• 한국연소학회:학술대회논문집
• /
• 2002.06a
• /
• pp.220-236
• /
• 2002

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

• 한국연소학회:학술대회논문집
• /
• 2015.12a
• /
• pp.313-313
• /
• 2015

• Journal of the Korean Society of Propulsion Engineers
• /
• v.18 no.4
• /
• pp.18-25
• /
• 2014

In this paper, the mechanism of the combustion instability which may occur in a hybrid rocket motor with a diaphragm was studied. And the new design for a hybrid motor grain was suggested. It could increase a regression rate of solid fuel, and reduce a large pressure oscillation in a hybrid rocket motor with a diaphragm. It was confirmed that the main mechanism of a large pressure oscillation was hole-tone, and it was caused by a collision between a diaphragm and a vortex which was generated in a pre-chamber. And 'Stepped Grain' design which had the mechanism for high regression rate in a motor with a diaphragm and could reduce a combustion instability was suggested.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.19 no.6
• /
• pp.72-80
• /
• 2015

Recently air breathing propulsion system is much interested in relatively comparing to the conventional chemical propulsion, and the R&D of this area is performed much more including the basic research of the solid ramjet in our country. The boron is applied to the solid fuel because of its high heating value, but it has a complicated combustion characteristics. therefore many researches have been studied in this area. In this paper the combustion characteristics of the boron have been investigated through the published papers for the purpose of the ramjet fuel application.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.12
• /
• pp.59-66
• /
• 2006

To understand the role of helical geometry on the regression rate enhancement, two competing underlying mechanisms such as turbulence enhancement and swirling motion production were studied by numerical calculations. Experimental results showed that the enhancement of heat transfer rate has the very close relation to the increase in regression rate even though the percentage of increase in heat transfer rate is different from that in regression rate. This discrepancy is presumably due to the change of turbulent flow feature caused by so-called "blowing mass flux" from the fuel surface. In this regard, the results of RANS calculation show that the blowing velocity is responsible for the reduction of the swirl generation and the increase in the turbulent kinetic energy. And the dominancy of one of the mechanisms causes the increase in the regression rate. Meanwhile, the increase in turbulent kinetic energy due to the mixing of blowing flow and free stream flow does not contribute for the enhancement of the heat transfer rate to the surface because the blowing flow pushes boundary layer away from the solid surface.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.2
• /
• pp.159-165
• /
• 1999

Experimental studies have been performed to observe the basic phenomena of waste bed combustion in MSW incinerator. A reduced scale apparatus was utilized to simulate the combustion behavior in real plant with 1-dimensional transient behavior at the experimental setup, which uses wet cubic wood with ash content as simulated waste. LHV (lower heating value) of solid fuel, fuel particle size and flow rate of combustion air were taken as important parameters of the bed combustion. For the quantitative analysis, FPR (flame propagation rate), TBT (total burn-out time) and PBT (particle burn-out time) was defined. LHV represent the capability of heat release of the fuel, so that a higher LHV results in faster reaction rate of the fuel bed, which is shown by higher FPR. Fuel particle size is related with surface area per unit mass as well as heat and mass transfer coefficient. As the particle size increases the FPR decreases owing to decreasing specific surface area. Air injection supplies oxygen to the reaction zone. However oversupply of combustion air increases convection cooling of the bed and possibly extinguishes the flame.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.11a
• /
• pp.91.1-91.1
• /
• 2011

고체산화물 연료전지(Solid Oxide Fuel Cell이하 SOFC)는 연료가 갖는 화학에너지를 연소과정 없이, 공기와 H2, CO, CH4와 같은 환원성 가스를 공급받아 $600{\sim}1000^{\circ}C$에서 전기화학적 반응을 통하여 직접 전기를 얻는 방식이다. SOFC는 $700^{\circ}C$ 이상의 고온에서 고체산화물이 연료와 공기가 반응하여 전기와 열을 동시에 생산하기 때문에 carnot cycle의 제한을 받지 않아 발전효율이 40% 이상으로 고효율이고, NOx 및 SOx를 배출하지 않아 무공해이며, moving parts가 없어 소음이 나지 않고, 건설과 증설이 지역이나 기후 조건에 제약 없이 용이하고, 다양한 용량이 가능하며, 고가의 백금 촉매를 사용하지 않으며, 수소, 석탄가스, 천연가스 등의 연료를 사용할 수 있는 장점이 있음, 또한 다향한 형태로 제작할 수 있으며 전해질이 고체에서 전해질 손실 및 보충에 문제가 없고 타 연료전지에 비해 개질기가 필요 없어 발전시스템이 간단하고 경량화가 가능하다. 전사법은 paste를 제작하여 전사용지에 Screen printing하여 건조 후 coating하는 방법으로 기존의 여러 coating 방법보다 제작이 용이하고 소재의 크기, 두께조절이 간편하며, 구성층의 표면조도나 굴곡에 대응이 용이한 방법이다. 본 실험에서는 paste 제조, 전사법을 이용하여 Anode, AFL, Electrolyte, CFL, Cathode전사지를 제작하고 이를 세라믹 평관형 지지체에 변수로 두께 조건별 Coating 한 후 $1400^{\circ}C$ 소결을 진행하여 SEM 분석으로 미세구조 관찰, 출력특성 및 Impedance을 확인하였다.

• 한국연소학회:학술대회논문집
• /
• 2003.05a
• /
• pp.119-127
• /
• 2003

In this study we propose an unsteady I-dimensional model of bed combustion with multiple solid phases, which confers a phase on each solid material. This model can be applied to a variety of bed combustion cases of various configurations and ignition methods. It contains fuel combustion, gaseous reaction, heat transfers between each phase, and geometric changes of the solid particles. An iron ore sintering pot is selected for verifying the model validity and simulation results are compared with the limited experimental data set of various coke contents and air supply rates. They predict the experimental results well and show applicabilities to the various system of the fuel bed with various solid materials.

• 한국연소학회:학술대회논문집
• /
• 2000.12a
• /
• pp.236-245
• /
• 2000

A laboratory scale fluidized bed reactor was developed to treat the combustion characteristics of some fuels (wood, paper sludge, refuse derived fuel). The aims were to introduce the means of experiment and interpretation of the results and finally determine the particle characteristics on the pyrolysis and combustion process of the fuel. A single particle combustion process in the fluidized bed was closely observed. Understanding experimental facility characteristics and determining parameters were also carried out. The fuel combustion processes were observed by carbon conversion rate, recovery and mean carbon conversion time. They were estimated with the CO, $CO_2$ gas concentration monitored at the exit of the combustor. Fuel drying and pyrolysis process were governed by temperature distribution in the fuel particle. There was a significant overlap of the drying and devolatilization. However, transition process from devolatilization to char combustion seemed to be determined by mechanical solidity of the fuel particle after devolatilization process.