• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.565-572
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• 2004

Numerical stability analysis of one-dimensional axial flow in solid rocket motors is performed based on the Euler equation coupled with an unsteady combustion equation of solid propellant. In order to check the numerical scheme, behavior of a standing wave in a closed tube is examined. A standing wave in solid rocket motor decays or grows depending on the total effect of propellant combustion, nozzle flow, and so on. The stability boundary of the fundamental mode standing wave is determined by changing one of the combustion parameters. In addition growth rates of the wave are calculated numerically in relatively low Mach number flow region for the motors with different port and nozzle throat diameters. The results obtained here agree well with the approximate solution. The same scheme is applied to a motor with shorter length and L＊-instability is observed.

• Journal of the Korean Ceramic Society
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• v.33 no.4
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• pp.411-417
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• 1996

Ultrafine NiO/YSZ (Yttria Stabilized Zirconia) powders were made by using a glycine nitrate process which is used as anode material for solid oxide fuel cells. The specific surface areas of synthesized NiO/YSZ powders were examined with controlling pH of a precursor solution and the content of glycine. The binding of glycine with metal nitrates occurring in the precursor solution was analyzed by using FTIR. The characteristics of synthesized powders were examined with X-ray diffraction(XRD) Brunauer Emmett Teller with N2 absorption. scanning electron microscopy (SEM). and transmission electron microscopy (TEM). Ultrafine NiO/YSZ powders of 15-18 m2/g were obtained through GNP when the content of glycine was controlled to 1 or 2 times the stoichiometric ratio in the precursor solutions. Strongly acid precursor solution increased the specific surface area of the synthesized powders. This is suggested to be the increased binding of metal nitrates and glycine under a strong acid solution of pH=0.5 that lets glycine consist of mainly the amine group of {{{{ { NH}`_{3 } ^{+ } }}. After sintering and reducing treatment of NiO/YSZ powders synthesized by GNP the Ni/YSZ pellet showed ideal microstructure where very fine Ni particles of 3-5 ${\mu}{\textrm}{m}$ were distributed uniformly and fine pore around Ni metal particles was formed. leading to anincrease of the triple phase boundary among gas Ni and YSZ.

• Journal of the Korean Society of Combustion
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• v.10 no.3
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• pp.25-33
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• 2005

Fast-time instability is investigated for diffusion flames with Lewis numbers greater than unity by employing the numerical technique called the Evans function method. Since the time and length scales are those of the inner reactive-diffusive layer, the problem is equivalent to the instability problem for the $Li\tilde{n}\acute{a}n#s$ diffusion flame regime. The instability is primarily oscillatory, as seen from complex solution branches and can emerge prior to reaching the upper turning point of the S-curve, known as the $Li\tilde{n}\acute{a}n#s$ extinction condition. Depending on the Lewis number, the instability characteristics is found to be somewhat different. Below the critical Lewis number, $L_C$, the instability possesses primarily a pulsating nature in that the two real solution branches, existing for small wave numbers, merges at a finite wave number, at which a pair of complex conjugate solution branches bifurcate. For Lewis numbers greater than $L_C$, the solution branch for small reactant leakage is found to be purely complex with the maximum growth rate found at a finite wave number, thereby exhibiting a traveling nature. As the reactant leakage parameter is further increased, the instability characteristics turns into a pulsating type, similar to that for L < $L_C$.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.102-108
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• 2009

Fossil power plants firing lower grade coals or equipped with modified system for NOx controls are challenged with maintaining good combustion conditions while maximizing generation and minimizing emissions. In many cases significant derate, availability losses and increase in unburned carbon levels can be attributed to poor combustion conditions as a result of poorly controlled local fuel and air distribution within the boiler furnace. In order to develop a on-line combustion tuning system, field test was conducted at operating power boiler. During the field test the exhaust gases' $O_2$, NOx and CO was monitored by using a spatially distributed monitoring grid located in the boiler's high temperature vestibule and upper convective back-pass region. At these locations, the flue gas flow is still significantly stratified, and air in-leakage is minimal which enables tracing of poor combustion zones to specific burners and over-fire air ports. using these monitored information we can improving combustion at every point within the furnace, therefore the boiler can operate at reduced excess $O_2$ and gas temperature deviation, reduced furnace exit gas temperature levels while also reducing localized hot spots, corrosive gas conditions, slag or clinker formation and UBC. Benefits include improving efficiency, reducing NOx emissions, increasing output and maximizing availability. Discussion concerning the reduction of greenhouse gases is prevalent in the world. When taking a practical approach to addressing this problem, the best way and short-term solution to reduce greenhouse gases on coal-fired power plants is to improve efficiency. From this point of view the real time optimized combustion tuning approach is the most effective and implemented with minimal cost.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.45-52
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• 2009

