• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.13-15
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• 2014

최근 경제적인 연비와 효율적인 가동성, 배기가스 감소의 이유로 초임계압 보일러가 각광받고 있다. 하지만 보일러 연소로는 용접된 튜브로 구성되어 있기 때문에 연소 시 내부압력에 의해 발생되는 진동에 취약하여 이에 대한 진동안정성 평가가 필요하다. 본 논문에서는 CFD 기법을 기반으로 수행한 변동압력 해석과 단순화한 모델을 이용한 진동해석을 통하여 보일러 운전 시의 진동안정성 평가를 수행하였다. 변동압력해석은 정상상태 CFD 해석을 수행하고, 이를 이용한 음향모드 해석과 비정상상태 CFD 해석에서 변동압력을 추출하고, 음향모드 해석결과와 주파수 성분을 비교하여 검증하였으며 이를 진동해석 모델에 기진력으로 적용하여 보일러 연소로의 진동해석을 수행하였다. 진동해석 모델은 동특성을 고려한 등가물성치를 이용하여 연소로의 복잡한 구조를 단순화하였으며 buckstay 등의 방진구조를 구현하여 보일러의 진동안정성을 평가하는 기법을 정립하였다. 해석결과, 보일러 운전조건에서 비정상상태 CFD 해석을 통해 구한 변동압력과 진동해석을 통해 얻은 가속도 응답은 안정적 수준인 것으로 확인하였다. 이는 향후 유사한 보일러 안정성 평가에 적용이 가능하고, buckstay 등 보일러의 방진 구조 설계 및 평가에도 적용할 수 있음을 확인할 수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.261-264
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• 2008

This study experimentally examines combustion characteristics of a hybrid rocket in which solid paraffin is used as a fuel, while oxidizer is pure oxygen. Especially, the experiment investigates the effects of chamber pressure and configuration of fuel grain. The pressure inside the combustion chamber is varied by changing a flow rate of oxidizer. The regression rate is observed to increase as the chamber pressure does. There also exists the effects of shape of fuel grain on thrust. Characteristic of paraffin hybrid rocket changes with shape of fuel grain. When there is a room near the injector, thrust increases. On the other hand, the room near the nozzle does not contribute to thrust increasement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1995.11a
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• pp.171-177
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• 1995

추진기관 연소관 제작시 발생하는 결함등에는 주로 표면결함의 형태의 것이 많은데 연소관 설계시 이러한 결함들의 영향을 고려하는 것이 구조물의 안정성에 있어 중요한 요소가 된다. 따라서 본 논문에서는 연소관에 발생할수 있는 결함들에 대한 파단하중 및 파단압력에 대한 탄성 및 탄소성해석을 통하여 파괴 매개변수인 J적분을 유한요소 프로그램인 ABAQUS를 이용하여 3차원 비선형해석을 수행하여 5가지의 균열모델을 사용하여 평판, 양단개방 압력용기(open tube) 및 양단막힘 압력용기 (closed tube)의 파단하중하에서의 J적분의 영향을 분석하였다. 평판 결함시편의 J적분으로부터 압력용기의 손상허용설계를 할 수 있는 방안을 조사 하였으며 추진기관 연소관에 적용하여 발생가능한 크기의 결함에 대한 안정성을 조사한결과 충분한 안정성을 확보하고 있음을 알수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.243-246
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• 2008

The combustion characteristic of solid fuel with chamber pressure were experimentally studied in hybrid combustion. This paper was experimental confirmed whether solid fuel affected not only oxidizer mass flux but also chamber pressure. Poly-Ethylene(PE) was used as fuel, GOX was used as oxidizer. Chamber pressure was controled by nozzle throat diameter 6mm and 9mm. In low oxidizer mass flux, solid fuel regression rate was affected not only oxidizer mass flux but also chamber pressure. As well, the regression rate increase as chamber pressure increase with same oxidizer mass flux.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.29-29
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• 1999

