• 대한기계학회논문집B
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• 제30권9호
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• pp.891-897
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• 2006

The SRS method is applied to a turbulent flame with radiation/turbulence interaction to invert the temperature and concentration profile. The flame is conditioned as optically thin per each fluctuation length and the flame spectral intensity is measured for inversion. From inversion result, we find that SRS can successfully invert the coupled temperature/concentration fluctuation amplitudes. For two cases of experiments, inverted values are within approximately 1% over the full range of fluctuation amplitude. However, SRS cannot find the detailed local fluctuation parameters such as pattern and phase, etc. as far as they do not affect the resulting radiation intensity. Important available parameters are the mean temperature and the temperature fluctuation amplitude. The radiation/turbulence interaction effect is verified to play an important role in the radiation.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.133-138
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• 2007

Influence of changing combustor pressure on flame stabilization and emission index in the swirl-stabilized flame was investigated The combustor pressure was controlled by suction fan at combustor exit. Pressure index ($P^{\ast}=P_{abs}/P_{atm}$), where $P_{abs}$ and $P_{atm}$ indicated the absolute pressure and atmosphere pressure, respectively, was controlled in the range of $0.7{\sim}1.3$ for each equivalence ratio conditions. The flammable limits of swirl flames were largely influenced by changing combustor pressure and they showed similar tendency with laminar flames. $NO_x$ emission index decreased with decreasing pressure index for overall equivalence ratio conditions. R.m.s. of pressure fluctuations is increased with decreasing combustor pressure. This flame fluctuation caused incomplete combustion , hence CO emission index increased. These oscillating flames were measured by simultaneous $CH{\ast}$ chemiluminescence time-series visualization and pressure fluctuation measurement.

• 한국연소학회지
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• 제10권2호
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• pp.35-41
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• 2005

Behaviors of lean premixed flame of propane/air and methane/air flame anchored by a pilot flame in a tube were investigated experimentally varying the mean velocity from 10 to 140 cm/s and the equivalence ratio from 0.45 to 0.8. Behaviors of both flames are divided into five regions of stable, flash-back, tail-out, flickering and vibrating. General characteristics of each region and Le number effect are investigated. Two main instabilities, flickering and vibration, are both unstable but the instability mechanism, the frequency and the amplitude of pressure fluctuation are different. In the edge of the vibrating region, pressure fluctuation repeats generation and extinction. Repeated growth and decrease of the amplitude of pressure fluctuation are explained by Rayleigh#s index.

• 대한기계학회논문집B
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• 제34권2호
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• pp.197-202
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• 2010

자발 진동하는 층류 예혼합 분젠 화염을 관찰하기 위하여 분기관을 가진 연소기를 제작 하였다. 특히, 조건에 따른 화염 거동을 살펴봤으며, 화염 표면적과 열발생 변동의 관계에 대하여 고찰하였다. 본 연구에서 사용된 당량비는 1.1 이고, 노즐 출구 평균 유속은 1.75 m/sec 이다. 연소 챔버와 분기관의 길이비(L.R.)는 연소기 내 압력 변동에 영향을 미치며, 결과적으로 화염 거동 특성이 달라짐을 관찰하였다. 또한, 간섭 필터의 유무에 따른 $OH^*$, $CH^*$, 그리고 화염 자발광은 정성적으로 유사한 거동을 나타냈으며, 자발 진동하는 층류 예혼합 분젠 화염의 화염 표면적 변동과 열발생 변동은 선형적인 관계를 가짐을 확인하였다.

• 대한기계학회논문집B
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• 제32권6호
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• pp.413-420
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• 2008

The unsteady heat release characteristics play a significant role in combustion instabilities observed in low emissions gas turbine combustors. Such combustion instabilities are often caused by coupling mechanisms between unsteady heat release rates and acoustic perturbations. A generalized model of the turbulent flame response to acoustic perturbations is analytically formulated by considering a distributed heat release along a curved mean flame front and using the flame's kinematic model that incorporates the turbulent flame development. The effects of the development of flame speed on the flame transfer functions are examined by calculating the transfer functions with a constant or developing flame speed. The flame transfer function due to velocity fluctuation shows that, when a developing flame speed is used, the transfer function magnitude decreases faster with Strouhal number than the results with a constant flame speed at low Strouhal numbers. The flame transfer function due to mixture ratio fluctuation, however, exhibits the opposite results: the transfer function magnitude with a developing flame speed increases faster than that with a constant flame speed at low Strouhal numbers. Oscillatory behaviors of both transfer function magnitudes are shown to be damped when a developing flame speed is used. Both transfer functions also show similar behaviors in the phase characteristics: The phases of both transfer functions with a developing flame speed increase more rapidly than those with a constant flame speed.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.128-134
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• 2006

