• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.434-440
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• 2000

The atomization characteristics of air-assist atomizer which is surrounded by a coflowing airstream is investigated. The air-assist, coflow air stream had swirl imparted to them in the same direction with 45 degree's angle swillers. The fuel and air entered the combustor at ambient temperature and the combustor was operated in an unconfined environment. Diesel fuel was used for all the experiments. Drop size and mean velocity are reported for certain distances downstream from the nozzle. The droplet size and velocity measurements were performed using a two-component phase/Doppler particle analyzer and velocity profiles across the entire flowfield are presented.

• Journal of Advanced Marine Engineering and Technology
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• 제40권2호
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• pp.102-106
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• 2016

An experimental study on the flow characteristics under various laminar coflow diffusion flames was conducted with a particular focus on the buoyancy force exerted from gaseous hydrocarbon fuels. Methane ($CH_4$), ethylene ($C_2H_4$), and n-butane ($C_4H_{10}$) were used as the fuels. A coflow burner and the Schlieren imaging technique were used to observe the flow field of each fuel near the nozzle exit as well as the flow characteristics in the flames. The results show that a vortex with a density heavier than air appeared in n-butane near the nozzle exit with a strong negative buoyancy on the fuel steam. As the Reynolds number increased through the control of the fuel velocity of the n-butane flame, the vortices were greater and the vortex tips were moved up from the nozzle exit. In addition, the heated nozzle affected the flow fields of the fuel steam near the nozzle exit.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2005년도 추계학술대회 논문집
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• pp.74-79
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• 2005

The tribrachial flame in laminar coflow jet has been investigated experimentally with unsteady propagating condition. With adopting various visualization techniques, including OH-PLIF, Rayleigh Scattering technique, it was confirmed that the location of tribrachial point is on the inclined surface of flame and the propagation speed of tribrachial flame was significantly affected by the velocity gradient.

• 한국연소학회지
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• 제12권2호
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• pp.26-33
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• 2007

To reveal the newly found liftoff height behavior of hydrogen jet, we have experimentally studied the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition. The objectives of the present research are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The velocity of hydrogen was varied from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/s. For the simultaneous measurement of velocity field and reaction zone, PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. As results, it has been found that the stabilization of lifted hydrogen diffusion flames is related with a turbulent intensity, which means that combustion occurs at the point where the local flow velocity is balanced with the turbulent flame propagation velocity.

• 한국연소학회지
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• 제20권1호
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• pp.43-51
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• 2015

A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

• 대한기계학회논문집B
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• 제36권6호
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• pp.639-646
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• 2012

가열된 동축류 공기에서 일산화탄소/수소의 층류 제트에 대한 자발화된 부상화염의 특성을 조사하였다. 그 결과로 자발화가 발생하지 않는 영역에서는 제트속도의 증가에 따라 노즐부착화염에서 안정화된 층류 부상화염을 거치지 않고 바로 화염날림이 발생하였다. 자발화 영역에서, 질소 희석된 일산화탄소의 자발화된 부상화염은 산화제 내의 함유된 수분에 따른 점화지연시간의 변동으로 그 부상높이가 크게 영향을 받았다. 그리고 수소에 의한 저온 자발화 영역에서 자발화된 부상화염은 제트속도의 증가에 따라 부상높이가 감소하다가 증가하는 독특한 현상이 발생하였다. 점화지연시간에 의한 자발화된 층류 부상화염의 안정화 메커니즘을 기반으로, 그 부상높이의 거동은 점화 과정에서 발생하는 열손실의 영향뿐만 아니라 연료제트의 운동량과 질량의 선호 확산에 의하여 영향을 받을 수 있다는 것을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.529-532
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• 2002

In coflow jets with relatively large size nozzle and low fuel jet velocity, the buoyancy effect arises from the density difference between fuel and air streams. The present study investigated the behavior of such a buoyant cold Jet both numerically and experimentally, especially when the fuel stream has higher density than air. It has been demonstrated that the cold jet has a circular cone shape since upwardly injected fuel jet decelerates and forms a stagnation region, when the fuel jet was composed of propane highly diluted with nitrogen. When the fuel was moderately diluted, numerical results showed the Kelvin-Helmholtz type instability along the mixing layer of the jet. The stagnation height increases nonlihearly with fuel jet velocity with the power of approximately 1.64.

• 대한기계학회논문집B
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• 제32권3호
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• pp.190-197
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• 2008

It was experimentally studied that the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition to reveal the newly found liftoff height behavior of hydrogen jet. The objectives are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The hydrogen jet velocity was changed from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/s. For the simultaneous measurement of velocity field and reaction zone, PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. As a result, it was found that the stabilization of lifted hydrogen diffusion flames is correlated with a turbulent intensity and Karlovitz number.

• 한국연소학회지
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• 제22권4호
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• pp.43-50
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• 2017

In this study, the multi-environment probability density function(MEPDF) approach has been applied to numerically investigate Delft-Jet-in-Hot-Coflow(DJHC) turbulent flames under Moderate or Intense Low-oxygen Dilution (MILD) combustion condition. Computations are made for two different jet velocities(Re = 4100 and 8800). In terms of mean axial velocity, temperature, and turbulent kinetic energy, numerical results are in reasonably good agreements with experimental data even if there exist the noticeable deviations in downstream region. Based on numerical results, the detailed discussions are made for the essential features of the non-visible flame structure and MILD combustion processes.

• 한국항공우주학회지
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• 제36권4호
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• pp.352-356
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• 2008

수소제트와 동축공기를 사용한 본 연구에서, 난류확산화염의 화염안정성 특징을 실험적으로 수행하였다. 목적은 연료속도 증가에 따라 감소하는 부상화염길이의 경향을 보고하고, 부상 메커니즘을 포함한 화염구조를 분석하는 것이다. 수소연료는 100에서 300 m/s 사이에서 조절되었으며, 이때 동축공기는 16 m/s 고정되고, 주위류는 0.1 m/s 이하로 유지되었다. 유동장과 연소장 동시측정을 위하여, 두 대의 Nd:Yag 레이저와 CCD 카메라를 이용하여 PIV와 OH PLIF 기법이 사용되었다. 결론적으로 난류화염전파속도는 난류강도에 비례하였으며, 제트 레이놀즈수의 0.017승에 비례하였다.