• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.585-592
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• 2016

Visualization was done by using $CH^*$ chemiluminescence images and PMT measurements in order to understand the origin of fluctuating pressure and chemical luminosity at about 500 Hz frequency even in stable combustion, which was observed in recent experimental tests, and to find the physical correlation leading to Low Frequency Instability(LFI) in terms of phase angle. In stable combustion, chemical reactions are distributed along the shear layer flow showing a negative coupling(about 180 degree in phase angle) with combustion pressure. However, phase difference is shifted to a positive coupling showing less than 90 degree in unstable case. Also a periodic change in the distribution of chemical reactions is observed along with local flame extinction and the appearance of big scale vortex flow. In the transition to LFI, local flame extinction and small vortex flow start to appear in a row. As seen in the bluff body wake in reactive flow, the periodic appearance of vortex flow seems to share the same physical process of BVK(Bernard Von Karman) instability generation. Thus, the appearance of local extinction in 500 Hz fluctuations is gradually amplified to complete extinctions of about 20 Hz, and it leads into LFI.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.83-85
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• 2012

Experimental study in coflow jet flames has been conducted to investigate the effects of adding $N_2$, $CO_2$ and He to coflowing air-side in self-excitations. Differences in the behaviors between buoyancy-driven and diffusive-thermal self-excitations with similar frequency range are explored and discussed in laminar coflow jet flames.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.204-215
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• 2011

Flame stability is the one of the main mechanism of laminar lifted flame and flame propagation velocity becomes a yardstick to measure the flame stability. Bilge has presented the flame propagation velocity of the triple flame and the flame stability mechanism related the flame configuration and mixture fraction. However, there was not able to observe all process of flame ignition and extinction for small nozzle diameter. In this paper, we have subdivided the flame configuration and stability mechanism and classified the flame behavior with a nozzle diameter. Also we have subdivided the 'triple flame propagation opened' and the 'triple flame propagation closed' from the triple flame propagation of triple flame criterion.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.171-178
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• 2006

The performance in the practical combustion system including reciprocating engines and gas turbine combustors is being much governed by turbulent reacting flow that is often analyzed by both a laminar flamelets concept and flame interaction. The characteristics of laminar flame interaction have been investigated numerically to provide basic understanding of wrinkled turbulent flames under concentration interaction resulting from inhomogeneity in fuel-air mixing, especially focused on the transition of flame characteristics such as diffusion flame, partially premixed diffusion flame, and triple-layer flame by the variation in the degree of premixedness. The extinction stretch rates to the premixedness have also been obtained in this paper. The boundary defining the regime of the existence of triple-layer flames as functions of both stretch rate and premixedness has been determined which agrees well with previously reported experiment measuring OH radical concentration peaks based on PLIF.

• Journal of the Korean Society of Combustion
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• v.7 no.3
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• pp.9-15
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• 2002

Soot generation by combustion process has been investigated with objective of understanding of chemical reaction responsible for its formation in a coaxial laminar propane jet diffusion flame. For the direct photos, as the coflowing air flow rate is reduced, the area of soot luminous zone increases at first, then becomes smaller and smaller, and even disappears. The aspects of soot deposition can be acquired by using nine $15{\mu}m$ thin SiC fibers are positioned horizontally across the flame. Deposited soots on SiC fibers show the soot inception point and growth and soot oxidation zone in a typical propane diffusion. Soot is not generated anymore in a oxidizer deficient conditions of near-extinction and flame is fully occupied by transparent blue flame. It suggests that nonsooting pyroligneous blue reaction is being dominant in a oxidizer deficient ambience. In comparison with luminosities of SiC fibers and flame itself, indirect evidence is found that the process of soot nucleation and growth is endothermic reaction. It is remarkable that there exists two adjacent regions to have antithesis characteristics; one is exothermic reaction of blue flame and another endothermic reaction zone of soot formation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.1
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• pp.36-43
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• 1988

Boilers and diesel engines have many problems because their exhaust particles, i.e., soot have lots of bad influence on environment. And it's spray and flame have fundamentally axial symmetric shape. To investigate the relationship between fuel concentration distribution of spray and soot concentration distribution as well as temperature distribution of flame, we made a axial symmetric two phase spray-flame and analyzed the structure of is. The measuring method is the principle of the light extinction method for the spray-flame and onion peeling model is applied to analyze the radial distribution of fuel and soot concentration. The temperature of flame is measured by ø 0.4mm Pt-Pt.RH 3% thermocouple. The oils for the experiments are diesel oil and 10% water emulsified diesel oil. It was found that the soot concentration becomes higher as it comes near to the center of flame, and the fuel concentration does, too. And the soot concentration level of diesel oil is generally higher than that of the 10% water emulsified fuel. The maximum flame temperature of diesel oil is 1,17$0^{\circ}C$, however, 10% water emulsified diesel oil is 1,27$0^{\circ}C$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.5
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• pp.152-159
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• 2010

A combustion flame under the overhead power lines may be caused by breakdown disturbances in power systems. In this study, experiments were conducted for the purpose of investigating the reduction in insulation strength caused by combustion flame and the shape changes of the flame, and flashover characteristics and extinction phenomena of the flame in the simulated conditions of overhead power lines were examined under the application of a.c. and d.c. high-voltages. As the results of the experimental investigation, it is demonstrated that flame can remarkably reduce breakdown voltages of the air-gap in shorter range of the gap distance. As the gap distance increases, flame was quenched, before the flashover, by corona wind generated from the needle electrodes.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.27-31
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• 2009

An experimental study on the unsteady effect of the extinction limit was performed in ethene jet diffusion flames. To impose the unsteadiness on jet flames, the amplitude and frequency of a co-flow velocity was varied, and the two inert gases, $N_2$ and $CO_2$, were used to dilute the oxidizer for extinguishing concentration. The experimental results shows that large amplitude of velocity induces a low extinguishing concentration, which implies that flow variation affects the blow out mechanism. Also, the flow oscillation effects under high frequency attenuates the flame extinction. These results means that flow unsteadiness extends the extinction limit and finally minimum extinction concentration by inert gases. When the Stoke's 2nd Problem is introduced to explain the flow unsteadiness on extinction concentration, the solution predicts the effect of amplitude and frequency of velocity well, and hence it is concluded the effect of low frequency velocity excitation was attributed only to flow effect.

• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.38-43
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• 2008

Significant portion of the fire accident is caused by some troubles in electric circuits. To prevent the fire induced by those electric trouble, some indications of electric fire need to be suitably detected at the first stage of the fire development. With this background, the characteristics of soot yielding of electric cables have been investigated using a light extinction method. In this study, a light scattering method was compared with the light extinction method. A slot-type premixed-flame combustor was traversed to bum three types of electric cables by compulsion, then the mass decrease rate and the soot densities were measured. According to the experimental results, the light scattering method is preferred to the light extinction method when the soot yield ratio is relatively small. Thus the former method is more suitable to detect the occurrence of an electric fire in a power distributer box.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.107-111
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• 2002

A near extinction nonpremixed counterflow flame of 19% methane diluted by 81% nitrogen by volume and undiluted air at a low global strain rate, 20 s-1, was computed. Investigations were focused on effects of the duct thickness and velocity boundary conditions on the flame structure in normal and zero gravity conditions. The results showed that, under normal gravity conditions, the effects of the duct thickness and velocity boundary conditions were significant by shifting the flame position, but negligible in zero gravity. The differences in flame structure were caused by buoyancy, and hence should be considered in the measurements in normal gravity.