• Journal of Hydrogen and New Energy
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• v.21 no.2
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• pp.98-103
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• 2010

In order to develop two-stroke free-piston hydrogen engine to obtain high thermal efficiency and low emission, backfire occurrence have to be prevented. In this research, backfire characteristics are analyzed as functions of the intake valve opening timing and compression chamber pressure under piston by using RICEM (Rapid Intake Compression Expansion Machine) that has reverse uni-flow scavenging. As the result, reverse uni-flow scavenging is advantage about back fire. but, it exists suitable intake valve opening timing and its timing become known that equivalence ratio 1 retard until the piston rises. Also, To rise chamber pressure of lower piston, this does not cause backfire occurs in equivalent ratio 0.6 observed back fire. Therefore, 2cycle hydrogen fueled free-piston engine is undesirable scavenging compression by compressing the piston.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.6
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• pp.745-752
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• 2003

Injection technology is one of the important technologies in a diesel engine. Many studies have done on the injection system. In this study, the fuel chamber geometry, the orifice ratio and the needle lift of the injection valve of a diesel engine for generating electricity are varied and tested. The injection pressure, duration and spray shapes are produced with pressure transducer, needle lift sensor and highspeed camera. The result shows that the nozzle hole size has influence on the rail pressure and injection duration sensuously.

• Journal of Chest Surgery
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• v.27 no.4
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• pp.272-280
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• 1994

Total 400 St.Jude Medical Bileaflet Valves were implanted in 336 pts from January 1983 to June 1993; 64 were aortic, 205 were mitral, 64 were double valve and 3 were tricuspid position. The follow up period extended from 6 months to 10 years[mean 24.3 months]. Male to female ratio was 1:1.7. There were total 27 deaths[cardiac related 20, cardiac non-related 7]. Overall mortality was 2.9%/pt-yr. There were 10 early deaths[3.0%] and 10 late cardiac related deaths [3.0%]. Prosthetic valve related complications occurred in 19 patients[5.7%] and among them, seven died; four died of thromboembolic events, two died of anticoagulants therapy related hemorrhagic complications and one died of bacterial endocarditis. NYHA class improved significantly especially in aortic valve replacement and double valve replacement. In AVR cases, the mean NYHA was 2.8 preoperatively and 1.3 postoperatively. And in DVR cases, 3.3 preoperatively and 2.2 postoperatively. The decision to employ a particular prosthesis was made according to the anticipated or known complications of the valve. The St.Jude Medical Valve retains all the hazards of other mechanical valves, most notably, thromboembolism. But the hemodynamic performance of St.Jude Medical Valve compared most favorably with other substitute valves in many reports. 0ur experience didn`t show any differences compared other authors in terms of valve related complication. So we concluded St. Jude Medical Valve can be primarily considered in the selection of artificial valve except in the patients when the usage of anticoagulant therapy is contraindicated.

• Journal of Chest Surgery
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• v.34 no.9
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• pp.680-685
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• 2001

Background: Tricuspid valve replacement is very rarely performed procedure and its long-term result is not yet satisfactory. Moreover, it is not well known whether bioprosthesis or mechanical prosthesis is the best selection for artificial valve. We reviewed 72 cases of tricuspid valve replacements in 71 patients between January 1989 and December 1998, trying to analyze the overall results and risk factors for mortality and morbidity. Material and Method: Average age of the patients at the time of operation was 42$\pm$13 years(range 16 to 65 years) and the sex ratio of male versus female was 32/39. Primary diagnosis consisted of 50 cases of aquired valvular heart disease and 18 cases of congenital heart disease, such as Ebstein’s anomaly. 4 cases had isolated tricuspid valve regurgitation. Implanted valves were 69 mechanical prosthesis and 3 bioprosthesis. Concomitant mitral or aortic valve replacements were performed in 50 cases. One patient received concomittant pulmonary valve replacement. Result: There were 7(9.72%) operative deaths and 7(13.0%) late deaths. Actuarial survival at 10 years was 59.2$\pm$7.2%. Prosthetic tricuspid valve thrombosis occurred 11 times in 5 patients. Reoperation for prosthetic tricuspid valve failure was performed in 1 patient. In this case, examination of the explanted prostheses showed that the tricuspid stenosis was the result of valve thrombosis. Among the 47 survivors, 46 patients(98%) were in functional class I or II. Conclusion: In our ten-year experience of tricuspid valve replacement, mortality and morbidity were satisfactory. Mechanical prosthesis in tricuspid position showed comparable clinical results as bioprosthesis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1185-1194
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• 2000

