• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.26-31
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• 2006

Flickering behaviors of lean premixed flame of propane/air and methane/air flame anchored by a pilot flame in a tube were investigated. Unsteady behaviors of the flame were monitored by a high speed ICCD camera and the flickering frequency was defined as the number of flame curvatures passing a fixed spatial point in a second. Unlike previous studies in which flames are in open condition so that the flickering mechanism is an unstable interaction of hot buoyant products with the ambient air, flames in this study are surrounded by a tube which means they are not open to ambient air, so that there is no interaction between hot buoyant products and ambient air. Despite the fact, there exists flickering phenomena and the flickering frequency ranges from 10 Hz to 50 Hz which is wider compared to previous studies. We relate the flickering mechanism to flame-generated vorticity and analytic solution for locally approximated flow is used. As a result, the relationship between flickering wavelength and dimensionless vorticity is acquired and the cause of higher range of flickering frequency is explained.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.89-94
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• 2013

This paper presents color video flame detection algorithm based on wavelet transform to remove detection of flickering non-flame objects. Conventional flame detection algorithms consist of simple or mixed functions using colors, temporal and spatial characteristics. But those algorithms detect non-flame objects as flame regions sometimes. False alarm reasons are flame-like objects with regular flickering lights such as car signal lamps, alarm lights etc. The proposed algorithm is to reduce false detection which is occurred in periodic flickering lights. At first, It segments the candidate flame regions by using frame difference, flame colors. Then it distinguish flame regions and non flame regions including flickering car lights by analyzing wavelet coefficients. Computer simulation results showed that the proposed algorithm removes false detection due to the periodic flickering lamps by performing 97.9% of correct detection rate while false detection rate is 7.3%.

• Journal of the Korean Society of Combustion
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• v.10 no.2
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• pp.35-41
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• 2005

Behaviors of lean premixed flame of propane/air and methane/air flame anchored by a pilot flame in a tube were investigated experimentally varying the mean velocity from 10 to 140 cm/s and the equivalence ratio from 0.45 to 0.8. Behaviors of both flames are divided into five regions of stable, flash-back, tail-out, flickering and vibrating. General characteristics of each region and Le number effect are investigated. Two main instabilities, flickering and vibration, are both unstable but the instability mechanism, the frequency and the amplitude of pressure fluctuation are different. In the edge of the vibrating region, pressure fluctuation repeats generation and extinction. Repeated growth and decrease of the amplitude of pressure fluctuation are explained by Rayleigh#s index.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.42-48
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• 2004

Lean laminar premixed propane and methane flames which were anchored by a hydrogen-pilot flame in a tube were investigated experimentally. The flame shapes were observed by varying mean velocity from 10cm/s to 140cm/s and equivalence ratio from 0.45 to 0.8. In this study, behaviors of flames are divided into five regions such as tail-out, flash-back, flickering, stable and vibrating flames with respect to the mean velocity and the equivalence ratio. Although the flames are unstable in both the flickering and the vibrating region, they have different characteristics such as the frequency, sound generation and creation process of flame curvature. The flickering region exists near the flammability limit and the flame flickers in a frequency of about 10Hz. When flame front is bended, the propane flame front is straightened and the methane flame front is bended more by thermo-diffusive instability. In the vibrating region, the flame vibrates emitting audible sound in a frequency of about 100Hz. In the boundary of vibrating region, the vibration of flame changes between two modes such as single frequency vibration and dual frequency vibration. Increase and decrease of vibration in each mode are determined by thermo-acoustic instability.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.1-10
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• 2018

An experimental study was performed for the behavior of the burner flame which results from burning of the liquid hydrocarbon fuel atomized by an ultrasonic transducer. Configurations of the flame and combustion-field were caught by both high-speed camera and thermo-graphic camera, and those images were analyzed in detail through a image post-processing. As a result, the combustion-field grew and reaction-temperature rose due to the strengthening of combustion reaction with the increasing flow-rate of carrier-gas. In addition, a phenomenon of flame flickering was discussed through the comparative analysis of the variational behavior between the visible flame and IR (Infrared) flame-field. Also, the flickering frequency of the flame was confirmed through FFT (Fast Fourier Transform) analysis employing the flame area.

