• 한국연소학회지
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• 제18권4호
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• pp.29-36
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• 2013

Numerical study was conducted to clarify effects of added $CO_2$ for the downstream interaction between $H_2$-air and CO-air premixed flames in counterflow configuration. The reaction mechanism adopted was Davis model which had been known to be well in agreement with reliable experimental data. The results showed that both lean and rich flammable limits were reduced. The most discernible difference between the two with and without having $CO_2$ addition into $H_2$-air and CO-air premixtures was two flammable islands for the former and one island for the latter at high strain flame conditions. Even a small amount of $H_2$, in which $H_2$-air premixed flame cannot be sustained by itself, participates in CO oxidation, thereby altering the CO-oxidation reaction path from the main reaction route $CO+O_2{\rightarrow}CO_2+O$ with a very long chemical time in CO-air flame to the (H, O, OH)-related reaction routes including $CO+OH{\rightarrow}CO_2+H$ with relatively short chemical times. This intrinsic nature alters flame stability maps appreciably. The results also showed that chemical effects of added $CO_2$ suppressed flame stabilization. Particularly this phenomenon was appreciable at flame conditions which lean and rich extinction boundary was merged. The detailed discussion of chemical effects of added $CO_2$ was addressed to the present downstream interaction.

• 한국연소학회지
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• 제20권1호
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• pp.6-14
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• 2015

Numerical study was conducted to clarify effects of added $H_2O$ for the downstream interaction between $H_2$-air and CO-air premixed flames in counterflow configuration. The reaction mechanism adopted was Davis model which had been known to be well in agreement with reliable experimental data. The results showed that both lean and rich flammable limits were reduced in increase of strain rate. The most discernible difference between the two with and without having $H_2O$ and/or $H_2$ addition into $H_2$-air and CO-air premixtures was two flammable islands for the former and one island for the latter at high strain flame conditions. Even a small amount of $H_2$, in which $H_2$-air premixed flame cannot be sustained by itself, participates in CO oxidation, thereby altering the CO-oxidation reaction path from the main reaction route $CO+O_2{\rightarrow}CO_2+O$ with a very long chemical time in CO-air flame to the OH-related reaction routes including $CO+OH{\rightarrow}CO_2+H$ with very short chemical times. This intrinsic nature alters flame stability maps appreciably. The results also showed that chemical effects of added $H_2O$ help lean flames at relatively low strain rate be sustained, and suppress the flame stabilization at high strain rates.

• 한국분무공학회지
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• 제28권1호
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• pp.24-31
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• 2023

In this study, characteristics of a propane-air premixed flame sin DC electric field was investigated. The stainless steel Bunsen burner and the stainless steel ring were used as electrode, and the high voltage supply was used for applying electric field. Flammability range increased significantly when the positive voltage was applied because of extension of LBO limit, while it shrank when the negative voltage was applied. The reason for this was not much related to the burning velocity, but the induced flow around the burner by electric field. withNOx production slightly increased after positive voltage was applied in identical equivalence ratio. Nevertheless, it was advantageous to apply the positive electric field to reduce the NOx since the extension of LBO limit makes the burner possible to operate in very low equivalence ratio.

• 한국연소학회지
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• 제6권2호
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• pp.29-35
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• 2001

Unsteady numerical study has been conducted on combustion dynamics of a lean-premixed swirl-stabilized gas turbine swirl injector. A three-dimensional computation method utilizing the message passing interface (MPI) parallel architecture, large eddy simulation(LES), and proper orthogonal decomposition (POD) technique was applied. The unsteady turbulent flame dynamics are simulated so that the turbulent flame structure can be characterized in detail. It was observed that some fuel lumps escape from the primary combustion zone, and move downstream and consequently produce hot spots. Those flame dynamics coincides with experimental data. In addition, basis modes of the unsteady turbulent flame are characterized using proper orthogonal decomposition (POD) analysis. The flame structure based on odd basis modes is apparently larger than that of even ones. The flame structure can be extracted from the summation of the basis modes and eigenvectors at any moment.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.113-114
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• 2015

