• 한국수소및신에너지학회논문집
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• 제26권1호
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• pp.28-34
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• 2015

HCCI (Homogeneous Charged Compression Ignition) hydrogen engine has relatively narrower operation range caused by backfire occurrence due to the rapid pressure rising by using higher compression ratio and significant reaction velocity. In this study, to grasp of backfire process and characteristic in the HCCI research hydrogen engine, in-cylinder pressure, intake pressure and backfire limit range are analyzed with compression ratio and intake valve open timing, experimentally. As the result, it is observed that knock is occurred just before backfire occurrence in HCCI hydrogen engine but not spark igntion type, this phenomenon is always the same for the above variables. Also backfire limit range are expanded up to 50% for the more retarding intake valve open timing in this operating conditions.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1181-1187
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• 2006

Stringent regulations of exhaust emission from vehicles become a major issue in automotive industries. In SI engines, it is one of the crucial factor to reduce exhaust emissions during cold start in order to meet stringent regulations such as SULEV or EURO-4, because SI engines emit a large portion of total harmful exhaust compounds when they are cold. At early stages of cold start in gasoline engines, exhaust gas temperature plays a key role to improve three way catalyst by virtue of fast warmup. Therefore, this study focused on the increase of exhaust gas temperature under controls of engine operating parameters such as spark ignition timing, valve overlap by virtue of intake VVT and catalyst heating function. Furthermore, effects on harmful emission due to these parameters are also investigated. Experiments showed that retarded spark ignition timings and increased valve overlap may be helpful to increase exhaust gas temperature. It was also found that $NO_x$ was decreased with increased valve overlap. This study also showed that sudden changes in ISA and amount of fuel due to the deactivation of catalyst heating function cause temporal increase of harmful emissions.

• Journal of Advanced Marine Engineering and Technology
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• 제29권7호
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• pp.801-807
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• 2005

Any failure of intake and exhaust valves of marine diesel engine must be regarded as serious, and any steps which can be taken to prevent such failure are desirable. The purposes of this study is to investigate and to analyse the failure causes of intake and exhaust valves for marine diesel engine during sea trial after completion of overhauling. In this study, to analyse the failure causes, we have carried out on board inspection, fractography test and discussion based on the specimen and repairing report provided by the ship owner. From the results of above inspection, test and discussion, it has been considered reasonable to conclude that the causes of damaged valves of the ship are as follow ; 1) During operation, the stick or seizure of valve spindle occurred and hence the movement of exhaust valve spindle was to be resisted and subsequently the engine was to be operated under an unappropriated valve timing and the exhaust valve sustained the repeated loads exceeding the fatigue strength of valve material. 2) By the loads above described, the fatigue fracture was initiated at the structural noncontinuous part of exhaust valve spindle, and then the valve head was finally fractured and dropped in the cylinder. 3) The fractured exhaust valve head impacted the intake valve at various direction to be bent or damaged.

• 한국자동차공학회논문집
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• 제14권4호
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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.

• 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 Chest Surgery
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• 제45권4호
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• pp.213-224
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• 2012

Tetralogy of Fallot (TOF) is an index lesion for all paediatric and congenital heart surgeons. In designing an appropriate operation for children with TOF, the predicted postoperative physiology must be taken into account, both for the short and long term. A favourable balance between pulmonary stenosis (PS) and pulmonary insufficiency (PI) may be critical for preservation of biventricular function. A unified repair strategy to limit both residual PS and PI is presented, along with supportive experimental evidence. A strategy for dealing with coronary anomalies and some comments regarding best timing of operation are also included.

• Journal of Biosystems Engineering
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• 제31권1호
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• pp.39-45
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• 2006

Fundamental informations on performance of sets of solenoid valve and nozzle were necessary to develop a target selectable spraying system. The experiments were performed for the sets of solenoid valves and flat spraying nozzles at 3 levels of the operating pressures, and the obtained results are as follows; Rise time of the system pressure to reach up to 90% of the operating pressure after the valve turned was affected by nozzle size and operating pressure. Maximum overshoot of the system pressure was about 170% not affected by the sets of valve and nozzle and operating pressure. The system pressure after its settle down within 5% of the set pressure showed good uniformity in any condition of the experiment as less as 2.3% of its coefficient of variation. Time requirement to lower the system pressure down to 50% after the valve power turned off was affected by valve and nozzle set and operating pressure.

