• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1009-1015
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• 2011

In this study, in the high expansion cycle was conduced by variable valve timing system composition to close intake valve late, and in the intake air reduction on the low compression was solved by supercharging pressure. In this wise, by constituting Diesel-Atkinson cycle, this study looked into a possibility of thermal efficiency improvement. As a result, there was improvement in thermal efficiency and output in a whole range of closing timing from ABDC $40^{\circ}$ to ABDC $80^{\circ}$. However, after ABDC $70^{\circ}$ of closing timing, the thermal efficiency increase was getting smaller. As the result of the study, the optimum intake valve closing timing was about ABDC $70^{\circ}$, high loading territory of engine was more effective than low loading territory, and engine operation in middle loading territory was stable. At this time, brake thermal efficiency was 12.5% higher than ordinary engine on average.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.86-94
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• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60$^{\circ}$ ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90$^{\circ}$shroud valve was larger than that of 120$^{\circ}$shroud valve, and 90$^{\circ}$shroud valve at 180$^{\circ}$shroud position had the largest turbulent intensity.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.40-40
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• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60° ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90°shroud valve was larger than that of 120°shroud valve, and 90°shroud valve at 180°shroud position had the largest turbulent intensity.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.4
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• pp.325-331
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• 2003

This paper described the characteristics of the exhaust pressure and proposed the assistant device for detection of misfired cylinder. Misfire, one of abnormal combustion, affects a bad influence of the 3-way catalyst and emits unburned hydrocarbon. Therefore, to prevent these unusual phenomena and eliminate the factor of the environmental pollution, early detection and correction of the misfired cylinder play a very important role. The configuration of assistant device was changed by length and diameter of pipe and analyzed with the install position on the exhaust system. Experimental results showed that the configuration of assistant device is not affected more than length and diameter of pipe and the assistant device is be effective in the detection of misfired cylinder on the gasoline engine.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.3
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• pp.27-34
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• 1997

The effects of the intake and exhaust valve timing to improve the engine performance in a spark ignition 3-cylinder LPG engine with a closed loop fuel supply system were studied. The engine torque and power have been measured using the 75kW EC-dynamometer while adjusting the optimal fuel consumption ratio with a solen- oid driver. As the results from this experiment, when intake valve opening is $12^{\circ}$ BTDC, intake valve closing is $36^{\circ}$ ABDC, exhaust valve opening is $12^{\circ}$ ATDC, and exhaust valve closing is $36^{\circ}$ BBDC respectively, the best torque characteristics in low and high speeds for a gives engine were obtained. And also we could find that the torque characteristics in low speeds were affected by the timing of exhaust valve open. An increased valve overlap by the EVC delay was ineffectual to the torque characte- ristics improvement in high speeds.

• 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.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.5
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• pp.1-11
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• 2004

In order to recognize thermal efficiency and power improvement in case that diesel cycle is turned into diesel-atkinson cycle, the fuel-air diesel-atkinson cycle considered gas exchange process is analyzed non-dimensionally and thermodynamically. As a result, in case of diesel-atkinson cycle, as expansion ratio is increased, thermal efficiency and mean effective pressure is increased and it has maximum value at Rec=1. When diesel cycle is turned into diesel-atkinson cycle by late intake valve closing timing, thermal efficiency and power is decreased because of the decline of effective compression ratio and intake airflow, but it could be compensated by increase of compression ratio or super-charged. In case compression ratio is compensated, Rec appears 1 around 100$^{\circ}$ ABDC, and it is expected that thermal efficiency is enhanced by 14.3% compared with conventional diesel cycle. In case compression ratio and intake airflow are compensated simultaneously, super-charged pressure is demanded 2.06bar at Rec=1 and it is more efficient when only compression ratio is compensated in the view point of thermal efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.6
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• pp.835-842
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• 2009

The present thesis carried out a research on a compression pressure's reduction phenomenon and its countermeasure according to the thermal efficiency improvement method by a Miller method in 4-cycle low speed diesel engine. In case of retardation of intake valve closing time in a engine, the theoretical heat efficiency shows a remarkably reducing trend when a compression ratio is not compensated. Accordingly, the thermal efficiency showed an increasing trend in case of compensating the compression ratio. Especially, it could be understood that the theoretical heat efficiency at near ABDC $100^{\circ}$ of intake valve closing time in case of compensation of the compression ratio was improved by around 25.1%, and the mean effective pressure was also increased by around 18.6%. Also, as the retardation of intake valve closing time increases, air quantity becomes insufficient due to a backflow phenomenon of intake air and thus thermal efficiency was decreased in a high load operation domain. The solving method of this problem is possible by supercharge. Therefore, in order to improve thermal efficiency by retardation of ntake valve closing time, the thermal efficiency improvement according to low compression is possible when there are a compensation device of a compression ratio and a supercharge device. This is a problem-solving method of low compression and high expansion cycle.