• 한국연소학회지
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• 제5권2호
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• pp.19-27
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• 2000

A turbulent combustion model, based on edge flame dynamics, is discussed in order to predict global extinction of turbulent flames. The model is applicable to the broken flamelet regime of turbulent combustion, in which global extinction of turbulent flame is achieved by gradual expansion of flame holes. The edge flame dynamics is the key mechanism to describe the flame hole expansion or contraction. For flames with Lewis numbers near unity, there is a $Damk{\ddot{o}}hler$ number, namely the crossover $Damk{\ddot{o}}hler$ number, at which edge flame changes its direction of propagation. The parametric region between the quasi-steady extinction condition and the edge-flame crossover condition is a metastable region, in that flames without edge can stay in their burning states while flames with edge have to retract to expand quenching holes. Using the above properties of edge flame, Hartley and Dold proposed a Lagrangian hole dynamics, which allows us to simulate transient variation of quenching holes. In their model, each stoichiometric surface is subjected to a random sequence of scalar dissipation rate compatible to the equilibrium turbulence. Then, each stoichiometric surface will evolve, according to the combustion map, dependent on the scalar dissipation rate and existence of flame edge, If all the burning surfaces are annihilated, the event can be declared as a global extinction. The consequence obtained from the above model also can be used as a subgrid model to determine local extinction occurring in a calculation grid.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.247-250
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• 2015

The characteristics of opposed nonpremixed tubular flames with radiation heat loss are investigated using linear stability analysis and 2-D numerical simulations. Two extinction limits, as the $Damk{\ddot{o}}hler$ number is small or large, are confirmed using finite difference method with a simple continuation method. It is verified that the results of linear stability analysis predict the number of flame cells and the critical Da starting cellular instability or amplification of temperature near both extinction limits with good resolution.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.46-49
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• 2006

Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction have been examined previously, with and emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.

• 한국연소학회지
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• 제9권4호
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• pp.35-46
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• 2004

Activation energy asymptotics (AEA) for Linan#s premixed-flame regime is revisited in this paper. First, the detailed AEA procedure for the premixed-flame regime is demonstrated, so that the practitioners of AEA could easily apply the method to their own problems. In addition, the controversies surrounding the premixed-flame regime, namely the closure controversy and fast-time instability paradox, are explained. Finally, the limitation of AEA, mainly arising from the wrong prediction of fuel leakage through the reaction zone, is examined and the Zel#dovich-Linan kinetics is introduced as an alternative to meet the needs of modern combustion analysis, where the detailed chemical structure of flame is demanded.

• 한국연소학회지
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• 제6권1호
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• pp.7-13
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• 2001

Propagation characteristics of tribrachial flames have been studied numerically in a two-dimensional fuel/oxidizer mixing layer. A flame is initiated by imposing a high temperature ignition source. Subsequent propagation of a tribrachial flame is traced. The flow redirection effect at the leading edge of a tribrachial flame increases the propagation speed beyond the corresponding stoichiometric laminar burning velocity. The effect of mixture fraction gradient on the propagation speed of a tribrachial flame is analyzed in a mixing layer considering that mixture fraction gradient increases as a tribrachial flame propagates toward upstream. As the flame curvature at the leading edge increases with decreasing mixture fraction gradient, the flow redirection effect becomes more pronounced on the flame propagation speed. As a result, the propagation speed of a tribrachial flame increases with decreasing mixture fraction gradient.

• 한국연소학회지
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• 제20권1호
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• pp.43-51
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• 2015

A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

• 한국추진공학회지
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• 제15권1호
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• pp.11-18
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• 2011

비슷한 형상을 가진 스위스롤 연소기의 물리적 크기에 대한 시험이 레이놀즈수와 담��러수의 독립적인 효과를 알아보기 위해 진행되었다. 이를 통해서 촉매연소와 비촉매연소의 소염한계 경계가 연소기의 크기 감소에 따라 다른 경향으로 좁아지는 것을 알 수 있었다. 추가적으로 연료의 화학적 성질의 중요성을 판단하기 위해 알칸기와 에테르기를 포함한 동종의 다른 형태 연료를 적용하여 시험을 수행하였다. 이러한 결과들을 통해 연소기의 크기와 연료의 형태에 따른 효과로 소형 연소기의 성능 및 그러한 장치들에 미치는 영향력에 대한 부분들이 논의되었다.

• 대한기계학회논문집B
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• 제36권8호
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• pp.857-864
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• 2012

복사열손실을 받는 확산화염의 선형 안정성 해석을 수행하여 복사강도와 Damkohler 수에 대한 화염 불안정이 나타나는 조건을 확인하였다. 대향류 유동장을 모델로 하여 Lewis 수는 1로 가정하였다. 반응속도 제한에 의한 소염근처에서 교란의 증가율은 실수의 고유값을 가지며 안정한계는 정상상태 소염조건과 정확하게 일치한다. 반면에 복사 열손실에 의한 소염 영역 근처에서 증가율의 고유값은 복소수이며 정상상태 소염 전에 맥동 불안정성이 예측된다. 진동하는 화염온도가 양의 실수 고유값을 갖는 정상상태 화염온도 보다 클 경우에만 한계 순환 안정 특성이 나타난다. 만약 그 온도보다 작게 되면 화염은 회복되지 못하고 소염된다. 넓은 복사강도 범위에 대하여 복사 열손실에 의한 불안정성의 안정한계 곡선을 도시하였다.