• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.374-380
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• 2015

In this paper, a dynamic model describing the 2 phase effect on the gas diffusion layer depending on load change of a fuel cell stack was developed to examine the effects of liquid water in fuel cell cathode gas diffusion layer on the fuel cell performance. For the developed model, 2 phase effect on the performance of a fuel cell stack depending on the load changes, concentration distribution of water vapor and oxygen inside a gas diffusion layer, the effect of the thickness and porosity of the gas diffusion layer on the fuel cell stack voltage were examined. As a result, a fuel cell stack voltage for the 2 phase model within the scope of the research become lower than that for the 1 phase model regardless of the load. Although oxygen molar concentration for the gas diffusion layer adjacent to the catalyst layer was the lowest, water vapor concentration is the highest. In addition, as thickness and porosity of the gas diffusion layer increased and decreased, respectively, the fuel cell stack voltage decreased.

• Analytical Science and Technology
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• v.21 no.3
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• pp.159-166
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• 2008

In this study, the characteristics of emulsified fuel and engine emissions were studied. Emulsified fuel which composed of water and diesel was manufactured by using homogenizer and ultrasonic generator. Engine emissions were studied whit engine dinamometer. In emulsified fuel, density and viscosity were increased with increasing water contents, but viscosity was decreased over 60% of water in emulsion fuel. The emulsion type of W/O changed to that of O/W over 60% of water in emulsion fuel. In the results of engine dinamometer test, NOx concentration and smoke density were reduced with increasing water contents in emulsified fuel but reciprocal in the case of THC, CO. Temperature and power were reduced with increasing water contents in emulsion fuel. In conclusion, it seemed that using emulsified fuel for diesel engine was effective for reducing NOx concentration and smoke density.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.2
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• pp.248-255
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• 2002

Miller cycle was studied and analyzed by engine performance simulation to achieve very low fuel consumption and to meet the IMO NOx regulation on a medium speed diesel engine. Based on the performance simulation results the intake valve closing time for HYUNDAI HiMSEN 6H21/32 engine was set at 0deg.ABDC(After Bottom Dead Center). Also, the simulation results indicated that significant NOx reduction could be achieved with low reduction of fuel consumption. The performance simulation investigated the effect of compression ratio and turbocharger on fuel consumption and NOx concentration in combination with Miller cycle. The results indicated a significant reduction of fuel consumption with keeping NOx concentration. The results of performance simulation were compared with measured data to verify simulation results. The comparison showed the maximum error was 2.34% in exhaust temperature. Also, the experimental result showed that improvement in BSFC(Brake Specific Fuel Consumption) was 5.8g/kwh with keeping NOx level similar to simulation result.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1099-1109
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• 2020

The performance of gadolinium burnable absorber (GdBA) for reactivity control in UO₂ and (U, Th)O₂ fuels and its impact on spent fuel characteristics was performed. Five fuel assemblies: one without GdBA fuel rod and four each containing 16, 24, 34 and 44 GdBA fuel rods in both fuels were investigated. Reactivity swing in all the FAs with GdBA rods in UO₂ fuel was higher than their counterparts with similar GdBA fuel rods in (U, Th)O₂ fuel. The excess reactivity in all FAs with (U, Th)O₂ fuel was higher than UO₂ fuel. At the end of single discharge burn-up (~ 49.64 GWd/tHM), the excess reactivity of (U, Th) O₂ fuel remained positive (16,000 pcm) while UO₂ fuel shows a negative value (-6,000 pcm), which suggest a longer discharge burn-up in (U, Th)O₂ fuel. The concentration of plutonium isotopes and minor actinides were significantly higher in UO₂ fuel than in (U, Th)O₂ fuel except for ²³⁶Np. However, the concentration of non-actinides (gadolinium and iodine isotopes) except for ¹³⁵Xe were respectively smaller in (U, Th)O₂ fuel than in UO₂ fuel but may be two times higher in (U, Th)O₂ fuel due to its potential longer discharge burn-up.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.49-56
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• 2023

The Polymer electrolyte membrane fuel cell (PEMFC) operates at ambient temperature as a low-temperature fuel cell. During its operation, voltage losses arise due to factors such as operating conditions and material properties, effecting its performance. Computational simulations of fuel cells can be categorized into 1D simulation and CFD, chosen based on their specific application purposes. In this study, we carried out an analysis validation using 1D geometry and compared its performance with the results from 2D geometry analysis. CFD allows for the representation of pressure, velocity distribution, and fuel mass fraction according to the geometry, enabling the analysis of current density. However, the 1D simulation, simplifying governing equations to reduce time cost, failed to accurately account for fuel distribution and changes in fuel concentration due to fuel cell operations. As a result, it showed unrealistic results in the cell voltage region dominated by concentration loss compared to CFD.

