by the thermal decomposition is considered in solid energy equation. And algebraic equation under boundary layer assumption is used to deduce reaction rate on the surface and resulting destruction of the surface. In order to test the developed method, small rocket nozzle is solved numerically. Although the ablation of nozzle throat is deduced to be higher than the experiment, shape change and temperature distribution inside material is well predicted. Error in temperature with experimental results in rapid heating region is found to be within 100 K.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.6
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• pp.523-530
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• 2017

Laser-Induced Breakdown Spectroscopy (LIBS) which a plasma is irradiated at a specific wavelength depending on the material when a high-energy laser is irradiated, and a Raman spectroscopy which measures rotation and vibration in molecules as light-scattering phenomenon occurs, are attracting attention as a space exploration technology because of the advantages of high accuracy and real-time analysis, and the ability to perform long-range detection. In this study, the tendency of the laser spectrum according to the change of the soil component was analyzed by laser spectroscopy and the two - dimensional chemical distribution was conducted based on the trend of laser spectrum. We have also established the environment of Mars (4-7 torr) and lunar atmosphere (<1 torr) in experimental setup, to prove that it is possible to measure by difference of soil chemical composition using LIBS and Raman spectroscopy even in artificial space environment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.197-204
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• 2012

We explore the evolution of metal plasma generated by high laser irradiances and its effect on the surrounding air by using shadowgraph images after laser pulse termination and X-ray diffraction (XRD) of aluminum plasma ablated by a high-power laser pulse (>1000 mJ/pulse) and oxygen from air. Hence, the formation of laser-supported detonation and combustion processes has been investigated. The essence of this paper is in observing the initiation of chemical reaction between the ablated aluminum plasma and oxygen from air by the high-power laser pulse (>1000 mJ/pulse) and in conducting a quantitative comparison of the chemically reactive laser-initiated waves with the classical detonation of an exploding aluminum (dust) cloud in air. The findings in this work may lead to a new method of initiating detonation from a metal sample in its bulk form without any need to mix nanoparticles with oxygen for initiation.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.48-56
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• 2011

A Possibility of combustion instability on longitudinal mode has a high level at large scale of L/D. Solid propellant has a metal particle and a grain of control to pressure oscillation. Solid rocket motor in slotted-tube grain controls pressure oscillation of longitudinal mode. Slotted-tube grain restrains longitudinal 1st pressure oscillation. But cavity volume of aft. insulation ablation amplifies 2nd pressure o scillation by vortext shedding. A study has suppressed combustion instability and vortex shedding by modified 4 slotted tube solid rocket motor design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.699-705
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• 2011

High-maneuver missile is a projectile which demands a strong momentum at short time. To produce a necessary thrust for the flight, the gas of high temperature and pressure is generated through explosive combustion of solid propellant, and a great thrust can be obtained by expanding this high temperature and pressure gas. Although the operating time of a rocket motor is less than a few seconds, a failure of part or ablation near the throat of nozzle may take place during the expansion of high temperature and pressure gas for great thrust. In other words, for the precise control of a missile an exact stress analysis considering both, the thermal stress caused by the heat transfer between combustion gas and wall, and the mechanical stress caused by the pressure change in the flow, should be considered first. In this connection, this study investigated the safety, as a point of view of stress and melting point of the material, of the pre-designed thrust generating structure which is subjected to high temperature and pressure as a function of motor operating time.