• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.111-120
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• 2006

The fully coupled conditional moment closure(CMC) model has been developed to realistically simulate the structure of complex turbulent nonpremixed syngas flame, in which the flame structure could be considerablyl influenced by the turbulence, transport history, and heat transfer as well. In order to correctly account for the transport effect, the CMC transport equations fully coupled with the flow and mixing fields are numerically solved. The present CMC approach has successfully demonstrated the capability to realistically predict the detailed structure and the overall combustion characteristics. The numerical results obtained in this study clearly reveal the importance of the convective and radiative heat transfer in the precise structure and NOx emission of the present confined combustor with a cooling wall.

• 한국안전학회지
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• 제17권4호
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• pp.61-65
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• 2002

Nonpremixed counterflow flames at low strain rates, $ag=12s^{-1}$ and $12s^{-1}$, were numerically simulated to investigate the effects of the duct thickness on the flame structure in normal gravity. For small values of the duct thickness, the positions of the flame and stagnation point were highly sensitive to the duct thickness. When the duct thickness was greater than 6mm, however, the effects of the duct thickness on the flame structure were negligible. The computed temperature along the duct centerline agreed well with measurements.

• 한국가스학회지
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• 제12권4호
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• pp.21-28
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• 2008

삼지화염과 포와젤(Poiseuille) 및 균일분포 연료출구 속도에 따른 부상화염의 부상거동 그리고 화염면 부근에서의 연소 유동 특성에 대하여 수치적 해석을 수행하였다. 부상화염에 대한 수치해석으로 기존 연구 결과를 검정하고 화염대 부근에서 구조적 특성을 살펴보며 포와젤 및 균일분포 연료출구속도 조건에서 운동량 유속으로 부상높이를 일반화하여 비교하였다. 또한 화염면 부근에서 속도, 압력, 온도, 화학반응속도 등으로 연소 유동 특성을 분석하고 규명하였다. 특히 중심선을 따른 속도 변화의 경우 노즐에서 화염대 부근까지는 전형적인 비반응제트 유동에 따른 속도 분포를 형성하지만 화염대 직전에서 속도가 급격히 감소하다가 화염대를 지나면서 급격히 증가한 후에 다시 감소하는 현상을 규명하였다. 화염대 전의 유동영역에서는 화염대가 장애물역할을 하다가 화염대를 지나고 나면 유동을 가속시켜주는 역할을 하고 있기 때문이다. 이러한 현상은 기존의 비반응 제트 유동으로 규명하지 못하였던 것이다.

• 한국연소학회지
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• 제13권2호
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• pp.1-6
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• 2008

An experimental study of the flame response in a turbulent premixed combustor has been conducted with room temperature, atmospheric pressure inlet conditions using premixed natural gas. The fuel is premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. Therefore the observed flame response is only the result of the imposed velocity fluctuations, which are produced using a variable speed siren. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function as a function of the modulation frequency. Of particular interest is the effect of flame structure on the flame response predictions and measurements. The results show that both the gain and the phase of flame transfer function are closely associated with the flame length and structure, which is dependent upon the upstream flow perturbation as well as equivalence ratio in the current study.

• Journal of Advanced Marine Engineering and Technology
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• 제30권8호
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• pp.853-862
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• 2006

The present study is numerically investigated the flame structure of non-premixed counterflow jet flames using the laminar flamelet model Detailed flame structures with the fuel composition of 40% CO, 30% $H_2$. 30% $N_2$ and an oxidizer composition of 79% $N_2$ and 21% $O_2$ in a non-premixed counterflow flame are studied numerically. This study is aimed to investigate the effects of axial velocity gradient and combustion atmosphere pressure on flame structure. The results show that the role of axial velocity gradient on combustion processes is globally opposite to that of combustion atmosphere pressure. That is, chemical nonequilibrium effects become dominant with increasing axial velocity gradient, but are suppressed with increasing ambient pressure. Also, the flame strength is globally weakened by the increase of axial velocity gradient but is augmented by the increase of ambient pressure. However, flame extinction is described better on the basis of only chemical reaction and in this study axial velocity gradient and ambient pressure play a similar role conceptually such that the increase of axial velocity gradient and ambient pressure cause flame not to be extinguished and extend the extinction limit, respectively. Consequently it is suggested that a combustion process like flame extinction is mainly influenced by the competition between the radical formation reaction and the third-body recombination reaction.