• Journal of Industrial Technology
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• v.17
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• pp.339-344
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• 1997

DOHC gasoline engine(4-cylinder in line type, 1600cc) is modified for the experiment to develope an alternative fuel. The modified engine is tested with the various combination of gasoline and methanol. Pollutant emissions of CO and HC are measured at the end of exhaust manifold. The concentration of CO and HC in exhaust gas is greatly reduced with the increase of coolant temperature of engine. HC concentration is reduced until methanol content reaches to thirty percent and then increased with the volumetric percentage of methanol in fuel. On the other hand, the concentration of CO is reduced as the methanol centent is increased up to 20 percent and then it becomes constant even though the methanol content is raised. The effect of engine RPM on the HC and CO exhaust is investigated. HC concentration is reduced as the engine RPM is increased but the typical trends of variation are not found in the measured value of CO concentrations.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.11-16
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• 2014

Although smoke emitted from ships is not included in IMO(International Maritime Organiztion) regulation yet, it is one of the substance what is polluting mainly the air. Especially, its concentration is very high when an engine is started and a load is rapidly changed. This is caused by unburned fuel what is injected more than necessary quantity after combustion period. It is possible to decrease smoke concentration emitted at starting engine by controlling fuel injection quantity, but it is concerned that time to rated speed must be spent. Then a governor what can reduce the smoke concentration without a loss of time to rated speed is needed. We adopted a electro-hydraulic governor what can control dual fuel start limit function and achieved very low level of smoke concentration without greater the loss of time to rated speed.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.6-10
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• 2008

The amount of methanol crossover was measured with changing the operating condition by using a liquid methanol concentration sensor. Appropriate operating condition was discussed in terms of methanol crossover. Mechanism of methanol crossover was classified into three items which are diffusion, convection and electro-osmosis. Contribution of each mechanism to methanol crossover and the effect of operating condition were analyzed with varying methanol concentration, pressure difference between anode and cathode, current, temperature, and stoichiometry of anode fuel. Among the three mechanisms diffusion affected mostly and electro-osmosis effect was observed only under high methanol concentration.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1358-1370
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• 2003

The effects of anode, cathode, and cooling channels for a Proton Exchange Membrane Fuel Cell (PEMFC) on flow fields have been investigated numerically. Continuous open-faced fluid flow channels formed in the surface of the bipolar plates traverse the central area of the plate surface in a plurality of passes such as a serpentine manner. The pressure distributions and velocity profiles of the hydrogen, air and water channels on bipolar plates of the PEMFC are analyzed using a two-dimensional simulation. The conservation equations of mass, momentum, and energy in the three-dimensional flow solver are modified to include electro-chemical characteristics of the fuel cell. In our three-dimensional numerical simulations, the operation of electro-chemical in Membrane Electrolyte Assembly (MEA) is assumed to be steady-state, involving multi-species. Supplied gases are consumed by chemical reaction. The distributions of oxygen and hydrogen concentration with constant humidity are calculated. The concentration of hydrogen is the highest at the center region of the active area, while the concentration of oxygen is the highest at the inlet region. The flow and thermal profiles are evaluated to determine the flow patterns of gas supplied and cooling plates for an optimal fuel cell stack design.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1222-1233
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• 1990

The formation and oxidation processes of soot particles in a diesel flame were investigated with a rapid compression machine. A cloud of soot particles was successfully visualized by means of the instantaneous laser shadow photographs technique and the equivalence ratio of the soot formation zone was estimated from a measured fuel concentration distribution in a nonevaporating spray. The temporal and spatial variation of soot concentration in the flame was also correlated with the rate of heat release. Soot particles appears first in a region near the flame tip when diffusion combustion period starts, and its concentration is a maximum at about the end of injection, then decreases due to oxidation. The reason for soot being formed in a fuel lean region near the flame tip is the evaporated fuel requires time to be pyrolized as it travels through the burning fuel rich zone towards the flame tip.