• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.175-178
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• 2014

The flame cell dynamics in 2-D opposed nonpremixed tubular configuration was investigated using high-fidelity numerical simulations. The diffusive-thermal instability occurs as the $Damk{\ddot{o}}hler$ number, Da, approaches the 1-D extinction limit of the tubular flames and several flame cells are generated depending on Da, and flame radius. In general, the number of flame cells are found close to the largest wave number from the linear stability analysis. It was also found from the displacement speed analysis that during the local flame extinction and cell formation, negative edge flame speed is observed due to small gain from reaction compared to large loss from diffusion.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.57-64
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• 1999

Initial flame development and propagation were visualized under the new ignition system developed to estimate the effects of ignition characteristics on the engine performance in a port injection SI engine. Effects of intake air flow characteristics were also investigated by three different kinds of the swirl control valve. Experiments were performed in an optical single cylinder engine modified form a commercial engine. Flame images were captured through the quartz window mounted in the piston by the high speed video camera and analyzed to compare initial flame development. Results show that IMEP tends to rise slightly as the ignition duration gets longer. The direction of flame propagation is decisively governed by the in-cylinder flow motion. Every flame grows toward the exhaust valve forming a kind of turbulent flame. Initial flame propaagation characteristics are very similar to ones analyzed form pressure data.

• Journal of Mechanical Science and Technology
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• v.14 no.8
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• pp.891-899
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• 2000

The flame speed may be decomposed into the burning speed and the flame transport speed. The flame transport speed is affected considerably by the flow direction, variation rate of flow direction, and flow speed in the combustion chamber. Especially, the flow direction and the variation rate of flow direction at the spark plug location during the ignition period have an important effect on the ignition process and the early flame propagation process. We measured the flow direction component and the variation rate of flow direction with a hot wire probe at the spark plug location. It was shown that the representative flow direction of ignition period is the right-vertical direction of crank shaft and it was used to investigate the variation rate of flow direction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.979-987
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• 2005

Numerical simulations were performed at atmospheric pressure in order to understand the effect of additives on flame speed, flame temperature, radical concentrations, $NO_x$ formation, and heat flux in freely propagating $CH_4-Air$ flames. The additives were both carbon dioxide and hydrogen chloride which had a combination of physical and chemical behavior on hydrocarbon flame. In the flame established with the same mole of methane and additive, hydrogen chloride significantly contributed toward the reduction of flame speed, flame temperature, $NO_x$ formation and heat flux by the chemical effect, whereas carbon dioxide mainly did so by the physical effect. The impact of hydrogen chloride on the decrease of the radical concentration was about $1.4\~3.0$ times as large as that of carbon dioxide. Hydrogen chloride had higher effect on the reduction of $EI_{NO}$ than carbon dioxide because of the chemical effect of hydrogen chloride. The reaction, $OH+HCl{\rightarrow}Cl+H_2O$, played an important role in the heat flux from flames added by hydrogen chloride instead of the reaction, $OH+H_2{\rightarrow}H+H_2O$ which was an important reaction in hydrocarbon flames.

• Journal of the Korean Society of Safety
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• v.23 no.2
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• pp.81-86
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• 2008

Experimental studies have been performed to examine the influences of wall obstructions in a rectangular confinement. Three wall obstacles with blockage ratios ranging from 10 to 30% were used. Temporally resolved flame front images were recorded by a high-speed video camera to investigate the interaction between a propagating flame and the obstacle. The local flame displacement speed and its probability density functions(PDFs) were obtained for the wall obstructions. During the interaction with the sharp-edges of the wall obstacles, the local propagation speed increased. The increase of local speed became larger as the obstruction ratio increased. However, the averaged flame displacement speeds with different blockage ratios were not significantly different within the chamber as shown in the paper of Park et al. The flame front interaction investigated in this work was less dependent of the obstacle obstructions compared to that published in the literature for large L/D.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.4
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• pp.50-60
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• 1992

Flame characteristics of periodic fuel jets were studied experimentally by supplying the fuel periodically using solenoid valve. Flame was observed using a high speed camera, a 35 mm camera and a cathetometer. Hot-wire ananometer was used to meature the speed of fuel flow at the nozzle exit to analyze the flow characteristics. Various types of flame characteristics such as the flame lift-off and extinction were observed for different ranges of period, duty, and flow rate, but the flame shape was not affected much by the variation in the flow rate. Decreasing duty of the pulses applied to the solenoid valve promotes lift-off and enhances premixed flame characteristics.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1240-1247
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• 2006

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by using G-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgrid G-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic sub grid G-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.244-254
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• 1996

Flow velocity was measured by, use of hot wire anemometer. Turbulence intensity was in proportion to mean flow velocity regardless of swirl velocity. And integral length scale has proportional relation with swirl velocity regardless of measurement position. Turbulent burning speed during flame propagation which was determined by flame photograph and gas pressure of combustion chamber was increased with the lapse of time from spark and was decreased a little at later combustion period. Because of combustion promotion effect, turbulent burning speed was increased according to increase of turbulence intensity. Burning speed ratio i.e. ratio of turbulent burning speed ($S_BT$) to laminar burning speed ($S_BL$) was found out by use of turbulence intensity u' and integral length scale $l_x$ , $\delta_L$ is width of preheat zone in laminar flame.

• Journal of the Korean Society of Combustion
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• v.13 no.3
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• pp.9-16
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• 2008

In this study, a cylindrical constant volume combustion chamber is used to investigate the flow and combustion characteristics of methane-air homogeneous mixture under various initial charge pressure, excess air ratios and ignition times. The flame and burning speed, mean gas speed are calculated by numerical analysis to analyze the combustion characteristics. It is found that the mean gas velocity during combustion has the maximum value around 300 ms and then decreased gradually on the condition of 10000 ms, and that the combustion duration is shorten and flame speed and burning velocity have the highest value under the conditions of an excess air ratio 1.1, an initial charge pressure of 0.2 MPa and an ignition time of 300 ms in the present study. And, the initial pressure and burning speed are in inverse proportion, so that it is in agreement with Strehlow who presented that the initial pressure and burning speed are in inverse proportion when the burning speed is under 50cm/s.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.117-119
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• 2015

This paper presents the methods and examples of proper orthogonal decomposition analysis for the understanding of high speed flame movements induced by combustion instabilities in a gas turbine. Phase resolved high-speed flame images were obtained from the combustion test of an industrial gas turbine at the rate of 2000 frame per second, and were utilized for the proper orthogonal decomposition. This analyzing method provided useful information regarding combustion instability characteristics bringing alleviation idea of the instabilities, such as principle modes of flame movement and their energy fractions which mean by which modes and how much the flame coherent structures are composed.