• 한국연소학회지
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• 제8권3호
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• pp.38-48
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• 2003

OH, CH and NO radical distributions have been measured and compared with the numerical analysis results in methane/air partially premixed laminar flames using 2-D LIF technique. The pick intensity of OH LIF signal is insensitive to fuel equivalence ratio: however, CH LIF intensity decreases as equivalence ratio increases and the NO concentration increases with equivalence ratio. The contribution of the prompt NO, formed near premixed reaction zone, to the total NO formation is evident from the OH, CH, and NO PLIF images in which the dilution effect of nitrogen is minimal for the highest equivalence ratio. Measured OH and NO LIF signals in counterflow flames agree with the computed concentration distributions. Both numerical and experimental results indicate that the structural change in a flame alters the NO formation characteristics of a partially premixed counterflow flame. The nitrogen dilution also changes flame structure, temperature and OH radical distributions and results in the decreased NO concentrations in a flame. The levels of decrease in NO concentrations, however, depends on the premixedness(${\alpha}$) of a flame. The larger change in the flame structure and NO concentrations have been observed in a premixed flame(${\alpha}=1.0$), which implies that the premixedness is likely to be a factor in the dilution effect on NO formation of a flame.

• 대한기계학회논문집B
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• 제26권1호
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• pp.125-132
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• 2002

An experimental study on the characteristics of stability of propane turbulent nonpremixed jet flames discharged normal to air free-streams with uniform velocity profile is conducted. Experimental observations are focused on the flame shape, the stability considering two kinds of flame, lift-off distance, and the flame length according to velocity ratio. In order to investigate the mixing structure of the flame base at the lower limit, we employ the RMS technique and measure the species concentration by a gas chromatography. In the results of the stability curve and lifted flame, it is fecund that the dependency of nozzle diameter is closely related to the large-scale vortical structure representing counter-rotating vortices pair. Also, the detailed discussion on the phenomenon of blowout due to this large vortical motion, is provided.

• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.391-398
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• 2005

In this investigation, turbulent premixed combustion and flame front propagation in a gas turbine combustion chamber is studied. Direct numerical simulation of turbulent reacting flows demands extremely high computational resources, especially in more complicated geometry. The alternative choice may be left for Large Eddy Simulation (LES) by which only large scales are solved directly. In combustion problems, capturing the large scales' behavior without solving the details of small scales is a difficult task. Using a transport equation for description of the flame front propagation and therefore avoiding the calculation of inner flame structure is the basic idea of this study. For this purpose. the so-called G-equation has been used by which any iso-level of the G variable provides the flame location. A comparison with the experiment indicates that the present method can predict a turbulent velocity field and also capture a instantaneous 3-dimensional flame structure.

• Journal of Advanced Marine Engineering and Technology
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• 제10권3호
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• pp.107-118
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• 1986

The presenet research attempts to examine the combustion characteristics and the structure of the flame in turbulent premixed flames and thus enhance the combustion performance that leads to the design of the effective combustion system (untilizing LNG). Following experimental investigations for several stabilized premixed flames were attempted to identify the interactive mechanism between flame structures and flow fields; Visualization by Schlieren method, measurement of flow velocity by LDV, detection of ion current by ion probe, measurement of fluctuating temperature by thermocouple having compensation circuit, average values with respect to time of fluctuating amount for flow velocity, temperature, ion current, etc., variable RMS values, PDFs, autocorrelation, crosscorrelation, spatial macroscale, power spectra, and velocity scale. Continuing the authors published studies whose flame dominated by coherent structures and the characteristics of combustion reaction for irregular three dimensional flame and stabilized flame by step were investigated with obtained experimental quantities. Results of this research are following : The most turbulent flames support the structure of a Wrinkled laminar flame or laminar flamelets. It also observed that combustion reaction is related to small tubulence microscales of the turbulent flow fields closly.

• 동력기계공학회지
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• 제2권2호
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• pp.13-19
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• 1998

The purpose of study is to investigate the flame stability and Structure of turbulent diffusion flame behind the hollowed flame holder, which is located on the waste gas coming out from the test furnace. Fluctuating temperature and ion current measurement and their statistical treatment were used for the purpose. Three types of flame were stabilized and each of which were changed by adequate equivalence ration. And we found that have no periodicity near reacting zone.