• Journal of the korean Society of Automotive Engineers
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• v.11 no.4
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• pp.13-18
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• 1989

연소 효율, 배기 특성을 제어하기 위하여 연소 반응대의 상세한 구조를 이해해야 하며 이를 토대로 열역학적 모델을 만들 필요가 있다. 본 고에서는 이미 여러 연구자들에 의하여 제안된 예혼합 화염의 반응대 구조에 대한 열적 모델과 확산모델을 소개하고 각각에 대한 응용과 가능성에 대하여 저자의 의견을 제시하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.603-607
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• 2011

Structure of flashback and reignition occurring near flameholder was experimentally investigated in a model combustor with V-gutter flameholder. The combustor has a long duct shape with cross section of $40{\times}40mm$ and City Nature Gas(CNG) were used as fuel. Measurements of chemiluminescence with high speed camera was used for visualization of flame structure. In the lean case, flashback distance depend on equivalent ratio. New flame occurred at the front tip of flameholder when flashback. Flashback flame moved toward downstream direction of combustor because mixture flow velocity had increased, and then re-ignition was caused by entering flow into recirculation zone that is formed behind the flameholder.

• Fire Science and Engineering
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• v.23 no.5
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• pp.90-95
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• 2009

The wind is very important factor in forest fire spread. Flame spread has a change through wind pattern change in forest fire. In order to analyze the forest fire flame spread rate, change of flame tilt depending on wind may be considering first. This is be cause the flame spread rate varies by the flame tilt changed due to transfer of heat. Especially, as wind speed grow, flame gets closer to surface, heat transfer ratio increase, virgin fuel bed reaches ignition temperature more rapidly, and flame moves faster. This study deduces, through experiment and physical figure analysis, relations on the change behavior of flame tilt due to wind. The value of flame tilt angle calculated from the equation and the experiment value showed average error angle of $3.3^{\circ}$, which is relatively smaller than results of previous studies that used other coefficient. Froude number coefficient A can be calculated in the method provided in this research for estimation of flame tilt angle of virgin fuel bed with varying thermal properties. The research finding is expected to be applied to future studies on flame spread through numerical analysis of heat transfer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.63-73
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• 2021

This paper presents a algorithm for automatic target recognition robust to the influence of the flame in order to track the target by EOTS(Electro-Optical Targeting System) equipped on UAV(Unmanned Aerial Vehicle) when there is aerial target or marine target with flame at the same time. The proposed method converts infrared images of targets and flames into a gradient vector field, and applies each gradient magnitude to a polynomial curve fitting technique to extract polynomial coefficients, and learns them in a shallow neural network model to automatically recognize targets and flames. The performance of the proposed technique was confirmed by utilizing the various infrared image database of the target and flame. Using this algorithm, it can be applied to areas where collision avoidance, forest fire detection, automatic detection and recognition of targets in the air and sea during automatic flight of unmanned aircraft.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.1
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• pp.60-67
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• 2005

Mild combustion or Flameless oxidation(FLOX) have been considered as one of the most prospective clean-combustion technologies to meet both the targets of high process efficiency and low pollutant emissions. A mild combustor with high air preheating and strong internal exhaust gas recirculation is characterized by relatively low flame temperature, low NOx emissions, no visible flame and no sound. In this study, the Steady Flamelet Approach has been applied to numerically analyze the combustion processes and NOx formation in the mild combustor. The detailed discussion has been made f3r the basic characteristics of mild combustor, numerical results and limitation of the present combustion modeling.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.17-17
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• 1997

