• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.197-202
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• 2010

A combustion chamber with a branch tube was built to investigate the characteristics of a spontaneous oscillating laminar premixed Bunsen flame. The flame behavior was observed, and the relation between the flame surface area and heat release rate was inspected. The equivalence ratio and mean velocity were fixed at 1.1 and 1.75 m/s, respectively. The amplitude of the pressure fluctuation in the combustion chamber was changed and the flame behavior was affected when the length ratio between the branch tube and combustion chamber (L:R) was varied. The $OH^*$, $CH^*$, and flame chemiluminescence had similar behavior qualitatively. There was linearity between the flame surface area and heat release rate.

• Journal of the Korean Society of Combustion
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• v.13 no.2
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• pp.14-22
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• 2008

The CH* chemiluminescence of premixed flames and their dependency on fuel types has been experimentally investigated on laminar methane and propane premixed flames. The measured chemiluminescence intensities are observed linearly proportional to the fuel flow rate, which could be interpreted as the CH* chemiluminescence signal is linearly proportional to the heat release rate under fuel lean conditions. The effect of equivalence ratio could be expressed by an exponential function as ${I_{CH*}}^{\propto}\;a_1\;{\exp}(b_1{\Phi})$, where $a_1\;=\;0.00054$ and $b_1\;=\;4.60$ for methane and $a_1\;=\;0.0056$ and $b_1\;=\;5.02$ for propane. Oscillating flames showed the temporal fluctuation of chemiluminescence intensity: however, the time averaged values are virtually identical to those of quiescent flames under the same fuel flow rate and equivalence ratio conditions. This observation suggests that there is no significant flame stretch effect on chemiluminescence intensity, in average values.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.2 s.257
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• pp.202-207
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• 2007

In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.750-756
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• 2002

The effect of equivalence ratio and velocity on the stability of flame in dump combustor was studied in an atmospheric pressure, laboratory scathe dump combustor operating natural gas. Traditionally, peak-to-peak pressure, fluctuation of the heat release rate and Rayleigh index were used to find and control the combustion instability. Cross correlation coefficients, Ci,j which is defined as the normalized value of the integration of the product of two of the mixer pressure, dump plane pressure and heat release rate, are introduced to see whether the flame is stable or not. Ci,j shows more sensitive to combustion status than Rayleigh index in steadily burning flame. Also, the result indicates that the amplitude of Ci,j between heat release and mixer pressure goes up before the flame at the rich de-stabilizing equivalence ratio near $\psi$=0.85. t means Ci:j at this case has a potential to detect the de-stablizing moment in prior to becoming unstable in dump combustor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.218-225
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• 2008

When the heat release and acoustic pressure fluctuations are generated in the combustor by irregular combustion, these fluctuations affect the mass flow rate of the propellants injected through the injectors. Also, the variations of the mass flow rate by these fluctuations again bring about irregular combustion and furthermore that is related with combustion instability. Therefore, it is very important to identify the mass variation for the pressure fluctuation on the injector and to investigate its transfer function. So, we first have studied quantifying the variation of mass flow rate generated in simplex swirl injector by injection pressure fluctuation. To acquire the transient mass flow rate in orifice with time, we have tried to measure of the flow axial velocity and liquid film thickness in orifice. The axial velocity is acquired through theoretical approach after measuring the pressure in orifice and the flow area in the orifice is measured by electric conductance method. As results, mass flow rate calculated by axial velocity and liquid film thickness measuring in orifice accorded with mass flow rate acquired by direct measuring method in the small error range within 1 percents in steady state and within 6 percents as average mass flow rate in pulsated state. Hence this method can be used to measure the mass flow rate not only in steady state but also in unsteady state because the mass flow rate in the orifice can acquire with time and this method shows very high accuracy based on the experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.963-970
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• 2005

The combustion instability of turbulent flames is the most important problem of the gas turbine combustor. Thus improved understanding of mechanisms of combustion instability is necessary for the design and operation of gas turbine combustors. In this study, the cause of the combustion instability in a rearward-step dump combustor was investigated with respect to the fuel flow modulation; choked fuel flow, unchoked fuel flow and fully premixed mixture flow. We observed various types of combustion instabilities with respect to the change of equivalence ratio, fuel flow conditions and fuel injection location. Particularly in the unchoked fuel flow condition, it was found that the oscillation time of combustion instability is strongly related to the convection time of the fuel and that the pressure fluctuation in a lab-scale combustor is highly related to the vortex and the equivalence ratio fluctuations due to fuel flow modulation and unmixedness of the fuel and air.

