• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.1-7
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• 2013

Flame stabilization characteristics of premixed flames in narrow annular coaxial tubes (NACT) were investigated experimentally. The NACT burner was proposed as a model of a cylindrical refractory burner, and it was made of quartz tubes. Flame stabilization conditions affected by the characteristic length of the burner was investigated with the variation of the equivalence ratio and the flow rates. Flame behaviors in narrow spaces could be directly observed. Conclusively, more wide flame stabilization conditions could be obtained at the case of the decreased channel scale. A flame instability, such as combustion noise was detected concerned with the flame oscillation observed at the surface of multi channel stage. Some flame propagation characteristics had complicated tendencies that may exist in practical porous-media combustors. Therefore, this NACT burner can be a basic configuration for the development of flame stabilization model in porous media combustor, and it will enhance our understanding about the behavior of flames in meso-scale combustion spaces.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.24-30
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• 2013

Flame stabilization characteristics of premixed flames in an annular coaxial 5-tubes burner (AC5TB) were investigated experimentally. The AC5TB was made of five quartz tubes, and the flame stabilization conditions in that burner were investigated with the variation of equivalence ratio and the flow velocities. Flame behaviors inside of narrow annular tubes could be observed directly. Overall flame stabilization conditions were similar to that of the previous study, while the flame behaviors and structures were different mainly due to the controlled uniform distribution of the velocities in channels. Flame flashback conditions were thought to be governed by the competition between heat release rate, heat loss and heat recirculation in each channel. Stationary flames at a fixed location were compared in its velocity distribution and burned gas temperature across the channel. This AC5TB can be a basic configuration for the development of flame stabilization model of porous media combustors, and it will help understand about the real behavior of flames in meso-scale combustion spaces.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.430-432
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• 2011

An experimental study of the flame response in a turbulent premixed combustor has been conducted in order to investigate mechanisms for combustion instabilities in lean premixed gas turbine combustor. A lab-scale combustor and mixing section system were fabricated to measure the flame transfer function. 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 and operating conditions.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.6
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• pp.442-448
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• 2009

To evaluate the combustion mechanism of each droplet cluster downstream of the premixed spray flame, the simultaneous time-series measurements were conducted by using optical measurement system consisting of laser tomography, multi-color integrated Cassegrain receiving optics (MICRO) and phase Doppler anemometer (PDA). Furthermore, the group combustion number of droplet cluster was estimated experimentally, and the combustion mechanism of droplet cluster was examined applying the theoretical analysis. The group combustion number, $G_c$, was experimentally estimated about all droplet cluster verified by planar images, and it was classified into the internal group combustion mode and the external group combustion mode according to the theoretical analysis. It is found that there are cases in which the group combustion number estimated experimentally for droplet cluster agree or disagree with the classification by theoretical analysis. The reason of disagreement is considered due to that the group combustion number was only estimated by the geometrical arrangement of droplets in cluster, and that the actual phenomenon is three-dimensional but the measurement system is two-dimensional.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.4-4
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• 1999

최근 충남대에서는 다양한 추진제와 연소 조건으로 액체로켓 연소 실험이 진행되고 있으며 그에 비례하여 많은 사고들이 발생하고 있다. 한 예로 GO$_2$/kerosene을 추진제로 하는 노즐삭마 시험용 로켓엔진(추력 1001bf, 연소실 압력 600psia) 개발 중에 화염이 인젝터면에 형성되어 인젝터면을 손상시키는 사고를 여러 번 경험하게 되었다. 본 연구는 인젝터 손상의 원인을 규명하여 안정적인 인젝터 설계에 도움을 주기 위한 목적으로 실험용 동축 인젝터를 제작하여 화염 부상 특성을 실험적으로 연구하였다. 사용된 인젝터는 연료인 Kerosene을 접선형 선회기로부터 90$^{\circ}$의 원뿔 각을 가지고 분무되도록 설계하였으며, 그 주위로 산하제인 GO$_2$가 연소실의 축방향에 수평하게 분무되도록 설계하였다. 2-유체 동축 인젝터의 난류 확산 화염에서 연료와 산화제의 혼합은 화염 특성을 결정하는 주요 변수이므로 인젝터로부터 분무되는 추진제간의 유량을 변화시켜 화염 부상 특성을 연구하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.46-53
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• 2017

This paper deals with an acoustic model for a lean premixed gas turbine combustor composed of three stages: premixing chamber, nozzle and flame tube. Our model is given as an acoustic transfer function whose input is a heat release rate perturbation and output is a velocity perturbation at a flame location. We have shown that the resonance frequencies are functions of three round-trip frequencies of acoustic wave in each stage, and area ratios between stages. By analyzing poles of the acoustic transfer function, we could characterize resonant frequencies and their dependency on various system parameters of a combustor. It was found that our analytic findings match with existing numerical and experimental results in literature.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.593-600
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• 1999

The structure of premixed turbulent flames in constant volume vessel was investigated by using a laser tomography. The flame structure was visualized by passing a laser sheet with 0.2mm thick and 2 cm wide through the turbulent flames to obtain their 2-D images. From the obtained images islands of reactants as well as of products were found at least in the 2-D images when the turbu-lence intensity was above 0.4m/s. Moreover in order to obtain the characteristic flamelet thickness the light intensities of them were digitized and processed into three colors incorporating two appro-priate threshold values in the image analysis. As the result the averaged value of charactertistic flamelet thickness was found to be about two times compared to laminar one.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.437-444
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• 2005

Experiments were carried out in an atmospheric pressure, lab-scale gas turbine combustor to see the effect of partial premixing on unstable flame structure and Nox emission characteristics. The swirl angle is 45 deg., fuel-air mixing degrees were varied 0, 50 and 100% respectively at equivalence ratio ranging from 0.53 to 0.79. The evolution of phased-locked OH chemiluminescence images were acquired with an ICCD. NOx emission characteristics were also investigated at each experimental condition. The effect of the fuel-air mixing degree on the flame structure was obtained from phase-locked $OH^*$ images. And it was obtained from local heat release characteristics that the information about the region which the combustion instability was amplified or damped. It also could be confirmed that $\sigma$ has greatly influence on NOx emission characteristics at lean regimes. It would be expected that it could provide invaluable data for understanding the mechanism of combustion instability.

• Journal of ILASS-Korea
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• v.3 no.4
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• pp.43-49
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• 1998

In order to clarify the effect of equivalence ratio and kinds of fule in flame structure, a numerical simulation of triple flame developed in a co-flowing methane-air and air stream was carried out by the elementary chemical reaction mechanism. The following conclusions were obtained. Equivalence ratio at which the apparent burning velocity is maximum is a little larger than that of the one-dimensional premixed flame. Apparent burning velocities are two times higher than that of the one-dimensional premixed flame for the methane-air. The flame thrusts out forward in the downstream of the boundary between mixture and air stream, and a part of the flow is bent and forks out in this protruding flame so that a triple flame is originated; this triple flame is composed of fuel rich and lean premixed flame branches and a diffusion flame branch. Near the equivalence ratio at which the burning velocity of rule-dimensional premixed flame is the largest the effect of one-dimensional premixed flame becomes large and the fuel rich premixed flame advances and becomes vertical to the flow direction.