• Proceedings of the KSME Conference
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• 2001.06d
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• pp.49-53
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• 2001

A conventional flame type gas combustion major portion of heat is transferred to the body by convection due to small radiant ability of the gas flame. Increasing the radiation component of heat flux in the combustion zone allows to augment the efficiency of gas utilization. Such effect can be reached by using radiative gas burner applied to metal mesh combustion. Basically the gas radiant burner consists of metallic mesh of high heat resisting steels. In terms of this regards, we have made the burner consisted of metal mesh and measured the radiative flame stability of natural gas/air mixture on the metal mesh burner. The pressure loss through the metal mesh is defined by pressure-velocity slope. The more increased the pressure-velocity slope of the metal mesh is, the wider the stable zone of radiave flame on the metal mesh burner is. And the augmentation of mixture flowrate through the metal mesh make narrow the permissible range of equivalence ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.536-542
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• 2017

A great deal of difficulty is encountered in the thermo-mechanical analyses of nozzle assembly for solid propellant rocket motors. The main issue in this paper is the modeling of the boundary conditions and the connections between the various components-gaps, relative movements of the components, contacts, friction, etc. This paper evaluated the complex phenomena of nozzle assembly during burning time with co-simulation which include fluid, thermal surface reaction/ablation and structural analysis. The validity of this approach was verified by comparison of analysis results with measured strains.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.36-43
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• 2018

A great deal of difficulty is encountered in the thermo-mechanical analyses of nozzle assemblies for solid propellant rocket motors. The main issue in this paper is the modeling of the boundary conditions and the connections between the various components-gaps, relative movements of the components, contacts, friction, etc. This paper evaluates the complex phenomena of nozzle assemblies during burning time with co-simulations that include fluid, thermal surface reaction/ablation, and structural analysis. The validity of this approach is verified via comparison of analysis results with measured strains.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.

• Elastomers and Composites
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• v.49 no.4
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• pp.305-312
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• 2014

Most of military supersonic aircraft use an afterburner. It plays an important role in performing unusual duties for supersonic flight, takeoff, and combat situations. Recently, repetitive fuel leakage from the inner piston packing rubber of afterburner fuel pump in an aircraft J85-GE-21 turbojet engine has happened. These failures have only happened in one manufacturer's parts of two manufacturers. Thus, the cause of these failures was investigated through the comparative analysis for both the failed and the unfailed with two different manufacturers using various analysis methods. The failure analysis was performed using analysis methods such as swelling or swelling ratio, total sulfur content, polymer identification, loading and surface area of carbon black, and hardness. Consequently, the main cause of this failure was identified to be insufficient loading of carbon black as a reinforcing agent, together with small surface area of carbon black and somewhat low sulfur content.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1633-1639
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• 1993

In spark ignition engine, EGR of lean mixture operation has advantage in emission, but disadvantages in power output and combustion flame propagation. Fast burn system is known to be a useful method to solve these disadvantages. This paper presents the characteristics of in-cylinder flow for different combustion chamber geometries, and the correlation between the in-cylinder flow and the combustion flame speed using an ion current method.

• Journal of the KSME
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• v.25 no.3
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• pp.236-241
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• 1985

본 고에서는 일반적으로 노즐 부위 열해석에서 무시되는 복사열전달율과 점성소산효과를 수치적 모델을 통하여 그 필요성 여부를 조사한 것이며 다음과 같은 결론을 얻었다. (1)연소실 및 수 렴부위에서는 복사열전달율이 대류열전달율과 같은 차수의 크기로 나타나고 있어서 고 복사율을 갖는 연소가스에서는 특히 중요하다. 특히 최근에 많이 사용되는 연료에는 연소가스에 산화알 루미늄 성분이 증가하는 추세이므로 노즐부위 열해석에는 복사열전달이 차지하는 비중이 커질 것이다. (2)노즐의 확산부위에서는 고속으로 인하여 가스자체의 점성소산이 일어나 특성치 보 정계수 값이 감소한다. 따라서 Bartz의 예측치 보다는 열전달계수의 값이 적어지고 있다. (3) 따라서 노즐수렴부위에서는 일반적으로 Bartz의 예상치보다 높고 확산부에서는 낮은 결과를 얻 었던 실험결과와를 비교할 때 고온고속 노즐에서의 열전달해석은 복사 열전달과 점성열 소산을 고려함으로써 정확하게 될 수 있다. (4)이상 고려된 실험 데이터와 수치모델의 고찰은 노즐내의 침식이 없는 경우이나 실제의 경우 노즐벽 표면에서 화학적 반응이 일어난다. 그러나 이때 발 생될 수 있는 순수한 발한효과는 미미하며 단지 전체적인 단면의 열 해석시 상기에서 예측된 열전달율을 근간으로 화학반응열 및 온도분포를 계산하여야 할 것이다.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.1-10
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• 2005

The combustion reactivity of char depending on the pyrolysis pressure was investigated with Pressurized Thermogravimetric Analyser. The amounts of volatiles released at pyrolysis pressure of 1, 8 and 15 atm were, first, measured with Alaska, Adaro and Denisovsky coals. Reactivities of chars produced at var-ious pyrolysis pressure were evaluated at atmospheric pressure and 500℃, and analysed in terms of char crystal structure, surface area, pore characteristics and chemical composition of char. Finally, the combustion reactivities of three chars were examined at pressure of 1 atm, 8 atm and 15 atm. From this study, it was recognized that the amount of volatiles released decreases with increase in pyrolysis pressure, and reaction rate of char produced at higher pyrolysis pressure was lower than that at lower pyrolysis pressure. It might be resulted from the difference in char surface area and pore characteristics rather than char crystal structure and chemical characteristics. At 15 atm, kinetic parameters of Alaska char were obtained with the grain model, and these were 56.8 KJ/mole for activation energy and 222.34 (1/min) for frequency factor.

• Fire Science and Engineering
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• v.34 no.4
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• pp.101-106
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• 2020

This study analyzed flame growth characteristics and carbonization patterns when floor materials were burned vertically using a needle flame produced for this study. It was found that PVC flooring was fire retardant and the area under direct flame contracted inward. Vertical combustion causes solidification in the form of a lump at the bottom and also generates soot in a pattern that progresses upwards. This study found that laminated flooring exhibited no fire retarding characteristics and that the laminated layer of its upper surface was destroyed by fire, causing irregular delamination. The carbonization ranges at the left and right sides were determined to be symmetrical. A vertical combustion test of a sample carpet showed that it exhibited no fire-retarding characteristics. It was observed that if heat accumulated in the carpet, the flame formed an ascending air current, and that when flammable materials were present around the flame, they further accelerated the diffusion of the flame. The carbonization pattern at the carpet surface exposed to direct flame revealed that the carpet surface had melted and had flown downwards and that many tiny holes formed on it.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.61-65
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• 2005

In HTPB/AP propellants, zirconium(Zr) addition to formulation was shown to be less specific impulse than aluminum(Al) by the theoretical calculation because of the lower flame temperature and higher molecular weight of Zr oxide. It was found that the burning rate was faster with the finer size of Zr and the more content of $2{\mu}m$ Zr the faster burning rate is in HTPB/AP/Zr propellants caused by the more conduction energy transfer from Zr flame to the burning surface. Also the burning rate of HTPB/AP/Zr propellant could be reduced by addition of 150nm Al, depending on AP size distribution in formulation with Butacene and $1{\mu}m$ AP.