• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.93-98
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• 2007

스크램제트의 연소실 내부로 유입되는 공기의 속도는 초음속으로 체류 시간은 수 ms로 매우 짧다. 이 짧은 시간 안에 연료분사, 공기-연료 혼합, 연소과정이 모두 이루어져야 한다. 공기와 연료의 혼합을 증대하는 방법은 여러 가지가 제시되었다. 이중 자유류 마하수 2.5의 단일 수직 분사 방법에서의 Cavity를 이용한 혼합 특성올 알아보기 위해 수치해석을 수행하였다. 사용된 코드는 동일조건의 실험결과와 비교하여 검증하였고 이를 통해 Cavity의 크기에 의한 혼합증대를 확인할 수 있었다.

• 한국자동차공학회논문집
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• 제12권5호
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• pp.19-24
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• 2004

Entrainment of ambient gas into a transient diesel spray is a crucial factor affecting the following preparation of combustible mixture. In this study, the entrainment characteristics of ambient gas for a non-evaporating transient diesel were investigated using a common-rail injection system. The effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient. Laser Doppler Velocimetry (LDV) technique was introduced to measure the entrainment speed of ambient gas into a spray. There appeared a region where the entrainment coefficients remained almost constant while injection rates were still changing. The effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. Entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density was greater than that of turbulent jet whose entrainment coefficient remained constant. The non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. The mean value of entrainment coefficient was found to increase with non-dimensional distance from the nozzle tip, which would be suggested as the guideline for the nozzle design.

• 한국화재소방학회논문지
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• 제19권3호
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• pp.58-63
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• 2005

등유 풀화재의 화염과 연소에 의해 생성되는 연기의 특성에 대해서 조사하였다. 다양한 발열량을 위해 직경을 변하게 할 수 있는 팬버너를 제작하였다. 풀화재를 조사하기 위해 화염 높이와 떨림 주파수를 분석하였다. 실험적으로 풀화염 높이는 이론적 상관관계 증가율과 잘 일치하지만, 정량적으로는 등유의 연소율에 기인하여 과대 평가된 값을 보인다. 연기의 특성을 조사하기 위해 세 가지의 실험방법을 사용하였다. 먼저 가스분석기를 이용하여 연소시 발생되는 주요 가스 농도를 측정하였는데 이산화탄소의 생성과 산소의 소모율은 풀화염의 열방출율에 비례하지만, 일산화탄소의 발생에 대한 경향성은 발견할 수 없었다. 연기의 매연입자를 광감쇄법과 TEM 이미지를 이용하여 특성을 조사하였다 연기밀도는 발열량의 증가에 따라 매우 급격히 증가하였고, 등유 풀화염에서 발생한 매연입자들은 자연적인 연소조건임에도 불구하고 역확산 제트화염에서 생성된 매연과 유사한 형태와 탄화정도를 보임이 관찰되었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.81-86
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• 2007

스크램제트의 연소실 내부로 유입되는 공기의 속도는 초음속으로 체류 시간은 수 ms로 매우 짧다. 이 짧은 시간 안에 연료분사, 공기-연료 혼합, 연소과정이 모두 이루어져야 한다. 공기와 연료의 혼합을 증대하는 방법은 여러 가지가 제시되었다. 이중 자유류 마하수 2.5의 단일분사 방법에서의 cavity를 이용한 혼합증대 특성을 알아보기 위해 수치해석을 수행하였다. 사용된 코드는 동일조건의 실험결과와 비교하여 검증하였고 이를 통해 Cavity에 의한 혼합증대 특성을 확인할 수 있었다.

