• Journal of ILASS-Korea
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• v.17 no.3
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• pp.140-145
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• 2012

Recent common-rail injector of a diesel engine needs more smaller nozzle hole to meet the stringent emission regulation. But, small nozzle hole diameter can cause nozzle coking which is occurred due to the deposits of post-combustion products. Nozzle coking has a negative effect on the performance of fuel injector because it obstructs the fuel flow inside a nozzle hole. In this study DFSS (Design for six sigma) method was applied to find the effect of nozzle design parameter on nozzle coking. Total 9 injector samples were chosen and tested at diesel engine. The results show that nozzle hole diameter and K-factor have more effect on nozzle coking than A-mass and hole length. Large hole diameter and A-mass, small hole length and K-factor give more positive performance on nozzle coking in these experimental conditions. But, a performance about nozzle coking and exhaust gas emission shows the opposite tendency. Further study is needed to find the relation between nozzle coking and emission characteristic for the optimization of injector nozzle design.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.3
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• pp.149-157
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• 2010

The electromagnetic characteristics of FCEVs (fuel cell electric vehicles) are much different from the existing combustion engine cars as well as hybrid, plug-in-hybrid, and pure electric vehicles due to the high voltage/current generated by a fuel cell stack which uses a compressed hydrogen gas reacted with oxygen. To operate fuel cell stack efficiently, BOP (Balance of Plant) is essential. BOP systems are used many not only for motors in water pump, air blower, and hydrogen recycling pump but also inverters for these motors. Since these systems or components are connected by high voltage cables, EMC (Electromagnetic compatibility) analysis for high voltage/current cable is the most important element to prevent the possible electric functional safety errors. In this paper, electromagnetic fields of high current/voltage cable for FCEVs is studied. From numerical analysis results, time harmonic magnetic field strength of high current/voltage cable have difference of 20～28 dB according to phase. EMI result considered ground effect of FECV at 10 m shows difference of 14.5 dB at 30 MHz and 2.8 dB at 230 MHz compared with general cable.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.631-636
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• 2018

This paper proposed an optimal operation strategy for a hybrid energy storage system (HESS) with a lithium-ion battery and lead-acid battery for mild hybrid electric vehicles (mild HEVs). The proposed mild HEV system is targeted to mount the electric motor and the battery to a conventional internal combustion engine vehicle. Because the proposed mild HEV includes the motor and energy storage device of small capacity, the system focuses on low system cost and small size. To overcome these limitations, it is necessary to use a lead acid battery which is used for a vehicle. Thus, it is possible to use more energy using HESS with a lithium battery and a lead storage battery. The HESS, which combines the lithium-ion battery and the secondary battery in parallel, can achieve better performance by using the two types of energy storage systems with different characteristics. However, the system requires an operation strategy because accurate and selective control of the batteries for each situation is necessary. In this paper, an optimal operation strategy is proposed considering characteristics of each energy storage system, state-of-charge (SOC), bidirectional converters, the desired output power, and driving conditions in the mild HEV system. The performance of the proposed system is evaluated through several case studies with respect to energy capacity, SOC, battery characteristic, and system efficiency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.71-74
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• 2010

Using the technology demonstration model of 75-tonf-class combustor which is expected to be used to the rocket engine of a korean space launch vehicle, 2 times of firing tests were carried out. Firing tests were done at 50% of the nominal flow rate because of incapability of the test facility and limit of the test bed strength. Through the low pressure firing tests of 75-tonf-class channel cooling thrust chamber, reliability and stability at the ignition and combustion phases were confirmed. Additionally it was foreseen that the 75-tonf-class thrust chamber would satisfy the performance requirements.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.617-621
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• 2017

The performance characteristics of aluminized high explosive are considered by varying the aluminum(Al) concentration in a two-phase model. Since the time scales of the characteristic combustion process of high explosives and Al particles differ, the process of energy release behind the leading detonation wave front occurs over an extended period of time. Two cardinal observations are reported: a decrease in detonation velocity with an increase in Al concentration and a double front detonation (DFD) feature when anaerobic Al reaction occurs behind the front. In the current study, a series of confined rate sticks are considered for characterizing the performance of aluminized HMX with a maximum Al concentration of 50%. The simulated results are compared with the experimental data for 5%-25% concentrations.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.291-293
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• 2015

The experimental study on flow characteristic in various laminar coflow diffusion flame has been conducted with a particular focus on the buoyancy force exerted from gaseous hydrocarbon fuels. Methane ($CH_4$), Ethylene ($C_2H_4$) and n-Butane ($C_4H_{10}$) were used as fuels. Coflow burner and Schlieren technique were used to observe the fuel flow field near nozzle exit and flow characteristics in flames. The result showed that the vortices in n-Butane with density heavier than air were appeared near the nozzle exit with the strong negative buoyancy on the fuel stream. As Reynolds number increases by the control of velocity, the vortices were greater and the vortices tips were moved up from the nozzle exit. In addition, it can be found that the heated nozzle can affect to the flow fields of fuel stream near the nozzle exit.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.275-278
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• Journal of the Korea Institute of Building Construction
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• v.18 no.6
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• pp.559-567
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• 2018

In the case of fire, surface treatment agents used in external insulation finishing methods are substances that are vulnerable to fire due to thin finishes and the combustion of polymers. In this study, it was expected that the performance of surface preparation mortars could be improved by using expandable graphite with excellent thermal performance. Experimental results showed that the mechanical properties of surface preparation mortar were improved by using the fly ash and silica fume. Surface treatment materials using expanded graphite have a characteristic of expanding when a fire occurs. It has been shown that heat-swellable surface treatment materials can reduce the penetration of heat sources into the surface of synthetic insulation.

• Journal of the Korean Wood Science and Technology
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• v.30 no.3
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• pp.18-25
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• 2002

Research to discuss the fire performance of materials requires tools for measuring their burning characteristics and validated fire growth models to predict fire behavior of the materials under specific tire scenarios using the measured properties as input for the models. In this study, burning characteristics such as time to ignition, weight loss rate, flame spread, heat release rate, total heat evolved, and effective heat of combustion for four types of wood-based materials were evaluated using the cone calorimeter and inclined panel tests. Time to ignition was affected by not only surface condition and specific gravity of the tested materials but also the type and magnitude of heat source. Results of weight loss rate, measured by inclined panel tests, indicated that heat transfer from the contacted flame used as the heat source into the inner part of the specimen was inversely proportional to specific gravity of material. Flame spread was closely related with ignition time at the near part of burning zone. Under constant and severe external heat flux, there was little difference in weight loss rate and total heat evolved between four types of wood-based panels. More applied heat flux caused by longer ignition time induced a higher first peak value of heat release rate. Burning characteristics data measured in this study can be used effectively as input for fire growth models to predict the fire behavior of materials under specific fire scenarios.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.116-117
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• 2021

In general, when a building fire occurs, the heat flow rises by buoyancy, which affects the temperature rise of the ceiling. In addition, when the ceiling ignites, the fire spreads rapidly due to horizontal spread and radiant heat. According to the fire investigation, most of the large fires have a common characteristic that the fire spreads to the ceiling and causes many casualties. Therefore, it is considered that it is necessary to review the fire risk of ceiling materials used in buildings to prevent the spread of fire to the ceiling. Therefore, in this study, combustion characteristics such as the amount of heat released and ignition time of each SMC, DMC, and gypsum board were checked using a Cone Calorimeter, and the ignition temperature was calculated by substituting them into the fire theory. As a result, the ignition temperature of SMC was 449K, that of DMC was 1492K, and that of gypsum board was 677K.