• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.85-88
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• 2010

본 연구에서는 액체로켓 분사기에서 임계압력 이상의 추진제의 혼합과 연소과정을 수치적으로 모사하여 분석하고자 하였다. 이 과정에서 확장된 $k-{\varepsilon}$ 난류 모델을 이용하여 난류 속도장을 예측하였고 고압에서의 실제 유체 효과를 고려하기 위하여 혼합 추진제의 물성치는 SRK 상태 방정식을 이용하여 계산하였다. 또한 난류 확산 화염에서의 좀 더 정확한 난류와 화학반응의 상호작용을 고려하기 위하여 실제 유체 효과를 고려할 수 있는 층류 화염편 모델을 이용하였다. 수치적인 계산을 바탕으로 이상기체 가정을 사용한 결과와 비교하여 실제 유체의 효과와 기체메탄/액체산소 동축 전단 분사기의 제트화염 구조를 상세하게 살펴보았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1499-1504
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• 2004

Flue gas recirculation (FGR) is a method used to control oxides of nitrogen ($NO_x$) in combustion system. The recirculated flue gases resulted in slow reaction and low flame temperatures, which in turn resulted in decreased thermal NO production. Recently, it has been demonstrated that introducing the recirculated flue gas in the fuel stream, that is, the fuel induced recirculation (FIR), resulted in a much greater reduction in $NO_x$ per unit mass of recirculated gas, as compared to introducing the flue gases in air. In the present study, the effect on $NO_x$ reduction in turbulent swirl flame in laboratory scale using FGR/FIR methods through the dilution using $N_2$ and $CO_2$. Results. show the $CO_2$ dilution is more effective $NO_x$ reduction methods because of large temperature drop due to the larger specific heat $CO_2$ compared to $N_2$. FIR is more effective to reduce $NO_x$ emission than FGR when the same recirculation ratio of dilution gas.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.14-17
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• 2010

7개 스월 인젝터 연소기의 스월 방향에 따른 유동 특성을 파악하기 위하여 3차원 Large Eddy Simulation(LES)을 수행하였다. 해석에 이용된 연소기 모델은 Georgia 공대 Aerospace Combustion Laboratory의 LRE combustor를 이용하였으며, 경계 조건은 실험에서 얻어진 값을 적용하였다. 7개 인젝터의 스월 방향을 모두 동일한 방향으로 설정하였을 경우, 스월 유동간의 간섭이 증가하게 되고, 연소실 벽면에서 강한 원주방향의 속도 분포가 형성되는 것을 관찰하였다. 또한 연소실 내 압력변동폭은 인젝터의 스월 방향을 상반되게 설정하였을 때보다 현저히 증가한 것을 확인하였다.

• 센서학회지
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• 제5권6호
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• pp.43-50
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• 1996

대부분을 수입에 의존하고 있는 연료의 연소효율 증대, thermal NOx의 배출 저감은 화염특성 감지 및 분석을 통해서도 가능하다. 연소시스템에서 화영의 flicker에 대한 정보를 퓨리어 변환을 통해 frequency domain data 로 변환시켜 해석한 결과, 일반적으로 연소 영역의 난류강도가 커질수록 frequency와 강도는 커졌으며, 화염의 강도는 연료 공급 유량이 커질수록 항께 커졌다. 선회도가 $0{\sim}1.16$ 범위에서 커질 때, 화염의 강도는 작아졌다. 시험 연소로의 관찰구를 통하여 얻은 신호는 화염유무에 따라 그 차이가 매우 커서 화염의 존재 유무를 쉽게 알 수 있었다. 발생되는 NOx의 양은 화염강도와 밀접한 관계가 있음을 보여주었다.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1134-1141
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• 2003

Performance of a gas turbine combustor installed in a test facility has been studied by measuring spatially- and temporally-resolved temperature distributions using multiplex CARS technique. 500 CARS temperatures were determined at each measuring point to obtain a histogram of temperature distribution. Experiments were carried out in the aero-engine combustor sector rig burning standard kerosene fuel. The histograms were obtained around a triple-sector double annular rig running in ground idle conditions, showing features of flow mixing within the rig. The temperature histograms that prove the existence of high temperatures above 1900 K provide us valuable information to improve the design of the combustor structure suppressing NOx generation in turbulent combustion processes. The effects of swirl direction and pre-filmer on gas turbine combustion were investigated. When we installed radial swirls, a large recirculation zone was formed by the fuel module regardless of swirl directions and the pre-filmer installation. It is found that the swirl direction affects the shape of the reverse flow zone, however. Also, an attempt to estimate the flow field and flame structure is made using the histogram of temperature determined with the CARS technique.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1458-1464
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• 2002

$CO_2$ is well known greenhouse gas which is the major source of global warming. Reducing $CO_2$ emission in combustion process can be achieved by increasing combustion efficiency, oxygen enriched combustion and recirculation of the emitted $CO_2$ gas. Stability of non-premixed flame in oxygen enriched environment will be affected by the amount of oxygen, kind of diluents and fuel exit velocity. The effects of these parameters on flame liftoff and blowout are studied experimentally oxidizer coflowing burner. Experiments were divided into three cases according as where $CO_2$gas was supplied. - 1) to coflowing air, 2) to fuel with 0$_2$-$N_2$ coflow, 3) to coflowing oxygen. Flame in air coflowing case was lifted in turbulent region. Flame lift and blowout in laminar region with the increase in $CO_2$ volume fraction in $CO_2$-Air mixture makes flame lift and blowout in laminar region. Increase in oxygen volume fraction makes flame stable-i.e. flame liftoff and blowout occur at higher fuel flowrates. Liftoff height was non-linear function of nozzle exit velocity and affected by the $O_2$ volume fraction. It was found that the flame in $O_2$-$N_2$ coflow case was more stable than $O_2$-$CO_2$ case, Liftoff heights vs (nozzle exit velocity/laminar burning velocity)$^{3.8}$ has a good correlation in $O_2$-$CO_2$ oxidizer case.

