• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.4
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• pp.93-100
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• 2009

Intake/exhaust valve timing and exhaust cam lift were changed to control the internal exhaust gas recirculation (IEGR) and combustion phase of homogeneous charge compression ignition (HCCI) engine. To measure the IEGR rate, in-cylinder gas was sampled during from intake valve close to before ignition start. The lower exhaust cam made shorter valve event than higher exhaust cam and made IEGR increase because of trapping the exhaust gas. IEGR rate was more affected by exhaust valve timing than intake valve timing and increased as exhaust valve timing advanced. In-cylinder pressure was increased near top dead center due to early close of exhaust valve. Ignition timing was more affected by intake valve timing than exhaust valve timing in case of exhaust valve lift 8.4 mm, while ignition timing was affected by both intake and exhaust valve timing in case of exhaust valve 2.5 mm. Burn duration with exhaust valve lift 2.5 mm was longer than other case due to higher IEGR rate. The fuel conversion efficiency with higher exhaust valve lift was higher than that with lower exhaust valve lift. The late exhaust and intake maximum open point (MOP) made the fuel conversion efficiency improve.

• International Journal of Automotive Technology
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• v.8 no.1
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• pp.19-25
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• 2007

This experimental study was carried out to obtain both low emissions and high thermal efficiency by rapid bulk combustion. Two kinds of experiments were conducted to obtain fundamental data on the operation of a RI engine by a radical ignition method. First, the basic experiments were conducted to confirm rapid bulk combustion by using a radical ignition method in a constant volume chamber (CVC). In this experiment, the combustion velocity was much higher than that of a conventional method. Next, to investigate the desirable condition of engine operation using radical ignition, an applied experiment was conducted in an actual engine based on the basic experiment results obtained from CVC condition. A sub-chamber-type diesel engine was reconstructed using a SPI type engine with controlled injection duration and spark timing, and finally, converted to a RI engine. In this study, the operation characteristics of the RI engine were examined according to the sub-chamber's specifications such as the sub-chamber volume and the diameter and number of passage holes. These experimental results showed that the RI engine operated successfully and was affected by the ratio of the passage hole area to the sub-chamber volume.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.5
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• pp.171-178
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• 2008

The combustion and exhaust emission characteristics were investigated in an DME fueled HCCI engine. Carbon dioxide, nitrogen and mixed gas, which was composed of carbon dioxide and nitrogen, were used as control parameters of combustion and exhaust emission. As the oxygen concentration in induction air, which was occurred by carbon dioxide, nitrogen and mixed gas, was reduced, the start of auto-ignition was retarded and the burn duration was extended due to obstruction of combustion and reduction of combustion temperature. Due to these fact, indicated mean effective pressure was increased and indicated combustion efficiency was decreased by carbon dioxide, nitrogen and mixed gas. In case of exhaust emission, hydrocarbon and carbon monoxide was increased by reduction of oxygen concentration in induction air. Especially, partial burning was appeared at lower than about 18% of oxygen concentration by supplying carbon dioxide. However it was overcome by intake air heating.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.457-464
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• 2006

Controlled auto ignition (CAI) combustion, also known as HCCI (homogeneous charge compression ignition), offers the potential to simultaneously improve fuel economy and reduce emission. CAI-combustion was achieved in a single cylinder gasoline DI engine, with a cylinder running in a CAI mode. Standard components were used the camshafts which had been modified in order to restrict the gas exchange process. The effects of air-fuel ratio, residual EGR rate and injection timing such as early injection and late injection on the attainable CAI combustion region were investigated. The effect that injection timings on factor such as start of combustion, combustion duration and heat release rate was also investigated. From results early injection caused the mixture to ignite earlier and burn more quickly due to the exothermic reaction during the recompression and gave rise to good mixing of the fuel-air.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.465-471
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• 2006

Controlled auto-ignition(CAI) combustion, offers the potential to improve fuel economy and reduce emission simultaneously. In this study, CAI-combustion was achieved in a single cylinder gasoline DI engine with modified camshafts in order to restrict the gas exchange process. We investigated the effects of air-fuel ratio, residual EGR rate and injection timing such as early injection and late injection on the attainable CAI combustion region. The effect of injection timings on combustion characteristic such as start of combustion, combustion duration and heat release rate was also investigated. From the result early injection causes the mixture to ignite earlier and burn more quickly due to the exothermic reaction during the recompression and gives rise to good mixing of the fuel/air. On the other hand, late injection extended the operation region more than early injection but the emissions of HC and NOx were more or less increased than early injection.