Fossil power plants firing lower grade coals or equipped with modified system for $NO_x$ controls are challenged with maintaining good combustion conditions while maximizing generation and minimizing emissions. In many cases significant derate, availability losses and increase in unburned carbon levels can be attributed to poor combustion conditions as a result of poorly controlled local fuel and air distribution within the boiler furnace. In order to develop a on-line combustion tuning system, field test was conducted at operating power boiler. During the field test the exhaust gases' $O_2,\;NO_x$ and CO was monitored by using a spatially distributed monitoring grid located in the boiler's high temperature vestibule and upper convective rear pass region. At these locations, the flue gas flow is still significantly stratified, and air in-leakage is minimal which enables tracing of poor combustion zones to specific burners and over-fire air ports. using these monitored information we can improving combustion at every point within the furnace, therefore the boiler can operate at reduced excess $O_2$ and gas temperature deviation, reduced furnace exit gas temperature levels while also reducing localized hot spots, corrosive gas conditions, slag or clinker formation and UBC. Benefits include improving efficiency, reducing $NO_x$ emissions, increasing output and maximizing availability. Discussion concerning the reduction of greenhouse gases is prevalent in the world. When taking a practical approach to addressing this problem, the best way and short-term solution to reduce greenhouse gases on coal-fired power plants is to improve efficiency. From this point of view the real time optimized combustion tuning approach is the most effective and implemented with minimal cost.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.3
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• pp.205-212
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• 2002

The catalytic combustion of benzene, toluene and xylene over Pt-based catalyst was investigated in a fixed bed flow reactor system with atmospheric pressure to recycle the waste industrial catalyst for the processes of removing volatile organic compounds. According to the pretreatment condition, the properties of the waste Pt-based catalyst were characterized by XRD (X-ray diffraction) and BET (Brunauer-Emmett-Toller). In the carte of air pretreatment, 20$0^{\circ}C$ was found to be optimal, and increasing pretreatment temperature resulted in the reduction of the catalytic activity. When Pt-based catalyst pretreated at 20$0^{\circ}C$ by alto was retreated by hydrogen, the catalytic activity increased by increasing treatment temperature. In the case of HNO$_3$aqueous solution pretreatment, the catalytic activity decreased by increasing the concentration of HNO$_3$aqueous solution. The catalytic activity was seen to observe the following sequence : benzene > toluene > xylene.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.159-165
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• 2002

Numerical analysis of dynamic contact and stress developing in the high-speed driven valve of an internal combustion engine is presented. The valve is modeled by finite element techniques, and the dynamic contact between the valve and the valve seat is analyzed by the solution strategies of differential algebraic equations. Also an iterative scheme similar to the augmented Lagrange multiplier method is employed to enforce the contact constraints. It is shown that the contact and separation between the valve and the valve seat can be computed by the finite element techniques without assuming the artificial springs, and the efficiency and accuracy of the solution are demonstrated by the numerical examples.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.31-39
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• 2003

Numerical analysis for valve train dynamics of an internal combustion engine is presented. The components of the valve train are modeled by finite element techniques, and the dynamic contacts between the components are analyzed by the solution strategies of differential algebraic equations. Also an iterative scheme similar to the augmented Lagrange multiplier method is employed to enforce the contact constraints. It is shown that the contact and separation between the components of the valve train can be computed by the finite element techniques, and the numerical examples are presented to demonstrate the efficiency of the solution.

• Fire Science and Engineering
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• v.19 no.4 s.60
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• pp.26-31
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• 2005

In order to evaluate the fire and explosion involved and to ensure the safe and optimized operation of chemical processes, it is necessary to know combustion properties. Explosion limit is one of the major combustion properties used to determine the fire and explosion hazards of the flammable substances. In this study, the explosion limits of alcohols were predicted by using the normal boiling points and the flash points based on a solution theory. The values calculated by the proposed equations agreed with literature data within a few percent. From the given results, using the proposed methodology; it is Possible to Predict the explosion limits of the other flammable substances.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.991-995
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• 2021

In this paper, synthesize MoO₃ particles with various particle properties by control growth influence factors was mainly studied. The experimental conditions were established in molar ratio of Mo:urea and pH levels. The plate-type of MoO₃ particles were formed without proceeding any established conditions, but the rod-shape particles were formed by adjusting molar ratio of Mo:urea. Also, different ranges of the particle size were formed by adjusting experimental conditions. Through the results, it was confirmed that particles with a size in the range of 300 ~ 400 nm were obtained by adjusting precursor concentration and the micrometer size of particles were formed by increase pH levels. The properties of the particles formed accordingly by setting various factors that can affect the growth process of MoO₃ particle was analyzed as variables and the particle growth behavior was also observed.