• Explosives and Blasting
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• v.18 no.1
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• pp.53-58
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• 2000

Thermal analysis, analysis of combustion residue and combustion characteristics measure ment such as burning rate or temperature were carried out to clarify the combustion mechanism of a tungsten- potassium perchlorate-barium chromate chromate delay powder. The results obtained are as follows. The main reaction of the delay powder of tungsten-potassium perchlorate-barium chromate is the oxidation of tungsten by potassium perchlorate. Barium chromate acts as a burning rate modifier, and the smaller the larger is the burning rate. Three types of delay composition used in this study show characteristic burning behavior. A stoichiomertric or a oxidizer-rich composition has a small linear burning rate. although it is has a large heat of combustion. On the other hand, a tungsten-excess or a fuel-rich composition with a small heat of combustion has a larger linear burning rate than the former, showing a small fractional oxidation of tungeten (below 10%) contained in the delay powder. From these results, a surface combustion mechanism is proposed for the combustion mechanism of this delay powder.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.109-112
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• 2015

This article describes a cellular instability and laminar burning velocity of simulated synthetic natural gas(SNG) including 3% hydrogen. In this study, experimental apparatus is employed using cylindrical bomb combustor, and investigation is carried out with high speed camera and Schlieren system. The cellular instability is caused by the buoyancy, hydrodynamic instability. Unstretched burning velocity can be determined by extrapolated stretch rate of zero point from measured results. These results were also compared with numerical calculation by Chemkin package with GRI 3.0, USC-II, WANG, C3 Fuel mechanism. As an experimental conditions, equivalence ratios was adjusted from 0.8 to 1.3. From results of this work, the one was found that the cellular instability has occurred by effect of thermal expansion rate and flame thickness. As the other results, unstretched laminar burning velocity was best coincided with GRI 3.0 mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.207-214
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• 2004

The burning velocities of conventional and oxygen-enriched methane flame in various equivalence ratio were determined by experiments. The validity of existing reaction mechanisms was examined in oxygen-enriched flame on the basis of the experiment results. Modified reaction mechanism is suggested, which was able to predict burning velocity of oxygen enriched flame as well as methane-air flame. Complementary study on reaction mechanisms shows the following results : Present experiment data were found to be more reliable in comparison with existing ones in a oxygen-enrichment condition. It was found that some modification in existing reaction mechanisms is necessary, since discrepancy between measurements and predictions is increasing with oxygen enrichment ratio. The sensitivity analysis was performed to discriminate the dominantly affecting reactions on the burning velocity in various oxygen enrichment and equivalence ratio. A modified GRI 3.0 reaction mechanism based on our experiment results was suggested, in which reaction rate coefficients of (R38) H+O$_2$<=>O+OH in GRI 3.0 reaction mechanisms were corrected based on sensitivity analysis results. This mechanism showed a good agreement in predicting the burning velocity and number density of NO in oxygen-enriched flame and would provide proper reaction information of oxygen-enriched flame at this stage.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.241-245
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• 2016

The purpose of this study was to investigate the bloating mechanism of artificial lightweight aggregates with different sizes (ESA, effective surface area). Aggregates were produced using hard clay, stone sludge, and a bloating agent in order to observe the effect of the gradation of the artificial lightweight aggregates. Kerosene and amorphous carbon were used as bloating agent. The particle size of the produced aggregate ranged from 3 mm to 9 mm. With regard to the amount of bloating agent to be used, 2 ~ 6 parts by weight were used. The specific gravity, absorption rate, and the type of aggregates produced by rapid sintering at $1075{\sim}1200^{\circ}C$ were determined. Microstructures were observed. When ESA had a value of 1 or below, kerosene, which has a high burning rate, was found to be advantageous for use as a bloating agent. When ESA had a value of 1 or above, carbon, which has a relatively low burning rate was found to be an advantageous bloating agent. It is thought that kerosene is more advantageous, as ESA decreases, for the production of aggregates having low water absorption rate.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.473-481
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• 2001

By depicting the transfer of heat and combustion reaction to take place within thin gas layers close to the propellant surface burning in a steady-state fashion, a mathematical equation has been deduced to describe the burning rate of solid propellant as a function of initial grain temperature and chamber pressure. It has been also assumed that chemical reaction could take place in premixing-diffusing zone but were carried out mainly in the reaction-flame zone. All these phenomena taken place in each zone of combustion have been assumed to be steady-state. In the present investigation, the equation, γ=$\kappa$$.$(1/R(T(sub)i+C))(sup)n$.$exp(-E(sub)a/R(T(sub)i+C))(P/z) is being presented and it is compared with experimental data. The proposed model has been tested and evaluated vis-a-vis strand burner data for three different propellants based on CTPB, and it has been found that the deviation of the computed burning rates from the measured rates ranged up to 2%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1465-1472
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• 2009

The effect of heat loss rate on NOx formation of $CH_4/air$premixed flame were examined numerically in a perfectly stirred reactor. The following conclusions were drawn. Under the adiabatic wall condition, an increase in the residence time causes a remarkable increases in NOx emission. Under the heat loss conditions, however, NOx decreases significantly as the heat transfer coefficient and residence time increase. As the heat loss rate increases, Thermal NO mechanism and Re-burning NO mechanism play an important role in the NOx reduction, but Prompt NO mechanism and $N_2O$-intermediate NO mechanism lead to the increase in NOx production. Although the NOx formation is actually related to complex NOx mechanism with the changes in the heat transfer coefficient and residence time, it was found that NOx concentration can be represented by independent Thermal NO mechanism. From these results, new NOx correlation combined with the heat loss rate and residence time was suggested for predicting the NOx concentration in a practical $CH_4/air$premixed combustor.