• Horticultural Science & Technology
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• v.16 no.3
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• pp.366-369
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• 1998

To lesson economical loss induced by fumigation in importing country when cut roses are exported, effects of several fumigation temperature, treatments of cut stems (dry or wet), methyl bromide (MB) concentrations, and fumigation periods on the quality of cut roses were investigated. According to results, the most important factor affecting the quality of cut rose was found to be fumigation temperature. When fumigated at $5^{\circ}C$, cut roses showed no chemical damages, e.g., tip burn or bent neck, and maintained their quality for the same duration as that of control, regardless of MB concentrations or treatments of cut stems. However, phytotoxicity by MB increased and vase life of cut rose was shortened as fumigation temperature increased. Timing of fumigation also appeared to be an important factor affecting the quality of cut roses of which phytotoxicity by MB was not observed and thier vase life was not shortened, even if MB was treated up to $40g{\cdot}m^{-3}$, when cut roses were fumigated at $5^{\circ}C$ on the day of harvesting. On the other hand, the degree of damage of cut flowers by fumigation methods or MB concentraions was not consistent with changes in fumigation temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.12
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• pp.950-958
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• 2013

The Lunar orbiter is expected to be inserted into a ~300km low Earth orbit using Korea Space Launch Vehicle-II(KSLV-II). After the states are successfully determined with obtained tracking data, the Trans Lunar Injection(TLI) burn has to be done at appropriate epoch to send the lunar orbiter to the Moon. In this study, we describe in detail the mission scenario of the Korean lunar orbiter from the launch at NARO Space Center to lunar orbit insertion(LOI) stage following direct transfer trajectory. We investigate the launch window including launch azimuth, delta-V profile according to TLI and LOI burn positions. We also depict the visibility conditions of ground stations and solar eclipse duration to understand the characteristics of the direct transfer trajectory. This paper can be also helpful not only for overall understanding of ${\Delta}V$ trend by changing TOF and coasting time but for selecting launch epoch and control parameters to decrease fuel consumption.

• Archives of Plastic Surgery
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• v.34 no.5
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• pp.593-598
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• 2007

Purpose: Talipes equinus deformity is defined as impossibility of heel weight-bearing and lacking of improvement of toe-tip gait despite sufficient duration of conservative treatment. The incidence of equinus deformity induces post-traumatic extensive soft tissue defect and subsequently increases it. Severe equinus deformities of the foot associated with extensive scarring of the leg and ankle were corrected using achilles Z-lengthening and free-tissue transfer. Methods: Free radial forearm flap was done in nine cases of eight patients from January 2000 to November 2006. Causes of deformity were post-traumatic contracture (one patient) and post-burn scar contracture (seven patients). Seven patients were male, one patient was female. Mean age was 32.1 (range, 10-57). Flap donors were covered with artificial dermis ($Terudermis^{(R)}$) and split thickness skin graft (five cases), and medium thickness skin graft only (four cases). Results: The size of flaps varied from $6{\times}12$ to $15{\times}12cm$ (average, $12{\times}7.8cm$). Achilles tendon was lengthened 4.2cm on average. Free radial forearm flap was satisfactory in all cases. All patients could ambulate normally after the surgery. Cases having donor coverage with $Terudermis^{(R)}$ were aesthetically better than those having skin grafts only. Conclusion: This study suggested that severe equinus deformities associated with extensive scarring of the leg and ankle can be corrected effectively free radial forearm flap and Achilles tendon lengthening.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.149-156
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• 2006

This paper investigates the steady state combustion characteristics of LPG homogeneous charge compression ignition(HCCI) engine with variable valve timing(VVT) and dimethyl ether(DME) direct injection, to find out the benefits in exhaust gas emissions. VVT is one of the attractive ways to control HCCI engine. Hot internal residual gas which is controlled by VVT device, makes fuel is evaporated easily, and ignition timing is advanced. Regular gasoline and liquefied petroleum gas(LPG) were used as main fuel and dimethyl ether(DME) was used as ignition promoter in this research. Operating range and exhaust emissions were compared LPG HCCI engine with gasoline HCCI engine. Operating range of LPG HCCI engine was wider than that of gasoline HCCI engine. The start of combustion was affected by the intake valve open(IVO) timing and the ${\lambda}TOTAL$ due to the latent heat of vaporization, not like gasoline HCCI engine. At rich operation conditions, the burn duration of the LPG HCCI engine was longer than that of the gasoline HCCI engine. CAD at 20% and 90% of the mass fraction burned were also more retarded than that of the gasoline HCCI engine. And carbon dioxide(CO2) emission of LPG HCCI engine was lower than that of gasoline HCCI engine. However, carbon oxide(CO) and hydro carbon(HC) emission of LPG HCCI engine were higher than that of gasoline HCCI engine.

• Archives of Reconstructive Microsurgery
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• v.3 no.1
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• pp.64-71
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• 1994

The successful treatment of the extensively traumatized foot warrants reconstruction utilizing tissue that will provide adequate coverage, is resistant to infection, thin enough to conform to the contours of the foot as well as durable to constant frictional movement and weight bearing. Currently, free flaps offer the best means in achieving these difficult and sometimes contradictory goals. We treated twenty-one patients suffering from extensive soft tissue loss of the foot due to trauma, electric burn or postburn sequelae with free flaps. A fasciocutaneous, musculocutaneous or muscle flap with skin grafting was used based on the location, volume of tissue required, and the functional anatomical requirement of the injured region. The follow-up duration averaged twenty-nine months. From our group of patients, we believe that the muscle free flap with skin grafting offers the most favorable outcome.