• Journal of Advanced Marine Engineering and Technology
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• 제33권8호
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• pp.1100-1106
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• 2009

최근, 디젤기관의 고효율달성을 위한 방법으로 밀러방식의 고팽창사이클에 대한 연구가 관심이 높다. 본 연구에서는 고팽창 디젤사이클을 구성하여 열역학적으로 해석하고, 몇몇 인자에 의한 사이클 특성을 분석하였다. 이론해석 결과 흡기밸브 닫힘시기가 지각될수록 유효압축비의 감소로 상대적인 팽창비의 효과는 커져 팽창-압축비의 비는 기대할 수 있었으나, 압축압력 및 흡입공기의 역류로 인해 평균유효 압력과 출력의 감고를 수반하였다. 따라서 이에 대한 대책이 있어야 진정한 의미의 고팽창 디젤사이클이 실현되고 열효율향상 가능성이 있음이 확인되었다. 위와 같은 사이클을 실제기관으로부터 구현하기 위해 흡기밸브 닫힘시기를 늦게 하는 제어시스템을 구축하고, 시험을 위해서 S/B가 약 3인 저속 단기통 디젤기관에 가변밸브타이밍(VVT)시스템을 적용하여 성능을 평가하였다. 그 결과 시험기관의 밸브제어에는 큰 문제없는 것으로 평가되었다.

• 한국자동차공학회논문집
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• 제1권2호
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• pp.17-26
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• 1993

As fundamental step to find the suitable compression ratio of hydrogen fueled engine, performance and combustion characteristics of that engine were analyzed. Qualitative characteristics of the hydrogen fueled engine were similar to that of the gasoline engine, and it was also found that knock limit compression ratio of the hydrogen fueled engine was higher than that of the gasoline engine.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.1001-1007
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• 2001

Hydrogen fueled engine with dual injection can achieve high power and high efficiency simultaneously. In this study, the suitable compression ratio of hydrogen fueled engine with dual injection were investigated including performance of this engine according to variation of compression ratio. As results, it was found that the suitable compression ratio of that was about CR=11, and torque and thermal efficiency increased by 6% and 7% respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3090-3095
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• 2008

In this study, variable compression ratio system(VCRS) was applied on the heavy-duty CNG engine and the characteristics of power and emission was investigated according to the increasing of compression ratio. As compression ratio increasing, the increasing of thermal efficiency in direct injection is three times higher than that in port injection. The emission of HC and CO in direct injection is reduced about 14.2%, 17.7% but NOx is increased because of increasing temperature in cylinder.

• Journal of Advanced Marine Engineering and Technology
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• 제30권1호
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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.

• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1141-1148
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• 2008

One of the methods to increase the efficiency of an engine is to expand pressures obtained from combustions equal to the pressure of atmosphere as much as possible and then convert thermal energy into mechanical energy also as much as possible. In this research, the Diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting Diesel engines to the Atkinson cycle, and general cycle features were analyzed after comparing these two cycles. In the case of fuel air the Diesel-Atkinson cycle considering intake and exhaust similar to real cycles, the value of thermal efficiency and average effective pressure increased, though their values were smaller than those of standard air amount cycle, when expansion compression ratio increased. When normal Diesel engines of which compression stroke and expansion stroke are all the same, was converted to the Atkinson cycle by changing the time of intake value close, combustion pressure reduced due to reduced expansion compression ratio and intake air amount due to decreased effective cycle volume.

• Journal of Advanced Marine Engineering and Technology
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• 제29권2호
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• pp.185-193
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• 2005

The present study composed a diesel-atkinson cycle of high expansion as a method of achieving high efficiency in diesel cycle engines. It also interpreted the cycle engine thermodynamically analysis to determine the possibility of the improvement of thermal efficiency and clarified the characteristics of several factors . According to the result of theoretical analysis, heat efficiency was highest when expansion-compression ratio Reど:1. In addition. diesel engines with high apparent compression ratio had higher expansion-compression ratio than otto engines and consequently their effect of high expansion was high. which in turn enhanced thermal efficiency. When the atkinson cycle was implemented in a real diesel engine by applying the miller cycle through the variation of the closing time of the intake valve, the effective compression ratio and the quantify of intake air decreased and as a result, the effect of high expansion was not observed. Accordingly. the atkinson 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 $4.1\%$ 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 diesel-atkinson cycle engine is realized.

• 한국수소및신에너지학회논문집
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• 제24권5호
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• pp.461-466
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• 2013

In this research, the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engine to the atkinson cycle, and general cycle features were analyzed after comparing these two cycles. That an experimental single cylinder and a long stroke diesel-atkinson engine, of which S/B ratio was more than 3, were manufactured. After evaluating the engine through basic experiments, a diesel engine was converted into the atkinson cycle by constituent VCR (variable compression ratio) device and VVT (variable valve timing) system. The experimental method was to observe compression work reduction effects due to low compression effects from delayed intake valve closing of the early stage atkinson engine. The result, the possibility of increasing compression ratio about each engine load was confirmation by constructing compensate expansion-compression ratio in accordance with the delayed intake valve close.

• Journal of Advanced Marine Engineering and Technology
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• 제35권8호
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• pp.1009-1015
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• 2011

본 연구에서는 고팽창사이클의 경우 가변밸브시스템을 구성하여 흡기밸브 닫힘시기를 늦추는 방식으로 실현하였고, 저압축에 따른 흡입공기의 감소는 과급압력으로 해결하였다. 이와 같이 디젤기관에 아트킨슨사이클을 실현하여 엔진의 열효율향상 가능성을 알아보았다. 그 결과 흡기밸브 닫힘시기 ABDC $40^{\circ}$ 부터 ABDC $80^{\circ}$ 까지 전 영역에 걸쳐 열효율 및 출력의 향상이 있었다. 다만, 흡기밸브 닫힘시기가 ABDC $70^{\circ}$이후로는 열효율 증가 폭이 둔화되는 경향을 보였다. 위와 같은 연구결과 저속 디젤-아트킨슨사이클화의 최적 연소조건은 흡기밸브 닫힘시기가 ABDC $70^{\circ}$전후로 보이며, 고부하영역이 저부하영역보다 더 효과적으로 나타났고, 중부하영역에서 기관운전은 안정적이었다. 이때 정미열효율은 통상의 디젤기관보다 평균 약 12.5% 높게 나타났다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.551-558
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• 2004

Recently, fuel prices have been continually raised in diesel engine. Such a change in the fuel price influences enormously the development trend of marine diesel engines for slow speed, In other words, the focus was shifted from large diameter and high speed to low fuel consumption. Accordingly, more efforts are being made for engine manufacturing and development to develop highly efficient engines. In this study. a single cylinder 4 stroke cycle DI slow speed diesel engine was designed and manufactured, a 4 stroke cycle was configured and basic performances were evaluated. The results are as follows. The optimal fuel injection timing had the lowest value when specific fuel consumption was in BTDC 8~$10^{\circ}$, a little more delayed compared to high speed diesel engines. Cycle variation of engines showed about 5% difference at full loads. This is a significantly small value compared to the cycle variation in which stable operation is possible, showing the high stability of engine operation is good. The torque and brake thermal efficiency of engine increased with an increase of engine 250-450 rpm. but fuel consumption ratio increased from the 450 rpm zone and thermal efficiency abruptly decreased. Mechanical efficiency was maximally 70% at a 400 rpm that was lower than normal engines according to the increase of mechanical frictional loss for cross head part. The purpose of this study was to get more practical engines by comparing the above results with those of slow speed 2 stroke cycle diesel engines.