• Journal of the Korean Society of Safety
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• v.31 no.3
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• pp.22-27
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• 2016

The use of electromagnetic wave has been interested in various energy industry because it enhances a flame stability and provides higher safety environments. However it might increase the pollutant emissions such as NOx and soot, and have harmful influence on human and environments. Therefore, it is very important to understand interaction mechanism between flame and electromagnetic wave from environmental point of view. In this study, an experiment was performed with jet diffusion flames induced by electromagnetic wave. Microwave was used as representative electromagnetic wave and a flickering flame was introduced to simulate the more similar combustion condition to industry. The results show that the induced microwave enhances the flame stability and blowout limit. The unstable lifted flickering flames under low fuel/oxidizer velocity is changed to stable attached flames or lift-off flames when microwave applied to the flames, which results from the abundance of radical pool. However, NOx emission was increased monotonically with increasing the microwave power as microwave power increased up to 1.0 kW. The effects might be attributed to the heating of combustion field and thermal NOx mechanism will be prevailed. Soot particle was examined at the post flame region by TEM grid. The morphology of soot particle sampled in the microwave induced flames was similar to the incipient soot that is not agglomerated and contain a lots of liquid phase hydrocarbon such as PAH, which soot particle formed near reaction zone is oxidized on the extended yellow flame region and hence only unburned young particles are emitted on the post flame region.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.4
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• pp.479-485
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• 2011

A video flame detection method analyze the temporal and spatial characteristics of the regions which have the flame-like color and moving objects in the input video. The video flame detector should be able to reduce a false alarm rate without the degradation of flame detection capability. The conventional methods can reject the false alarm caused by the car lights and some electric lights. However they make the false alarm caused by the warning lights, neon sign, and some periodic flickering lights which have the flame-like color and temporal features. This paper propose the video flame detection method with periodicity analysis based false alarm rejection. The proposed method can detect the periodicity of the flickering electric lights and can reject the false alarm caused by the periodic electric lights. The computer simulation showed that the proposed method did not make the false alarm in the test video with the periodic electric lights. But the conventional methods made a false alarm in the same test video.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.3
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• pp.9-16
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• 2016

An experimental study was performed to investigate the combustion characteristics of the liquid hydrocarbon fuel atomized by an ultrasonic oscillator. Configuration of the flame was caught by the high-speed camera, and images were analyzed in detail through a post-processing. In addition, the fuel consumption was measured using the balance during the combustion reaction. As a result, the consumption of atomized fuel increased with the increasing flow-rate of carrier-gas, but any correlation between the air/fuel ratio and carrier-gas flow-rate was not found. The variation of flame area was dependent on the fuel consumption and input power of the ultrasonic oscillator. FFT (Fast Fourier Transform) analyses using the flame area were conducted in order to discuss flame flickering.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1193-1199
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• 2012

A cup burner experiment was performed to investigate the effect of the oxidizer velocity and concentration on flame instability near extinction. Heptane was used as a fuel and air diluted by nitrogen and carbon dioxide was used in the oxidizer stream. Two types of flame instabilities at the flame base and at axial downstream were observed near extinction. The instability at the flame base could be characterized by cell, swing, and rotation modes, and the cell mode changed to the rotation mode through the swing mode as the oxidizer velocity increased. To assess the parameters for the flame instability, the initial mixture strengths, Lewis number, and adiabatic flame temperature were investigated under each condition. The Lewis number might be the most important among them, but it is impossible to generalize because of the insufficient number of cases. Furthermore, the axial periodic flickering motion disappeared at low and high oxidizer velocities near extinction. This resulted from the fact that low oxidizer velocity induced evaporated fuel velocity below the critical velocity and high velocity made the reacting fuel velocity comparable.