• 한국수소및신에너지학회논문집
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• 제25권1호
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• pp.59-71
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• 2014

An experimental study has been conducted to investigate the heat transfer characteristics of laminar syngas/air mixture with 10% hydrogen content impinging normally to a flat plate of cylinder. Effects of impinging distance, Reynolds number and equivalence ratio as major parameters on heat fluxes of stagnation point and radial direction were examined experimentally by the direct photos and data acquisitions from heat flux sensor. In this work, we could find the incurved flame behavior of line shaped inner top-flame in very closed distance between flat plate and burner exit, which has been not reported from general gas-fuels. There were 3 times of maximum and 2 times minimum heat flux of stagnation point with respect to the impinging distance for the investigation of Reynolds number and equivalence ratio effect. It was confirmed that the maximum heat flux of stagnation point in 1'st and 2'nd peaks increased with the increase of the Reynolds number due to the Nusselt number increment. There was a third maximum rise in the heat flux of stagnation point for larger separation distances and this phenomenon was different each for laminar and turbulent condition. The heat transfer characteristics between the stagnation and wall jet region in radial heat flux profiles was investigated by the averaged heat flux value. It has been observed that the values of averaged heat flux traced well with the characteristics of major parameters and the decreasing of averaged heat flux was coincided with the decreasing trend of adiabatic temperature in spite of the same flow condition, especially for impinging distance and equivalence ratio effects.

• 한국응용과학기술학회지
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• 제30권2호
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• pp.320-332
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• 2013

소각로 내 공기 주입은 연소가스의 체류시간, 미연분 제거 및 출구가스 온도 제어 등의 많은 영향을 끼친다. 이에 따라 2차 연소용 공기량을 변화시켜 충분한 체류시간을 확보하고 $850^{\circ}C$ 이상의 출구가스 온도를 유지하며, 높은 turbulent를 관리함으로써 안정적인 소각로 운영이 되어야만 한다. 본 연구에서는 현재 운영 중인 소각장의 소각로를 설계하고, 평균 일일 소각량을 바탕으로 1차 공기량을 산정한 후 2차 공기량을 변화하여 CFD 프로그램(Fluent)을 통해 이론적인 공기유동을 규명하였다. 또한 산정된 공기량을 바탕으로 실제 운영 중인 소각장에 적용함으로써 최적의 연소조건을 도출하였다. CFD simulation 결과 1.2차 공기비는 75:25가 최적의 결과로 나타났으며, 2차 공기 분사노즐 전 후면 유속 비는 1:3에서 가장 우수한 결과로 나타났다. 또한, 실제 운영 중인 소각로에 적용한 결과 적절한 소각로 출구온도는 질소산화물 제거 효율 및 일산화탄소 발생농도에 영향을 미치는 것으로 나타났다.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2386-2396
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• 1996

본 연구에서 수행한 큰 지름비를 가지는 동축제트 확산화염 연소기내의 등온 및 연소 유동장에 대한 수치해석 결고를 요약하면 다음과 같다. 1) 큰 지름비를 가지는 동축제트 확산화염 연소기내의 등온 유동을 수치해석한 경우 k-.epsilon. 난유모델은 큰지름비를 갖는 기하학적 특성 때문에 C $O_{2}$와 공기의 유량비에 따라 나타나는 세가지 유동구조를 정성적으로 잘 예측하였다. 2) 공기의 유량이 고정되고 C $O_{2}$의 유량이 증가하는 등은 유동의 경우, 후방정체점은 실험치보다 훨씬 과도하게 예측되고 있으나, C $O_{2}$의 유량증가와는 거의 무관하게 나타나는 실험결과를 그대로 반영하였다. 그리고 C $O_{2}$으 유량증가에 거의 선형적으로 비례하는 전방정체점의 위치와 급격히 감소하는 재순환유동영역으로 갈수록 정량적인 불일치가 커지게 됨을 볼 수 있으며 이는 연료제트의 속도척도가 상대적으로 커지면서 연료제트가 공기의 재순환유동을 간헐적으로 뚫고 나가며 나타나는 용접유동구조에 의한 비정상성 때문으로 사료된다. 3) C $O_{2}$의 유량이 고정되고 공기의 유량이 증가하는 등온유동의 경우, 전방정체점의 변화에 대한 실험과 수치해석 결과와 정량적인 일치를 보이고 있으나 후방정체점은 실험치에 비해 과대예측되었다. 공기의 평균유입속도가 증가함에 따라 전방정체점의 위치가 입구쪽으로 옮겨가는 경향을 나타내고 있으며 공기의 유량이 증가함에 따라 공기에 이한 재순환영역의 강도와 공기의 최대역류속도가 커지므로 상대적으로 C $O_{2}$ 제트가 재순환 유동장을 관통할 수 있는 거리가 즐어드는 현상을 잘 예측하였다. 4) k-.epsilon. 난류모델과 수정된 eddy-breakup 연소모델을 사용하여 bulff-body 연소기내의 연소유동을 수소에 의한 열팽창효과를 포함시킨 경우 유동장과 온도장이 약간 더 하류족으로 팽창되는 영향이 나타났으며 본 연구의 수치결과만을 놓고 볼 때 열팽창효과와 Arrhenius 화학반응률을 고려한 경우가 실험치에 다소 근접한 결과를 나타내었다. 5) 수치결과와 실험의 불일치는 등방성 가정에 근거를 두는 k-.epsilon.난류모델이 갖는 한계, 중간생성물을 무시한 일단계 비가역반응모델을 사용한 난류 연소모델의 한계, 밀도변화를 가지는 유동장에서 일정한 Schmisr 수 가정의 적용한계, 그리고 불확실한 입구경계조건에 기인한다. bluff-body 연소기내의 난류연소유동장에 대한 예측능력을 향상시키기 위해서 추후 연구에서는 더욱 발전된 물리모델인 ASM 난류모델과 RSM 난류모델 그리고 joint PDF 연소모델과 coherent flamelet 모델등을 이용한 수치모델의 개발을 체계적으로 수행할 예정이다.