In this study, 1D and 3D thermoacoustic analysis model were developed in order to predict fundamental characteristics of combustion instability in a gas turbine lean premixed combustor. The 1D network model can be used to analyze frequency and growth rate of combustor instability by simply dividing whole system into a couple of acoustic sub-elements, while the 3D Helmholtz solver model can predict directly acoustic modes as well as basic properties of combustion instability. Prediction results of both 1D and 3D models generally showed a good agreement with the measurements, even if there was a slight overestimation for instability range.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
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• pp.111-112
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• 2013

An experimental study of a dual swirl burner was conducted to analyze NOx emission in the lean conditions. The dual swirl burner is composed of a combination of swirling jet premixed(main section) and diffusion flames(pilot section). It was operated with a co-swirling configuration and overall equivalence ratios between 0.6 and 0.8. The purpose of this study is to analyze experimentally the characterization of flame temperature and NOx concentration in reacting zone and to supply the useful experimental data for numerical simulations. The measurements of temperature and NOx concentration were captured using a thin digitally-compensated thermocouple and a sampling quartz probe with quenching effect of sudden expansion, and were measured by the NOx analyzer of chemiluminescence method. We could analyse the NOx emission characteristics comparing the temperature distributions in the lean equivalence ratios.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.455-458
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• 2006

This study has numerically modelled the combustion processes of the turbulent swirling premixed lifted flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially- injected air jets induce the turbulent swirling flow which plays the crucial role to stabilize the turbulent lifted flame. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flame let model. Two-dimensional and three-dimensional computations are made for the various swirl numbers and nozzle length. In terms of the centerline velocity profiles and flame liftoff heights, numerical results are compared with experimental data The three-dimensional approach yields the much better conformity with agreements with measurements without any analytic assumptions on the inlet swirl profiles, compared to the two-dimensional approach. Numerical clearly results indicate that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling stoichiometric and lean-premixed lifted flames in the low-swirl burner.

• 대한기계학회논문집B
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• 제37권1호
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• pp.51-57
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• 2013

본 연구에서는 가스터빈 연소기에 적용하기 위한 예혼합 스월버너의 배기가스 및 화염안정성 최적화를 위하여 버너의 구조변경에 따른 연소특성을 실험적으로 분석하였다. 버너의 연료분사구조에 따른 배기가스 배출 특성을 파악하고자 단일연료분사구조와 이중연료분사구조를 갖는 예혼합 버너의 연소특성을 비교 분석하였으며 이중연료분사구조 적용 시 연료/공기 혼합특성이 향상되어 CO와 NOx의 배출농도가 감소하는 경향을 나타내었다. 또한, 노즐출구와 라이너의 지름 비(confined ratio)에 따른 연소부하 및 배기가스 특성을 분석한 결과 confined ratio 감소 시 연소부하 감소로 인해 NOx 배출농도가 감소되었으며, 체류시간의 증가로 인해 CO의 산화 반응이 증가하여 CO 배출농도가 감소하였다. 노즐분출속도는 30 m/s에서 배기가스특성이 우수하며, 속도 증가(40 m/s) 시 배가스특성이 저하되고 속도 감소(20 m/s) 시 화염안정성이 저하되었다.

• 한국자동차공학회논문집
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• 제12권2호
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• pp.83-90
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• 2004

A flywheel-driven rapid compression and expansion machine is developed and utilized for experimental study of homogeneous charge compression ignition combustion. Compression ignition of homogeneous charge in IC engines offers possibilities of realizing ultra-lean engine operation with greatly reduced NOx and particulate formation. Fundamental investigations are carried out in order to better understand this ideal engine combustion mechanism. Perfectly premixed propane-air mixtures of various equivalence ratio are compression-ignited in the rapid compression and expansion machine, and the characteristics of the auto-ignition and the following combustion process are analyzed.

• 대한기계학회논문집B
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• 제31권2호
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• pp.202-207
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• 2007

In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.