• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2000년도 제20회 KOSCO SYMPOSIUM 논문집
• /
• pp.133-141
• /
• 2000

The present study is focused on modeling the transient behavior of the local flame structure which is especially important for slow reaction processes, such as NOx formation in the radiating flame field. The recently developed unsteady flamelet model has been applied to analyze a steady, turbulent jet flame. Numerical results are compared with experimental data and numerical results of the conventional steady flamelet model. The numerical result reveals that the unsteady flamelet model correctly predicts the nonequilibrium effect upsteam and the subsequent decay of the superequilibrium radical concentrations the further downstream.

• 한국분무공학회지
• /
• 제6권3호
• /
• pp.8-16
• /
• 2001

The present study is focused on modeling the transient behavior of the local flame structure which is especially important for slow reaction processes, such as NOx formation in the radiating flame field. The unsteady flamelet model recently developed has been applied to analyze a steady, turbulent jet flame. Numerical results are compared with experimental data and numerical results of the conventional steady flamelet model. The numerical result reveals that the unsteady flamelet model correctly predicts the nonequilibrium effect upsteam and the subsequent decay of the superequilibrium radical concentrations further downstream.

• 대한기계학회논문집B
• /
• 제23권2호
• /
• pp.175-184
• /
• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• Journal of Advanced Marine Engineering and Technology
• /
• 제35권4호
• /
• pp.397-405
• /
• 2011

친환경 대체에너지의 한 분야인 수소에너지는 물의 전기분해와 화석연료의 개질을 통해 얻어 진다. PEMFC용 개질기에 적용 가능한 난류예혼합 방식의 메탈화이버 플랫버너를 제작하였다. 공급열 량에 따른 연소영역의 평균온도분포와 CO, HC, $CO_2$ 및 $O_2$등 각종 화학종의 평균농도로 플랫버너의 화염구조 및 특성을 조사하여 개질기 적용 가능성을 확인하였다. 그리고 PIV 유동실험결과와 유동수 치해석 결과를 비교 분석하여 차후 PEMFC용 개질기 개발에 있어 수치해석을 적용하기 위한 기초연구를 진행하였다.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
• /
• pp.242-250
• /
• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• 한국연소학회지
• /
• 제13권1호
• /
• pp.31-43
• /
• 2008

Oxy-fuel flame has a significantly different structure from that of air-fuel flame because of its high temperature. This study is aimed to find out the difference of the oxy-fuel flame structure in order to understand reaction mechanism closely, which is crucial to design real-scale oxy-fuel combustion system. By examining pictures of counterflow flame and LIF images, we found that oxy-fuel flame had two-zone structure: fuel decomposition region and distributed CO oxidation region. In the oxy-fuel flame, OH radical was distributed intensely through the whole flame due to its higher flame temperature than crossover temperature. For showing those features of the oxy-fuel flame, 1 MW scale IFRF oxy-natural gas burner was simulated by conditional moment closure(CMC) model. Calculation results were compared with experimental data, and showed agreements in trend. In the simulated distributions of fuel decomposition/CO oxidation rates, CO oxidation region was also separated from fuel decomposition zone considerably, which showed the two-zone structure in the oxy-fuel flame.

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

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
• /
• pp.305-313
• /
• 2005

Measurements of flame length, width and NOx emissions have been conducted to investigate the effect of an acoustic excitation on flame structure in turbulent hydrogen diffusion flames with coaxial air. The resonance frequency of oscillations was varied between 259 ,514 and 728 Hz with power rate of 0.405 and 2.88w. When these frequencies imposed to hydrogen flames, dramatic reduction of flame length and NOx emission was achieved. And acetone planar laser-induced fluorescence technique was used to measure a concentration of the near field of driven axisymmetric jet. The air-fuel stoichiometric line was plotted to investigate the mixing layer and development of air entrainment to fuel jet. Consequently, acoustic excitation on flame could enhance the air-fuel mixing resulting in abatement of NOx emission quantitatively.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
• /
• pp.211-213
• /
• 2014

Simultaneous measurements of planar laser-induced fluorescence (PLIF) of OH radicals and particle image velocimetry (PIV) were used to investigate the strain rates and OH structure characteristics of turbulent syngas non-premixed jet flames close to blowoff. Mean values of the maximum principal strain rate on OH layer decreases with the axial distance, and its standard deviation is significantly large upstream. Strain rate on stabilization region of the stable flame is only about a half of that of the flame near blowoff.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2012년도 제44회 KOSCO SYMPOSIUM 초록집
• /
• pp.201-202
• /
• 2012

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine were numerically investigated. Location of pilot nozzle, angle and direction of swirl vane were varied as main parameters with constant fuel flow rates for each nozzle. As a result, the variation in location of pilot nozzle resulted in significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus flame stability and emission characteristics might be significantly changed. The swirl angle of $45^{\circ}$ provided similar recirculating flow patterns in a wide range of equivalence ratio (0.5~1.0). Compared to the co-swirl flow, the counter-swirl flow leaded to the reduction in CTRZ and fuel-air mixing near the burner exit and a weak interaction between the pilot partially premixed flame and the lean premixed flame. With the comparison of experimental results, it was confirmed that the case of co-swirl flow and swirl $angle=45^{\circ}$ would provided an optimized combustor performance in terms of flame stability and pollutant emissions.