• Journal of Hydrogen and New Energy
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• v.19 no.6
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• pp.474-481
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• 2008

수소 기관에서 역화없이 고성능과 저$NO_x$를 실현시키기 위하여 밸브 타이밍 변화에 따른 흡기관 분사식 수소 기관의 성능을 파악하고 가솔린의 경우와 비교하였다. 그 결과 흡기밸브 타이밍은 역화억제와 성능향상에 큰 영향을 미치는 것을 확인하였다. 흡기밸브타이밍의 진각은 역화를 억제하며 효율과 출력을 동시에 향상된다. 비록 흡기밸브 타이밍 변화에 의해 NOx는 증가하지만, 희박영역인 출 ${\Phi}=0.5$에서 현저히 감소된다. 또한 열효율은 ${\Phi}=0.5$ 토크는 ${\Phi}=1.0$에서 가장 높게 나타난다. 흡기밸브 타이밍을 $ATDC20^{\circ}$에서 TDC로 변화시켰을 때, ${\Phi}=1.0$에서 토크는 약 28% 증가되고, ${\Phi}=0.5$에서 효율은 약 7%향상된다.

• Journal of ILASS-Korea
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• v.25 no.2
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• pp.45-50
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• 2020

Recently, global warming and environmental pollution are becoming more important, and fuel economy is becoming important. Each automobile company is actively developing various new technologies to increase fuel efficiency. CVVD(Continuously Variable Valve Duration) system means a device that continuously changes the rotational speed of the camshaft to change the valve duration according to the state of the engine. In this paper, VVT(Variable Valve Timing) and CVVD were applied to a single-cylinder diesel engine, and the characteristics of intake and exhaust flow rate and in-cylinder pressure characteristics were analyzed by numerical analysis. In order to analyze the effect of CVVD on the actual engine operation, the study was performed by setting the valve control and injection pressure as variables in two sections of the engine operating region. As a result, In the case of applying CVVD, the positive overlap with the exhaust valve is maintained, thus it is possible to secure the flow smoothness of air and increase the volumetric efficiency by improving the flow rate. The section 2 condition showed the highest peak pressure, but the pressure rise rate was similar to that of the VVT 20 and CVCD 20 conditions up to 40 bar due to the occurrence of ignition delay.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.690-691
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• 2006

Variable valve timing unit, which is able to decrease environmental load and improve fuel economy is loaded onto many automobiles recently. This unit consists mainly of sprocket, housing and rotor. These parts are requested different properties according to environment. We produce sintered parts for variable valve timing unit by selecting compact, sinter process and special treatment according to demanded properties. In this paper, demanded properties of sintered parts for variable valve timing unit and adopted technique to satisfy them are presented.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1100-1106
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• 2009

Recently, there are quite a lot of attention is drown on the researches related to of Miller method applied high expansion cycle. For this study, high expansion cycles are formed and analyzed with the base view point of thermodynamics, and the features of each factors are also investigated. As a result of analysis, the expansion-compression ratio is expected with a decrease of effective compression ratio as intake valve closing time retarded, however, the decrease of mean effective pressure and its output is accompanied with the counterflow of intake air. Accordingly, as the consequence of such failure, it is expected that an alternative is needed for the realization of high expansion cycles, and the improvement over thermal efficiency. To materialize such cycle, the control system to delay the closing time of intake valve was designed and VVT, the 3 S/B low speed diesel engine, is applied to evaluate the efficiency. The result of the trial shows that there was no significant errors.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.9
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• pp.82-88
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• 1999

The object of this study is to find new evaluation index for in-cylinder flow chracteristics istead of current swirl, tumble coefficient using steady flow test rig on intake port system. To this end, port flow system. To this end, port flow rig test was conducted on DOHC head varying intake valve lift respectively. Finally combination angular coefficient and inclination angle were introduced as new evaluation index for in-cylinder angularflow characteristics instead of swirl and tumble coefficient.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.6
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• pp.24-29
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• 2001

Adaptive valve timing control is one of the promising techniques to accomplish the optimized mixture formation and combustion depending on the load and speed, which is needed to meet the future challenges in reducing fuel consumption and exhaust emissions. The behavior and the effect of adaptive valve timing control system has been investigated by computer simulation, which simulates the gas dynamics in engines. Improved fuel economy can be achieved by reduction of pumping loss under low and mid load conditions. EIVC(Early Intake Valve Closing) strategy turns out to be superior to LIVC(Late Intake Valve Closing) strategy in reducing fuel consumption. Deterioration of combustion quality can be overcome by introducing LIVO(Late Intake Valve Opening) strategy, which increases turbulent intensity in cylinders. Furthermore, LIVO can reduce HC emission by decreasing the required amount of fuel to be injected during cold start.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.357-369
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• 2003