극초음속 여객기와 군사용 항공기에 대한 수요가 증가함에 따라서 새로운 개념의 다양한 추진기관이 연구가 진행되고 개발되어 왔다. 초음속 항공기의 속도 영역은 마하 10-20 정도가 되는데 이 속도 한계를 극복하기 위하여 초음속 연소 램제트 엔진(SCRamjet; Supersonic Combustion Ramjet)이 제안되었다. 스크램 제트를 개발하기 위해서는 연료와 산화제의 혼합 효율 문제, 화염의 안정화 문제, 벽면의 냉각에 관한 문제 등 몇 가지 기본적인 문제들을 해결해야 한다. Univ of Michigan에서 실험한 연소기를 모델로 본 연구에서는 연료와 공기의 혼합에 관한 수치 연구를 수행하였다. 다원 혼합기체에 관한 축대칭 Navier-Stokes 방정식을 지배 방정식을 이용하였고 비평형 화학반응식을 고려하였다. 공간 차분에는 유한 체적법을 이용하였다. 대류 플럭스 항은 Roe의 Upwind FDS 기법을 사용하여 차분하였고 점성항에는 중심 차분법을 이용하였다. 시간 적분법으로는 근사 자코비안과 LU분할 기법을 이용한 완전 내재적 방법이 쓰였다. 난류 모델로는 Mentor에 의해 제안된 2 방정식 k-$\varepsilon$/k-$\omega$ 혼합모델을 사용하였다. 유동장이 실험에서의 찍은 사진과 유사한 모습의 충격파 간섭을 수치 모사하였고 수소가 확산되는 모습과 함께 노즐 lip 주위의 재순환 영역에 대해서 살펴볼 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1661-1668
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• 1990

In a turbulent premixed flame stabilized by the streamline step, and dominated by a coherent eddy, a flame micro-structure was investigated with analyzing the signals of temperature, the ion current, and schieren phtographs simultaneously. Generally the contours of large scale coherent eddies of schlieren photographs was considered as the flame front, however, the main reaction can be occurred within the eddy as a structure of fine flamelets scale. The surrounding burned gas of flamelets could not propagate to a unburned mixture, obstructing flamelets from propagating to a unburned mixture. Consequently, it could restrain flashback. The main reaction region was found to be located at higher temperature of the burned gas rather than at maximum rms of fluctuating temperature. The peak probability of higher temperature was 6 times greater than that of lower temperature. As it was difficult to infer a flame structure from PDF distribution of the fluctuating temperature in form of bimodal shape, it should be taken into consideration with other informations related to the sensitive flame front, for instance, ion current.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1113-1120
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• 1988

This paper presents the results of an experimental investigation on one dimensional excess enthalpy flame formed in a porous block. The investigation is undertaken in order to further the physical understanding of internal heat recirculation from reaction zone to unburned mixture. Two porous blocks are placed at both sides of combustion block to control the temperature distribution in the combustion block by means of radiation heat transfer. Mean temperature measurement reveals the general nature of the reaction zone in the porous material. It is conformed that the temperature of reaction zone exceeds the adiabatic flame temperature and the flame is stabilized at the out range of flammibility limit derived by conventional burner.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.457-462
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• 2011

This paper presents a numerical investigation of deflagration to detonation transition (DDT) induced by shock wave and flame interaction in ethylene-air mixtures. Also shows the change of DDT triggering time by wall cooling effect. A model is consisted of the compressible reactive Navier-Stokes equations. And the effect of viscosity, thermal conduction, molecular diffusion, chemical reaction and wall effect are included. Using this model, the generation of hot spot by repeated shock and flame interaction, occurrence of detonation, and wall cooling effect of detonation confining boundaries are studied.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.315-324
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• 2012

This paper presents a numerical investigation of the deflagration-to-detonation transition (DDT) of flame acceleration by a shock wave filled with an ethylene/air mixture as the combustible gas, considering geometrical changes by using obstacles and bent tubes. The model used consists of the reactive compressible Navier-Stokes equations and the ghost fluid method (GFM) for complex boundary treatment. Simulations with a variety of bent tubes with obstacles show the generation of hot spots through flame and strong shock-wave interactions, and restrained or accelerated flame propagation due to geometrical effects. In addition, the simulation results show that the DDT occurs with a nearly constant chemical heat-release rate of 20 MJ/($g{\bullet}s$) in our numerical setup. Furthermore, the DDT triggering time can be delayed by the absence of unreacted material together with insufficient pressures and temperatures induced by different flame shapes, although hot spots are formed in the same positions.