• 설비공학논문집
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• 제12권12호
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• pp.1098-1125
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• 2000

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 1998 and 1999 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. 1) A review of the recent studies on fluid flow, turbomachinery and pipe-network shows that many experimental investigations are conducted in applications of impingement jets. Researches on turbulent flows, pipe flows, pipe-networks are focused on analyses of practical systems and prediction of system performance. The results of noise reduction in the turbomachinery are also reported. 2) A review of the recent studies on heat transfer analysis and heat exchanger shows that there were many papers on the channel flow with the application to the design of heat exchanger in the heat transfer analysis. Various experimental and numerical papers on heat exchanger were also published, however, there were few papers available for the analysis of whole system including heat exchanger. 3) A review of the recent studies on heat pump system have focused on the multi-type system and the heat pump cycle to utilize treated sewage as the heat source. The defrosting and the frosting behaviors in the fin-tube heat exchanger is experimentally examined by several authors. Several papers on the ice storage cooling system are presented to show the dynamic simulation program and optimal operation conditions. The study on the micro heat pipes for the cooling of high power electronic components is carried out to examine the characteristics of heat and mass transfer processed. In addition to these, new type of separate thermosyphon is studied experimentally. 4) The recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. New systems operating with natural refrigerants are drawing lots of attention. In addition to these, evaporation and condensation heat transfer characteristics of traditional and new refrigerants are investigated for plain tubes and also for microfin tubes. Capillary tubes and orifice are main topics of research as expansion devices and studies on thermophysical properties of new refrigerants and refrigerant/oil mixtures are widely carried out. 5) A review of the recent studies on absorption cooling system shows that numerous experimental and analytical studies on the improvement of absorber performance have been presented. Dynamic analysis of compressor have been performed to understand its vibration characteristics. However research works on tow-phase flow and heat transfer, which could be encountered in the refrigeration system and various phase-change heat exchanger, were seemed to be insufficient. 6) A review of recent studies on duct system shows that the methods for circuit analysis, and flow balancing have been presented. Researches on ventilation are focused on the measurement of ventilation efficiency, and variation of ventilation efficiency with ventilation methods by numerous experimental and numerical studies. Furthermore, many studies have been conducted in real building in order to estimate indoor thermal environments. Many research works to get some information for cooling tower design have been performed but are insufficient. 7) A review on the recent studies on architectural thermal environment and building mechanical systems design shows that thermal comfort analysis is sitting environment, thermal performance analysis of Korean traditional building structures., and evaluation of building environmental load have been performed. However research works to improve the performance of mechanical system design and construction technology were seemed to be insufficient.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.1-2
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• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.