A characterization of turbulent reacting flows has proved difficult owing to the complex interaction between turbulence, mixing, and combustion chemistry. There are many types of time scales in turbulent flame which can determine flame structure. This counter jet type premixed burner produces high intensity turbulence. The goal is to gain better insights into the flame structures at high turbulence. 6 propane/air flames gave been studied with high velocity fluctuation in bundle type nozzle and in one hole type nozzle. By measuring velocity fluctuation, turbulent intensity and integral length scale are obtained. And sets of OH LIF images were processed to see flame structure of the mean flame curvatures and flame lengths for comparison with turbulence intensity and turbulent length scales. The results show that the decrease in nozzle size generates smaller flow eddy and mean curvatures of the flame fronts, and a decrease in Damkohler number estimated from flow time scale measurement.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1166-1171
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• 2004

The combustion instability acts as a serious obstacle for the lean premixed combustion of gas turbine and even causes the fatal damage to the combustor and whole system. In this experiment, the pressure fluctuation is highly related to the stabilizing position of flame and fuel injection location. The fuel injection location is connected with the convection time of the fresh mixture, which is important time scale to refresh the mixtures near the flame stabilization location. The flame is extremely unstable when the alternative stabilization occurs and bulk mode frequency (${\sim}10Hz$) of pressure fluctuation is observed in this condition. It was found that the convection time scale of the fresh reactant coincided with the time scale of the bulk mode fluctuation. Hence this phenomenon results from the local equivalence ratio change caused by the pressure fluctuation induced by thermo-acoustic effects.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2007년도 추계학술대회
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• pp.149-154
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• 2007

This study examines the effect of acoustic excitation using forced coaxial air on the flame characteristics of turbulent hydrogen nonpremixed flames. A resonance frequency was selected to acoustically excite the coaxial air jet due to its ability to effectively amplify the acoustic amplitude and reduce flame length and NOx emissions. Acoustic excitation causes the flame length to decrease by 15 % and consequently, a 25 % reduction in EINOx is achieved, compared to a flame without acoustic excitation. Moreover, acoustic excitation induces periodical fluctuation of the coaxial air velocity, thus resulting in slight fluctuation of the fuel velocity. From phase-lock PIV and OH PLIF measurement, the local flow properties at the flame surface were investigated under acoustic forcing. During flame-vortex interaction in the near field region, the entrainment velocity and the flame surface area increased locally near the vortex. This increase in flame surface area and entrainment velocity is believed to be a crucial factor in reducing flame length and NOx emission in coaxial jet flames with acoustic excitation. Local flame extinction occurred frequently when subjected to an excessive strain rate, indicating that intense mass transfer of fuel and air occurs radially inward at the flame surface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2354-2359
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• 2007

Influence of changing combustor pressure on flame stabilization and emission index in the swirl-stabilized flame was investigated. The combustor pressure was controlled by suction fan at combustor exit. Pressure index ($P^{\ast}$=Pabs/Patm), where Pabs and Patm indicated the absolute pressure and atmosphere pressure, respectively, was controlled in the range of 0.7${\sim}$1.3 for each equivalence ratio conditions. The flammable limits of swirl flames were largely influenced by changing combustor pressure and they showed similar tendency with laminar flames. NOx emission index decreased with decreasing pressure index for overall equivalence ratio conditions. R.m.s. of pressure fluctuations is increased with decreasing combustor pressure. This flame fluctuation caused incomplete combustion, hence CO emission index increased. These oscillating flames were measured by simultaneous $CH^{\ast}$ chemiluminescence time-series visualization and pressure fluctuation measurement.

• 한국연소학회지
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• 제14권4호
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• pp.48-53
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• 2009

This paper describes the forced flame response in a turbulent premixed gas turbine combustor. The fuel was premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. To impose the inlet flow velocity, a siren type modulation device was developed using an AC motor, rotating and static plates. Measurements were 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 test results showed that flame length as well as geometry was strongly dependent upon modulation frequency in addition to operating conditions such as inlet velocity. Convection delay time between the velocity perturbation and heat release fluctuations was calculated using phase information of the transfer function, which agreed well with the results of flame length measurements. Also, basic characteristics of the flame nonlinear response shown in the current test conditions were introduced.