• Journal of Chest Surgery
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• 제19권4호
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• pp.618-626
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• 1986

Univentricular heart is a rare congenital cardiac anomaly in which the atrial chambers are connected to only one ventricular chamber and it consists of a diverse group of cardiac malformation characterized by both AV valves or a common AV valve opening into the same ventricle, or the presence of only a solitary AV valve. In spite of recent development in cardiac surgery, corrective operations for univentricular heart still have high mortality and complication rate. Twenty eight patients underwent corrective operation for univentricular heart at Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital from February 1979 to July 1986. Of the 28 patients, 7 patients were operated on by ventricular septation and 21 patients by modified Fontan operation. Of the 28 patients, 19 patients were male and 9 patients female and ages ranged from 5 months to 18 years old with the average age of 7.3 years. There were 2 mortalities in 7 patients operated on by septation with the mortality rate of 28.6% and 5 complications, 3 complete AV block, 1 low cardiac output and 1 arrhythmia. All survived patients are being followed up without specific problem till now. There were 10 mortalities in 21 patients operated on by modified Fontan operation with the mortality rate of 47.6% and 10 complications, 2 low cardiac output, 2 respiratory failure necessitating tracheostomy, 2 persistent cyanosis, 2 arrhythmia, 1 missing of left AV valve in situs inversus patient due to misdiagnosis and one rupture of closed right AV valve. Incremental risk factors for operative mortality are young age less than 5 years old, anomalous pulmonary and systemic venous drainage and atrial septation procedure. In 11 survived patients, 9 patients show good follow-up results but one patient complains of persistent cyanosis and another one patient is suffered from CHF. In our series, results of corrective operation for univentricular heart shows continuing improvement but still high mortality and complication rate. So there must be continuing improvement in surgical result by selection of patient, by adequate decision making for timing and method of operation and by improving operative methods.

• Journal of Chest Surgery
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• 제21권2호
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• pp.254-269
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• 1988

52 cases of ventricular septal defect [VSD] associated with aortic insufficiency [Al] were found among 1271 patients with simple VSD operated during 27-year period [1959, August-1987, June] at Seoul National University Hospital. Their preoperative data, intraoperative findings and postoperative short-term and long-term follow-up data were evaluated to find the proper timing and method of surgical treatment. The result of this survey shows as follows: 1. To obtain the proper surgical indication, cardiac catheterization and angiography, especially root aortography, was essential. 2. Of all 52 patients, the VSD were type I in 40 patients [77%], type II in 8 [15%] and combination of type I and II in 4 [3%]. Patch closure of VSD were performed in 46 patients and direct suture closure of small VSD in 6. Most common pathologic findings of Al were prolapse of right coronary cusp [40 cases, 77%]. Aortic valve reconstruction were performed in 19 patients, aortic valve replacement in 6 and VSD closure alone in 27. 3. There were 3 surgical deaths [mortality 5.8%], and the long-term follow-up shows that VSD closure alone might have been sufficient to arrest progression of Al in younger patients [less than 10-year old], particularly in those with mild insufficiency. Valve reconstructions, when necessary, were more effective when done at an early age [less than 15-year old]. In a conclusion, we could recommend followings: 1. If patient at any age having VSD with Al is diagnosed, prompt operation is recommended. As for the surgical method, VSD closure only may be fit for mild degree of Al when patient is less than 10-year old, but the management of valve itself may be needed for moderate to severe degree of Al, especially when patient is over 10 year old. The management of valve itself may be variable, but valve reconstruction should be considered as a first choice in less than 15-year old patient. If patient is diagnosed less than 5-year old without evidence of Al, close follow-up observation is recommended. But if Al evidences of clinical findings and/or echocardiography during follow-up examination are notified, corrective operation should be accomplished while the Al is mild. If cusp prolapse and/or even type I VSD of significant size is demonstrated on aortogram, without Al, it should be corrected as early as possible before the patient is about 5 years old.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1451-1460
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• 2004

A two-stroke Schnurle-type gasoline engine was modified to enable compression-ignition in both the port fuel injection and the in-cylinder direct injection. Using the engine, examinations of compression-ignition operation and engine performance tests were carried out. The amount of the residual gas and the in-cylinder mixture conditions were controlled by varying the valve angle rate of the exhaust valve (VAR) and the injection timing for direct injection conditions. It was found that the direct injection system is superior to the port injection system in terms of exhaust gas emissions and thermal efficiency, and that almost the same operational region of compression-ignition at medium speeds and loads was attained. Some interesting combustion characteristics, such as a shorter combustion period in higher engine speed conditions, and factors for the onset of compression-ignition were also examined.