• Journal of Oral Medicine and Pain
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• v.26 no.2
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• pp.161-171
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• 2001

In order to determine how oral mucosal change relates to inducing factors of burning mouth syndrome, the difference in pain perception scale and keratinization rate between burning mouth syndrome patients and normal subjects were investigated. Twenty patients (13 female, 7 male, mean age: 59 years), presenting in the Department of Oral Medicine, Chonnam National University Hospital were participated in this study. All subjects had been complaining of constant oral burning pain for more than a year, none took any strong analgesics, and none had oral mucosal lesions. Twenty volunteers (11 females, 9 males, mean age: 25 years) were also participated in this study as a control group. The control subjects had never had any symptoms of oral burning pain. A thermal stimulation using a Nd-YAG laser and cytological smear were carried out to anterodorsal part of tongue, tip of tongue, the left buccal mucosa, the lower lip mucosa and the chief complaint site. Stimulation of the dorsum of left hand was also carried out to contrast the mucosal area of burning mouth syndrome subjects and the control subjects. The laser output power could be adjusted from 0.75W to 4W. The pain perception scale of the burning mouth syndrome subjects were lower than in control subjects in the chief complaint area, the anterodorsal part of tongue and the buccal mucosa(p<0.01). The keratinization rate of burning mouth syndrome subjects, however, was higher keratinization rate than in normal subjects in the same area and lower lip mucosa(p<0.001). From above results, the anterodorsal part of tongue is the most appropriate site to use diagnostic laser stimulation. The higher level of keratinization and the lower level of thermal pain perception of the burning mouth syndrome subjects are explained as a protective mechanism against xerostomia and burning sensations. The application of Nd-YAG laser stimuli and cytological smear to oral mucosal surface could therefore be usefully employed as appropriate and standardized diagnostic tools for chronic orofacial pain subjects.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.1
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• pp.89-96
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• 2016

The mechanism for laminar dust flame propagation can only be elucidated from a comprehensive mathematical model which incorporates conduction and radiation, as well as the chemical kinetics of particle devolatilization and gas phase and char reaction. The mathematical model for a flat, laminar, premixed coal-air flame is applied to the atmospheric coal-air mixtures studied by Smoot and co-workers, and comparisons are made with their measurements and predictions. Here the principal parameter for comparison is the laminar burning velocity. The studies of Smoot and co-workers are first reviewed and compared with those predicted by the present model. The effects of inlet temperature and devolatilization rate constants on the burning velocities are studied with the present model, and compared with their measurements and predictions. Their measured burning velocities are approximately predicted with the present model at relatively high coal concentrations, with a somewhat increased inlet temperature. From the comparisons, their model might over-estimate particle temperature and rates of devolatilization. This would enable coal-air mixtures to be burned without any form of preheat and would tend to increase their computed values of burning velocity.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.510-521
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• 2001

A nonlinear acoustic instability of subcritical liquid-oxygen droplet flames burning in gaseous hydrogen environment are investigated numerically. Emphases are focused on the effects of finite-rate kinetics by employing a detailed hydrogen-oxygen chemistry and of the phase change of liquid oxygen. Results show that if nonlinear harmonic pressure oscillations are imposed, larger flame responses occur during the period that the pressure passes its temporal minimum, at which point flames are closer to extinction condition. Consequently, the flame response function, normalized during one cycle of pressure oscillation, increases nonlinearly with the amplitude of pressure perturbation. This nonlinear response behavior can be explained as a possible mechanism to produce the threshold phenomena for acoustic instability, often observed during rocket-engine tests.

• Journal of the Korean Society of Combustion
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• v.5 no.2
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• pp.19-27
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• 2000

A turbulent combustion model, based on edge flame dynamics, is discussed in order to predict global extinction of turbulent flames. The model is applicable to the broken flamelet regime of turbulent combustion, in which global extinction of turbulent flame is achieved by gradual expansion of flame holes. The edge flame dynamics is the key mechanism to describe the flame hole expansion or contraction. For flames with Lewis numbers near unity, there is a $Damk{\ddot{o}}hler$ number, namely the crossover $Damk{\ddot{o}}hler$ number, at which edge flame changes its direction of propagation. The parametric region between the quasi-steady extinction condition and the edge-flame crossover condition is a metastable region, in that flames without edge can stay in their burning states while flames with edge have to retract to expand quenching holes. Using the above properties of edge flame, Hartley and Dold proposed a Lagrangian hole dynamics, which allows us to simulate transient variation of quenching holes. In their model, each stoichiometric surface is subjected to a random sequence of scalar dissipation rate compatible to the equilibrium turbulence. Then, each stoichiometric surface will evolve, according to the combustion map, dependent on the scalar dissipation rate and existence of flame edge, If all the burning surfaces are annihilated, the event can be declared as a global extinction. The consequence obtained from the above model also can be used as a subgrid model to determine local extinction occurring in a calculation grid.