• 한국안전학회지
• /
• 제26권5호
• /
• pp.1-6
• /
• 2011

Flame extinction and the chemistry of stoichiometric methane/air mixture were investigated numerically in the PSR(perfectly stirred reactor). For the study, PSR code was modified to be possible to unsteady calculation, and the sinusoidal fluctuation was subjected to the residence time. In the region of residence time far from the extinction limit, combustion mode was strongly dependent on the frequency. The low frequency excitation provided the quasi-steady behavior on the temperature and the concentrations of related species, but small variation of temperature was observed under high frequency. In the region of residence time near the extinction limit, the mixture subjected above 1 KHz was still reacting even though extinction had to be occurred under quasi-steady concept. The attenuation of extinction limit resulted from that chemical time was comparable to the flow time. The mean mole fractions of both NO and CO were almost same regardless of imposed frequency. However, the average mole fraction of $C_2H_2$ was decreased as increasing frequency, which implies that soot yield might be reduced at the higher frequency of flow excitation. The result provides the basic concept for flame stabilization, and it will be used to design a mild combustor.

• 대한기계학회논문집B
• /
• 제28권12호
• /
• pp.1591-1599
• /
• 2004

A series of experiments were conducted to study the effectiveness of the extinction of a liquid pool fire with two different water atomizing nozzles. Fire source is a small-scale circular stainless steel pan of 120mm in diameter with the fuels of hexane and ethanol. K-type thermocouples were used to measure the flame and fuel temperature along the pool centerline and under fuel surface. A digital camera was used to visualize the process of the fire suppression. The experimental results show that water mist droplet size is l15∼180${\mu}{\textrm}{m}$ with nozzle A and 130∼190${\mu}{\textrm}{m}$ with nozzle B. The extinguishing time of pool fire was reduced with the increase of pressure. When water droplets are small, they do not reach the flame base since they may be deflected or evaporated by the fire plume. However, influence of flow rate is more important than droplet size on fire extinction. Among the fire extinction mechanisms, drop of flame temperature is superior to suffocation of $O_2$ concentration.

• 한국연소학회지
• /
• 제8권3호
• /
• pp.15-23
• /
• 2003

Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics in order to develop a prediction model for turbulent flame lift off. The essence of flame hole dynamics is derivation of the random walk mapping, from the flame-edge theory, which governs expansion or contraction of flame holes initially created by local quenching events. The numerical simulation for flame hole dynamics is carried out in two stages. First, a direct numerical simulation is performed for constant-density fuel-air channel mixing layer to obtain the turbulent flow and mixing fields, from which a time series of two dimensional scalar dissipation rate array is extracted at a fixed virtual flame surface horizontally extending from the end of split plate to the downstream. Then, the Lagrangian simulation of the flame hole random walk mapping projected to the scalar dissipation rate array yields temporally evolving turbulent extinction process and its statistics on partial quenching characteristics. The statistical results exhibit that the chance of partial quenching is strongly influenced by the crossover scalar dissipation rate while almost unaffected by the iteration number of the mapping that can be regarded as a flame-edge speed.

• 한국연소학회:학술대회논문집
• /
• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
• /
• pp.215-221
• /
• 2003

A series of experiments were conducted to study the effectiveness of the extinction of a liquid pool fire with two different water atomizing nozzles. Fire source is small-scale circular stainless steel pan of 120mm in diameter with the fuels of hexane and ethanol. K-type thermocouples were used to measure the flame and fuel temperature along the pool centerline and under fuel surface. A digital camera was used to visualize the process of the fire suppression. The experimental results show that water mist droplet size is $115{\sim}180{\mu}m$ with nozzle A and $130{\sim}190{\mu}m$ with nozzle B. The extinguishing time of pool fire was reduced with the increase of pressure. When water droplets are small, they do not reach the flame base since they may be deflected or evaporated by the fire plume. However, influence of flow rate is more important than droplet size on fire extinction. Among the fire extinction mechanisms, drop of flame temperature is superior to suffocation of O2 concentration.

• 한국분무공학회지
• /
• 제26권3호
• /
• pp.142-148
• /
• 2021

The objective of this study is to analyze the basic flame behavior characteristics using the single fuel droplet combustion of diesel, palm-based biodiesel, and canola-based biodiesel. The results were compared and analyzed through the post processed image, which was applied the threshold level for removing noise in the raw image. The raw image was taken by a high-speed camera during the entire combustion process. At the same time, the maximum flame length, which was measured by the application code of the MATLAB program, the ignition delay, and the combustion period were compared and analyzed.