• Journal of ILASS-Korea
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• v.25 no.3
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• pp.119-125
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• 2020

In this paper, we used Helmholtz solver based on 3D finite element method to quantitatively analyze the effects of change of gain, time delay and time delay spread, which are the main variables of flame transfer function, on combustion instability in gas turbine combustor. The effects of the variable of flame transfer function on the frequency and growth rate, which are the main results of combustion instability, were analyzed by applying the conventional heat release fluctuation model and modified one considering the time spread. The analysis results showed that the change of gain and time delay in the same resonance mode affected the frequency of the given resonance modes as well as growth rate of the feedback instability, however, the effect of time delay spread was not relatively remarkable, compared with the dominant effect of time delay.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1736-1743
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• 1992

The combustion in the cylinder of spark ignition engine is completed after the delayed time that the liquid film fuel is vapourized as flowing into the combustion chamber. It is necessary to enhance the homogeneity of mixture and the combustion phenomenon in order to improve the heat efficiency and the emission characteristics of spark ignition engine. The main purpose of this paper is to manufacture a combustion analyzing system and examine closely the influence of non-uniformity due to the liquid film fuel flowing in the intake manifold on the combustion characteristics by using a 4 stroke multi- cylinder spark ignition engine. Moreover, with each cylinder, the interpretation of combustion characteristics by indicator diagram and the concentration of exhaust gas were investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.2
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• pp.42-50
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• 1995

This paper proposes a new method to investigate combustion phenomena using the variation of crankshaft speed, From the idea that the variation of crankshaft speed contains the information of combustion, the energy method is applied as a single degree of freedom. Through the comparison of measured and calculated crankshaft speed, the proposed energy model is proved to be effective. When the crankshaft speed is used in the energy equation, filtering of the speed is required. The frequency components of cylinder pressure are analyzed and the coefficients of Fourier series above the twelfth frequency of engine speed are considered as a noise. As an example of application of this research, some combustion analyses like mean effective pressure, heat release rate, and misfire detection were carried out.

• Journal of the Korean Society of Safety
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• v.38 no.4
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• pp.39-46
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• 2023

Pine trees, which account for 23% of the forested area of the Republic of Korea, are highly vulnerable to fire in comparison to broad-leaved trees due to the presence of consistent water tube sections throughout the year and resin that is composed of approximately 20% oil. In addition, the pattern of forest fires is determined by weather, topographic conditions, and fluctuation in moisture content. Therefore, when fire breaks out in pine tree forests during the dry season (January to March), it is difficult to extinguish, and it quickly spreads. In this study, the combustion characteristics of pine needles, pine cones, and pine branches in the water tube sections of living pine trees were compared and analyzed in accordance with the moisture content as per the ISO 5660-1. The monthly moisture content was analyzed from January to March, and it was found to be the lowest in March, with 53.6% for pine needles, 51.9% for pine branches, and 10.9% for pine cones. In particular, pine cones were more vulnerable to fire as compared to pine needles and pine branches because their moisture content was more than five times lower than that of pine needles and branches. The ignition time, which affects the speed of flame propagation, was the most rapid in March, and the fastest ignition time was for pine cones, at 19 seconds, followed by 34 seconds for pine needles, and 256 seconds for pine branches. The pine branches were the last to be ignited due to the effect of density, according to the thickness and specific gravity of the specimen. The peak heat release rate, which is a measurable index of fire intensity, was analyzed for pine cones and found to be 184.28 kW/m² , while the mean effective heat of combustion was 19.79 MJ/kg, and the total heat release rate was 39.7 MJ/m² , and these values were higher than those of pine branches and pine needles. Thus, we determined that the flame propagation speed and fire intensity according to the moisture content can be used to evaluate the risk of fire to the water tube section of pine trees. It is suggested that because of the combustion characteristics of the pine cone in March, that is when the forest is most vulnerable to fires.