• Journal of Korean Society for Atmospheric Environment
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• v.32 no.6
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• pp.593-602
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• 2016

The physicochemical characteristics of particulate matter emissions from various vehicle's fuel types were studied at the facility of Transport Pollution Research Center(TPRC), National Institute of Environmental Research (NIER), Korea. Three different types of fuels such as gasoline, liquefied petroleum gas (LPG) and diesel were tested on the NIER driving mode and the constant speed modes(30, 70, and 110 km/h). Chemical composition of submicron particles from vehicle emissions was measured by the High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during running cycles. Organics were dominant chemical species of particulate matter emissions for all three different vehicles' fuel types. Moreover, regardless of fuel types, emission rate of organics and inorganics decreased as the average speed of vehicle increased. The portion of fully oxidized fragment families of $C_xH_yO_z$ accounted for over 98% of organic aerosol(OA) in LPG and diesel vehicles, while the relatively high fraction of $C_xH_y$ in OA was observed in gasoline vehicle.

• Journal of Hydrogen and New Energy
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• v.24 no.3
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• pp.223-229
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• 2013

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a power generation system to convert chemical energy of fuels and oxidants to electricity directly by electrochemical reactions. As a catalyst support for PEMFCs, carbon black has been generally used due to its large surface area and high electrical conductivity. However, under certain circumstances (start up/shut down, fuel starvation, ice formation etc.), carbon supports are subjected to serve corrosion in the presence of water. Therefore, it would be desirable to switch carbon supports to corrosion-resistive support materials such as metal oxide. $TiO_2$ has been attractive as a support with its stability in fuel cell operation atmosphere, low cost, commercial availability, and the ease to control size and structure. However, low electrical conductivity of $TiO_2$ still inhibits its application to catalyst support for PEMFCs. In this paper, to explore feasibility of $TiO_2$ as a catalyst support for PEMFCs, $TiO_2$ nanofibers were synthesized by electrospinning and calcinated at 600, 700, 800 and $900^{\circ}C$. Effects of calcination temperature on crystal structure and electrical conductivity of electrospun $TiO_2$ nanofibers were examined. Electrical conductivity of $TiO_2$ nanofibers increased significantly with increasing calcination temperature from $600^{\circ}C$ to $700^{\circ}C$ and then increased gradually with increasing the calcination temperature from $700^{\circ}C$ to $900^{\circ}C$. It was revealed that the remarkable increase in electrical conductivity could be attributed to phase transition of $TiO_2$ nanofibers from anatase to rutile at the temperature range from $600^{\circ}C$ to $700^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.3
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• pp.309-319
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• 2011

We experimentally investigated lifted propane jet flames diluted with nitrogen to obtain flame-stability maps based on heat-loss-induced self-excitation. We found that heat-loss-induced self-excitations are caused by conductive heat loss from premixed flame branches to trailing diffusion flames as well as soot radiation. The conductive-heat-loss-induced self-excitation at frequencies less than 0.1 Hz is explained well by a suggested mechanism, whereas the oscillation of the soot region induces a self-excitation of lift-off height of the order of 0.1 Hz. The suggested mechanism is also verified from additive experiments in a room at constant temperature and humidity. The heat-loss-induced self-excitation is explained by the Strouhal numbers as a function of the relevant parameters.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.300-309
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• 2017

A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.

• Korean Journal of Microbiology
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• v.46 no.1
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• pp.68-72
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• 2010

The ${\beta}$-1,4-glucanase gene of Bacillus licheniformis B1 was expressed in Esherichia coli BL21, and a protein with a mass of 50 kDa that was soluble was overproduced. A protein with a mass of 37 kDa was secreted from B. licheniformis. It seems that the ${\beta}$-1,4-glucanase produced in E. coli contained the leader peptide and unprocessed carboxy-terminal region, but its processing occurred in the carboxyterminal in Bacillus. The optimal temperature of ${\beta}$-1,4-glucanase was $40^{\circ}C$. The enzyme still had 76% maximal activity at $60^{\circ}C$. The optimal pH of the enzyme was 7. The enzyme retained considerable activities over the weak-acidic, neutral, and weak-basic pH range. Acidic fungal cellulases are used in food, detergent, pulp, paper, textile industries. However, studies about neutral and alkaline cellulase are not enough. The cellulase developed in this study may be useful for industrial applications in the fields of biofuel development.

• Polymer(Korea)
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• v.34 no.2
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• pp.137-143
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• 2010

A series of partially fluorinated, sulfonated poly(biphenylene-co-sulfone)ether containing perfluorocyclobutane(PFCB) groups were prepared for fuel cell applications through three synthetic steps: synthesis of trifluorovinylether-terminated monomers, thermal cycloaddition and post-sulfonation. Two kinds of trifluorovinylether-terminated monomers were synthesized and statistically copolymerized via thermal cycloaddition to obtain a series of polymers containing 20-60 mol% of biphenyl units(PBS-X). The post-sulfonation of PBS-X was carried out using chlorosulfonic acid(CSA) to obtain copolymers with various sulfonation levels(SPBS-X). All the synthesized compounds, monomers and polymers were characterized by $^1H$-NMR, $^{19}F$-NMR and FT-IR. It was confirmed that the ion exchange capacity(IEC), water uptake and ion conductivity of SPBS-X increased with the increment of sulfonated biphenyl units. Particularly, SPBS-60 showed higher ion conductivity compared to Nafion$^{(R)}$-115 at 25~80 $^{\circ}C$.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.171-177
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• 2011

PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes were prepared through the reaction polyvinyl alcohol (PVA) with glutaraldehyde (GLA) as a cross-linking agent and subsequently adding aluminum silicate ($Al_2O_3{\cdot}3SiO_2$) as an inorganic material. The water uptake decreased as the GDL contents increased due to cross-linking process of PVA with GDL, and the ion conductivity increased as the $Al_2O_3{\cdot}3SiO_2$ contents increased in PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes. The cross-linking structure of the polymers was confirmed using IR and the tendency of water uptake. The thermal analysis of the copolymers was carried out by TGA. TGA results showed that PVA/GLA composite membrane were more heat-resistant than PVA due to the cross-linking of PVA, and the heat stability of the composite membranes improved much more as the concentration of $Al_2O_3{\cdot}3SiO_2$ increased. Membranes prepared in this study seem to be have thermal stability and increase a tendency of the cation conductivity up to $60^{\circ}C$, but to be exhibit lower performance tendency at over $90^{\circ}C$. Therefore, it is necessary to do more aggressive effort to explore the possibility of application as an ion-conductive composite electrolyte.

• Journal of Biomedical Engineering Research
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• v.39 no.5
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• pp.220-228
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• 2018

The internal resistance of microbial fuel cell (MFC) using stainless steel skein for oxidizing electrode was investigated and the factors affecting the voltage generation were identified. We also investigated the effect of power management system (PMS) on the usability for MFC and the removal efficiency of organic pollutants. The performance of a stack microbial fuel cell connected with (PMS) or PMS+LED was analyzed by the voltage generation and organic matter reduction. The maximum power density of the unit cells was found to be $5.82W/m^3$ at $200{\Omega}$. The maximum current density was $47.53A/m^3$ without power overshoot even under $1{\Omega}$. The ohmic resistance ($R_s$) and the charge transfer resistance ($R_{ct}$) of the oxidation electrode using stainless steel skein electrode, were $0.56{\Omega}$ and $0.02{\Omega}$, respectively. However, the sum of internal resistance for reduction electrode using graphite felts loaded Pt/C catalyst was $6.64{\Omega}$. Also, in order to understand the internal resistance, the current interruption method was used by changing the external resistance as $50{\Omega}$, $300{\Omega}$, $5k{\Omega}$. It has been shown that the ohm resistance ($R_s$) decreased with the external resistance. In the case of a series-connected microbial fuel cell, the reversal phenomenon occurred even though two cells having the similar performance. However, the output of the PMS constantly remained for 20 hours even when voltage reversal occurred. Also the removal ability of organic pollutants (SCOD) was not reduced. As a result of this study, it was found that buffering effect for a certain period of time when the voltage reversal occurred during the operation of the microbial fuel cell did not have a serious effect on the energy loss or the operation of the microbial fuel cell.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.5
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• pp.382-391
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• 2009

Atmospheric speciated mercury concentrations including total gaseous mercury (TGM) and reactive gaseous mercury (RGM) were measured in Chuncheon from March 2006 to November 2008. Average concentrations were 2.10 ${\pm}$ 1.50 ng/$m^3$ and 3.00 ${\pm}$ 3.14 pg/$m^3$ for TGM and RGM, respectively. RGM concentrations were higher during daytime than nighttime probably because of high photochemical activities. We found that RGM concentration considerably increased as ozone increased when fog occurred, indicating that ozone was the important oxidant for $Hg^0$ in aqueous phase. TGM concentration showed positive correlations with CO and $PM_{10}$ which can transport in long-range, but there was no correlation with $NO_2$. Considering that major source of mercury is combustion process, this result showed that local sources did not significantly impact on TGM concentration in Chuncheon. Five-day backward trajectories were calculated for the samples representing high and low concentrations of TGM, and determined that industrialized area of China including Shenyang and Beijing influenced TGM concentrations in Chuncheon.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.1
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• pp.54-60
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• 2008

Deactivation of SCR catalyst applied in Orimusion fuel power plant was investigated to develope the technique for the regeneration of deactivated SCR catalyst and optimize the operation of SCR facility. The characterization study of the catalysts was carried out using XRD, ICP-AES, SEM and EDS. The NO$_X$ removal activity and SO$_2$ oxidation activity of the catalysts were measured. The NO$_X$ conversion of the deactivated catalyst was 5$\sim$10% lower than that of the fresh catalyst and the value of SO$_2$conversion to SO$_3$ over the deactivated catalyst was about 0.59% higher than that of the fresh catalyst. Vanadium(V), Magnesium(Mg) and Sulfur(S) were largely accumulated in the deactivated catalyst. The accumulation of Vanadium(V) and Sulfur(S) is due to the components of the Orimulsion fuel and the accumulation of Magnesium(Mg) is due to MgO that is injected in the boiler to prevent the oxidation of SO$_2$ to SO$_3$. The diffraction line of the TiO$_2$ of the deactivated catalyst was identified as the crystalline peaks of anatase as the fresh catalyst.