• 대한기계학회논문집B
• /
• 제25권4호
• /
• pp.540-545
• /
• 2001

Many previous researches on the premixed flame in a tube have treated the unsteady flame behaviors in which the shape, position and intensity of the flame varied, but more detail and fundamental research has been necessary. The flame stabilization condition in a tube, a unique steady state, and the unsteady behaviors, using the stabilization condition as an initial condition, were carried out in recent years. In this paper, propane-air premixed flame was stabilized in a tube and the flame behavior was observed when the mean velocity variation was imposed into the opposite direction of the initial mean velocity. The velocity variation is larger than the burning velocity and longer than the reaction time scale. During the period of the velocity variation flame is not extinguished. But after the period of the mean velocity variation the flame could be re-stabilized or be extinguished depending on the experimental conditions: equivalence ratio, period of velocity variation and magnitude of velocity variation. The extinction mechanisms were classified into the two cases, one is caused by the flame stretch in the shear layer near the wall, and the other is caused by the vortices and vortexes, which are generted by the acoustic waves.

• 한국화재소방학회논문지
• /
• 제24권6호
• /
• pp.170-175
• /
• 2010

동축류버너를 이용한 제트확산화염에서 이산화탄소의 첨가가 매연 생성에 미치는 영향을 조사하였다. R-타입 열전대를 이용하여 화염대 및 황염과 청염의 경계온도를 측정하였다. 광감쇄법을 이용하여 화염이 존재하는 국소부분에서의 상대적인 매연 농도(1-I/$I_0$)를 측정하였다. 광원으로는 파장이 632.8nm인 He-Ne 레이저가 사용되었고 디텍터를 이용하여 매연입자에 의해 산란과 흡수를 겪은 후의 감쇄된 신호를 직접 측정하였다. 또한, 매연 생성에 있어서의 열적 효과를 알아보기 위해 산화제의 유속을 변화시켜 유속에 의한 영항을 알아보았다. 실험 결과로써, 황염과 청염 각각의 온도는 이산화탄소의 첨가에 따라 점차 낮아졌지만 황염과 청염의 경계온도는 거의 일정하였다. 산화제 측에 이산화탄소를 첨가함에 따라 상대적인 매연 농도는 낮아졌고 이는 산화제의 유속을 증가시켰을 때의 효과와 유사했다. 이것은 화염온도의 저하와 매연입자의 체류시간 감소에 기인하는 것으로 생각된다. 또한 이산화탄소의 첨가가 화염의 불안정성을 야기하여 순수 에틸렌/공기 화염에 비해 화염의 길이가 다소 증가하는 것으로 나타났다.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
• /
• pp.19-24
• /
• 2007

The deposition behavior of soot particles in a diffusion flame along a solid wall was examined experimentally by getting rid of the effect of natural convection utilizing microgravity environment. The microgravity environment was realized by using a drop tower facility. The fuel for the flame was an ethylene ($C_2H_4$) and the surrounding oxygen concentration 35% with the surrounding air velocity of $V_a$=2.5, 5, and 10 cm/s. Laser extinction method was adopted to measure the soot volume fraction distribution between the flame and burner wall. The results show that observation of soot deposition in normal flame was difficult from buoyancy and the relative position of flame and solid surface changes with time. The soot particle distribution region moves closer to the surface of the wall as the surrounding air velocity is increased. And the experiments determined the trace of the maximum soot concentration line. It was found that the distance between soot line and flame line is around 5 mm. That is, the soot particle near the flame zone tends to move away from flame zone because of thermophoretic force and to concentrate at a certain narrow area inside of the flame, finally, to adhere the solid wall.

• 대한기계학회논문집
• /
• 제13권3호
• /
• pp.517-527
• /
• 1989

본 연구에서는 국내 난방용 주연료인 연탄의 연소특성의 규명을 위한 기본 모델로서 일차적으로 형상을 단순화한 중공 원통형 고체연료의 연소모델을 개발하여 고체연료의 열분해 및 열분해 가스의 연소현상을 이론적으로 고찰하여 고체연료의 연속특성을 규명한다.

• 대한기계학회논문집
• /
• 제14권5호
• /
• pp.1222-1233
• /
• 1990

본 연구에서는 급속압축장치에서 실현된 단발분무하염내의 매연을 레이저음영 사진법에 의하여 가시화하고, 화염내의 매연농도의 시간적, 공간적분포를 조사한다. 또 전보에서 측정된 비증발분무내의 당량비분포와 비교검토하여 디젤화염내의 매연 생 성기구를 고찰하고, 분위기조건에 따른 착화지연이 매연생성에 미치는 영향 및 매연생 성과 열발생율과의 관계를 밝힌다.