• 한국추진공학회지
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• 제19권1호
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• pp.9-17
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• 2015

기본 유동 형상은 상대적으로 얇은 중간층이 연료와 공기 사이에 끼어있는 평행 2단 혼합층으로 구성되어 있다. 본 연구는 중간층의 두께 변화에 따른 연소 향상을 수치해석을 통해 조사하였다. 이 경우에, 난류 혼합층에서 열 방출에 의한 효과가 중요하다. 수치해석을 수행하기 위해 완전 보존적인 비정상 2차 시간 정확도의 하부 반복 기법과 2차 총 변화 억제 기법을 k-${\omega}$ 전단응력이동 모델이 결합된 유한체적법과 함께 사용하였다. 다음과 같이 3개의 경우에 대해 해석을 수행하였다. 연료와 공기로 구성된 단일 혼합층, 연료와 공기 사이에 불활성 기체층이 끼어있는 2단 혼합층, 그리고 연료와 공기 사이에 차가운 연료층이 끼어있는 2단 혼합층. 수치해석은 중간 기체층이 1, 2, 4 mm 인 경우에 대하여 수행되었다. 기체층의 총 두께는 4 cm이다. 불활성기체층이 2, 4 mm인 경우와 저온의 연료층이 4 mm인 경우에 단일 혼합층의 경우보다 연소영역이 확대된다.

• 한국분무공학회지
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• 제6권1호
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• pp.18-24
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• 2001

Liquid fossil fuel contaminated by water can cause trouble in the combustion processes and affect the endurance of a combustion system. Using an optical sensor to monitor the water content instantaneously in a fuel pipeline is an effective means of controlling the fuel quality in a combustion system. In two component liquid flows of oil and water, the flow pattern and characteristics of water droplets are changed with various flow conditions. Additionally, the light scattering of the optical sensor measuring the water content is also dependent on the flow patterns and droplet characteristics. Therefore, it is important to investigate the detailed behavior of water droplets in the pipeline of the fuel transportation system. In this study, the flow patterns and characteristics of water droplets in the turbulent pipe flow of two component liquids of gasoline and water were investigated using optical measurements. The dispersion of water droplets in the gasoline flow was visualized, and the size and velocity distributions of water droplets were simultaneously measured by the phase Doppler technique. The Reynolds number of the gasoline pipe flow varied in the range of $4{\times}10^{4}\;to\;1{\times}10^{3}$, and the water content varied in the range of 50 ppm to 300 ppm. The water droplets were spherical and dispersed homogeneously in all variables of this experiment. The velocity of water droplets was not dependent on the droplet size and the mean velocity of droplets was equal to that of the gasoline flow. The mean diameter of water droplets decreased and the number density increased with the Reynolds number of the gasoline flow.

• 한국화재소방학회논문지
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• 제11권1호
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• pp.21-35
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• 1997

The natural convection and combined heat transfer induced by fire in a rectangular enclosure is numerically studied. The model for this numerical analysis is partially opened right wall. The solution procedure includes the standard k-$\varepsilon$ model for turbulent flow and the discrete ordinates method (DOM) is used for the calculation of radiative heat transfer equation. In numerical study, SIMPLE algorithm is applied for fluid flow analysis, and the investigations of combustion gas induced by fire is performed by FAST model of HAZARD I program. In this study, numerical simulation on the combined naturnal convection and radiation is carried out in a partial enclosure filled with absorbed-emitted gray media, but is not considered scattering problem. The streamlines, isothermal lines, average radiation intensity and kinetic energy are compared the results of pure convection with those of the combined convection-radiation, the combined heat transfer. Comparing the results of pure convection with those of the combined convection-radiation, the combined heat transfer analysis shows the stronger circulation than those of the pure convection. Three different locations of heat source are considered to observe the effect of heat source location on the heat transfer phenomena. As the results, the circulation and the heat transfer in the left region from heating block are much more influenced than those in the right region. It is also founded that the radiation effect cannot be neglected in analyzing the building in fire. And as the results of combustion gas analysis from FAST model, it is found that O2 concentration is decreased according to time. While CO and CO2 concentration are rapidly increased in the beginning(about 100sec), but slowly decreased from that time on.

• 한국해양공학회지
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• 제27권2호
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• pp.59-68
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• 2013

Because of the recent increase in maritime cargo capacity, the production and price of crude oil have been rising. As oil prices have risen, many problems have occurred in the industry. To solve these problems, marine resources are being actively developed, and there has been an increase in the orders for special vessels and marine structures for the development of marine resources. However, consequently, various kinds of accidents have also occurred in these special vessels and structures. One of the major types of accidents involves fire and explosion, which cause many casualties and property damage. Therefore, various studies to estimate and prevent such accidents have been carried out. In this study, as basic research for the prevention of fire and explosion, numerical simulations on combustion were carried out by using a commercial grid generation program, Gridgen, and a CFD program, ANSYS-CFX. The influences of some parameters, such as the grid system, turbulence model, turbulent dissipation rate, and so on, on the simulation results were investigated, and optimum ones were chosen. It was found that the present results adopting these parameters agreed moderately well with other experimental and numerical ones.