Electromagnetic valve (EMV) actuation system is a new technology for improving fuel efficiency and at the same time reducing omissions in internal combustion engines. It can provide more flexibility in valve event control compared with conventional variable valve actuation devices. The electromagnetic valve actuator must be designed by taking the operating conditions and engine geometry limits of the internal combustion engine into account. To help develop a simple design method, this paper presents a procedure for determine the basic design parameters and dimensions of the actuator from the relations of the valve dynamics, electromagnetic circuit and thermal loading condition based on the lumped method. To verify the accuracy of the lumped method analysis, experimental study is also carried out on a prototype actuator. It is found that there is a relatively good agreement between the experimental data and the results of the proposed design procedure. Through the whole speed range, the actuator maintains proper performances in valve timing and event control.

• Journal of Korean Elementary Science Education
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• v.17 no.2
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• pp.103-111
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• 1998

The purpose of this study was to investigate the relationship among spatial ability, learning styles, visual-perception- recall abiltiy, and the conceptual construction of the earth and moon's motion. Four paper-and-pencil tests were used to measure students' cognitive variables. Spatial ability was measured by Spatial Visualization Test, visual-perception-recall ability was measured by Rey's Figure which also have used to test visual- perception-recall ability of right-temporal lobes, and VVT were used to investigate students' learning styles. further, the test of concept construction was consisted of 15 items about the earth and moon's motion developed by researcher One hundred and twenty-seven 6th-, one hundred and sixteen 7th-, eighty-seven 9th-grade, ninety-three college students were participated in the investigation of the effects of age and learning style on conceptual construction. In the analysis of students' performances, spatial ability, visual-perception-recall ability, and conceptual achievement showed an increasing pattern with grading. In addition, visual learner's conceptual achievement showed a significantly higher score on conceptual test than verbal learner's(p<0.05). The results of the present study supported tile hypothesis that learning styles would differently influence to learning atmospheric concepts by students'learning styles. This study also indicated to be considered the students' spatial ability in learning atmospheric concepts.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.42-49
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• 2006

In this research. the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engines to the high expansion diesel cycle, and general cycle features were analyzed after comparing these two cycles. Based on these analyses. an experimental single cylinder a long stroke with high expansion-diesel engine. of which S/B ratio was more than 3, was manufactured. After evaluating the base engine through basic experiments, a diesel engine was converted into the high expansion diesel engine by establish VCR device and VVT system Accordingly, the high expansion diesel cycle can be implemented when the quantity of intake air is compensated by supercharge and the effective compression ratio is maintained at its initial level through the reduction of the clearance volume. In this case, heat efficiency increased by $5.0\%$ at the same expansion-compression ratio when the apparent compression ratio was 20 and the fuel cut off ratio was 2. As explained above, when the atkinson cycle was used for diesel cycle, heat efficiency was improved. In order to realize high expansion through retarding the intake value closing time, the engine needs to be equipped with variable valve timing equipment, variable compression ratio equipment and supercharged pressure equipment. Then a high expansion diesel cycle engine is realized.

• International Journal of Automotive Technology
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• v.7 no.7
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• pp.763-768
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• 2006

Emission reduction in the cold start period of SI engines is crucial to meet stringent emission regulations such as SULEV Emissoin reduction is the starting point of the study in the which the variable valve timing (VVT) technology may be one promising method to minimize cold start emissions while maintaining engine performance. This is because it is possible to change valve overlap and residual gas fraction during cold start and idle operations. Our previous study showed that spark timing is another important factor for reducing cold-start emissions since it affects warm-up time of close-coupled catalysts (CCC) by changing exhaust gas temperature. However, even though these factors may be favorable for reduction of emissions, they may deteriorate combustion stability in these operating conditions. This means that the two variables should be optimized for best exhaust emissions and engine stability. This study investigated the effects of valve and spark timings in idle performance such as combustion stability and exhaust emissions. Experiments showed that valve timings significantly affected engine stability and exhaust emissions, especially CO and $NO_x$, due to change in residual gas fraction within the combustion chamber. Spark timing also affects HC emissions and exhaust gas temperature. Yet it has no significant effects on combustion stability. A control strategy of proper valve timing and spark timing is suggested in order to achieve a reduction in exhaust emissions and a stable operation of the engine in a cold start and idle operation.