점화천이(Ignition transient)는 일반적으로 점화 신호를 주는 순간부터 로켓모타가 평형상태(equilibrium) 혹은 설계 작동조건에 도달했을 때까지의 시간 구간으로 정의되며, 이 시간 동안에 높은 연소실 압력 증가율에 의한 동연소효과(dynamic burning effect)와 연소가스의 높은 cross-flow 속도에 의한 침식연소효과(erosive burning effect)에 의해 추진제의 연소증가 현상을 일으킨다. 이런 두가지의 증가된 연소효과와 더불어 과대하게 설계된 점화기로부터 유입되는 질량유량에 의해 연소실을 채우는 시간(Chamber filling) 중에 압력 과잉(pressure overshoot)이 나타난다 그러나 동연소효과 및 침식연소효과의 경우 추진제의 종류와 로켓모타의 형상 등에 의해서 복합적으로 나타나는 현상이기 때문에 모든 로켓모타에 대해서 공통으로 적용할 수식이나 방정식이 존재하지 않는다.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.3
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• pp.50-57
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• 2009

A gas mechanical pulsator is developed for the study of combustion instabilities in various combustors such as LRE combustor. First, it shows that the mass flow rates and the perturbation frequencies can be successively controlled by the inlet pressure and the rotating speed of a rotating disk with many holes. Second, the device is used as an acoustic amplification source as a substitute for the speaker in the previous acoustic tests and its results show almost the same resonant frequency and damping characteristics compared with the previous results. In conclusion, the result shows that it can be used as a substitute for a speaker in the studies of LRE combustion instabilities, which has a flow and no limitation of amplification, and a device for making a perturbation source in gas flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.520-526
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• 2012

The appearance of the negative differential pressure(NDP), in which the shot base pressure is higher than the breech pressure, indicates that a potential damage on the gun system is increased. In order to safeguard the gun system, the igniter must be designed to minimize the NDP during the firing process. From this reason, the effect of igniter's burning rate on the NDP of the interior ballistics has been investigated through the numerical simulations. The NDP has been increased with increment of the coefficient in the burning rate of the igniter. A sudden change of the chamber pressure has been shown in case of using a singular coefficient.

• Journal of the Korean Institute of Gas
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• v.16 no.1
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• pp.8-14
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• 2012

Hydrogen is considered to be the most important future energy carrier in many applications reducing significantly greenhouse gas emissions, but the explosion safety issues associated with hydrogen applications need to be investigated and fully understood to be applicable as the carrier. The risk associated with a explosion depends on an understanding of the impacts of the explosion, particularly the pressure-time history during the explosion. This work provides the effects of explosion parameters, such as specific heat ratio of burned and unburned gas, equilibrium maximum explosion pressure, and burning velocity, on the pressure-time history with flame growth model. The pressure-time history is dominantly depending on the burning velocity and equilibrium maximum explosion pressure of hydrogen-air mixture. The pressure rise rate increase with the burning velocity and equilibrium maximum explosion pressure. The specific heat ratio of unburned gas has more effect on the final explosion pressure increase rate than initial explosion pressure increase rate. However, the specific heat ratio of burned gas has more influence on initial explosion pressure increase rate. The flame speeds are obtained by fitting the experimental data sets. The flame speeds for hydrogen in air based on our experimental data is very low, making a transition from deflagration to detonation in a confined space unlikely under these conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.69-75
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• 2003

The ideal thrust function is used to determine the local thrust of supersonic combustor. Method of thrust determination from measured pressures are applied to the Mach 2.5 model supersonic combustor. In this application, measured pressures from the experiments in the University of Michigan are used to determine the local thrust of supersonic combustor. Marginal results of local thrust are obtained and discussed. Combustion and wedge affect thrust distributions in the upstream region significantly. The thrust determination from pressure measurements can be a simple, feasible and applicable method, especially when thrust stand is not available.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.12-18
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• 2021

This study aimed at preparing the solid propellants featuring high pressure exponent available for throttleable rocket system development. The combustion properties of solid propellant based on PCP as a prepolymer were investigated with the different nitramine oxidizer, HMX and HNIW. As a main oxidizer, HNIW could deliver higher burning rate, specific impulse and flame temperature than HMX. In addition, the introduction of AP as a co-oxidizer in PCP/Nitramine propellants could enhance burning rate, specific impulse and flame temperature, showing the lower pressure exponent with increasing the content of fine-sized AP, total solids and plasticizer. Moreover, we examined the temperature sensitivity on burning rate of propellants between 150 psia and 2,500 psia.