The characteristics of intake port flow and engine performance with swirl ratio variance in a turbocharged D.I. diesel engine were studied in this paper. The intake port flow is important factor which have influence on the engine performance and exhaust emission because the properties in the injected fuel depend on the combustion characteristics. Through these experiments it can be expected to satisfy performance and emission by optimizing the main parameters; the swirl ratio of intake port, injection timing and compression ratio. The swirl ratio for ports was modified by hand-working and measured by impulse swirl meter. For the effects on performance and emission, the brake torque and brake specific fuel consumption were measured by engine dynamometer, NOx and smoke were measured by gas analyzer and smoke meter. The results of steady flow test are as follows; as the valve eccentricity ratio are closed to cylinder wall, the flow coefficient and swirl intensity are increased. Also we realized that there is a trade-off that the increase of swirl ratio decreases mean flow coefficient and increases the Gulf factor. And the optimum parameters to meet performance and emission through engine test are as follows; the swirl ratio 2.43, injection timing BTDC 13oCA and compression ratio 15.5.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.3
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• pp.24-32
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• 1995

The scavenging characteristics have a great influence on the performance of a diesel engine, especially slow-speed two-stroke diesel engines which are usually used as a marine propulsion power plant, and they are greatly affected by the conditions in the cylinder, intake and exhaust manifolds, and the opening and closing timing of scavenging ports or exhaust valves during the gas exchange process. Besides, there are many other factors to affect the scavenging characteristics and these factors interact each other very complicatedly. Therefore the simulation program of the gas exchange process is very useful to improve and predict the scavenging characteristics, due to the high costs associated with redesign and testing. In this paper it was attenpted to investigate the effect of the variation of the pressure ratio of intake to exhaust manifolds, and the variation of the opening and closing timing of a exhaust valve by using a computational program for a three-zone scavenging model which was developed by authors. The computed results showed that the scavenging efficiency and delivery ratio increased considerably, but the trapping efficiency decreased with increasing of the pressure ratio of intake to exhaust manifolds. The scavenging efficiency, trapping efficiency, and th conditions of the cylinder gases were affected by the opening timing of the exhaust valve, but the delivery ratio by the closing timing.

• Journal of the Korean Society of Combustion
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• v.14 no.3
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• pp.37-44
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• 2009

An experimental study was conducted to reduce NOx emission in RT(radiant tube)burner by using oscillating combustion processes in RIST. A solenoid valve gives the various oscillating conditions, such as oscillation frequency, duty ratio of fuel flow. In this study, we used commercial software, CFD-ACE+ to predict combustion and NOx emission characteristics for various experimental oscillation conditions. The effect of oscillation frequency and duty ratio on NOx emission will be discussed in terms of flow field, temperature and equivalence ratio distributions in detail.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2961-2966
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• 2007

When the pressure at the weak spot established at a certain part of a high pressure vessel or piping system exceeds a design pressure, this weak spot is burst, and the pressurized gas emitted through the weak spot will cause a compression wave system. In this connection, in the present study, an experimental study by using a conventional shock tube facility is performed to estimate the effects of the material of diaphragm, curvature radius and thickness of materials on the valve opening time in diaphragm. Pressure sensor having 500kHz in natural frequency is installed at 35mm downstream of the rupture diaphragm to measure the static pressure history of propagating and being accumulated compression wave. 4 kinds of materials are used as diaphragm that is aluminium, copper, stainless steel and zinc. The diaphragm radii of curvature R are ${\infty}$, 120mm and 60, respectively. And the depth for $90^{\circ}$ groove is 0.04mm. It is found that the smaller the tensile strength and elongation of the rupture diaphragm is, the smaller the radius of curvature of the rupture diaphragm is, and for the same conditions the thinner the thickness of the rupture diaphragm is, the shorter the valve opening time becomes. Also, the tensile strength, elongation and the radius of curvature of the rupture diaphragm for the same conditions are smaller, the maximum pressure rise caused by the coalescences of the compression wave is smaller. Finally the pressure ratio is higher, the valve opening time is shortened and gradient of pressure increment is more steepen.

• Journal of Chest Surgery
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• v.10 no.2
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• pp.315-326
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• 1977

From 1958 to October 1977, 294 cases of acquired heart disease were operated. There were 68 cases of pericardium, 3 trauma, 2 foreign body, one cardiac thrombus, 3 atrial myxoma, 2 left atrial and 1 right atrial, 2 Budd-Chiari syndrome, and 214 valvular heart disease. Out of 214 cases of valve operation 73 valves were replaced in 64 patients. Male to female ratio was 1.46: 1. The youngest age was 14 years in male and 18 in female. The oldest was 54 years in male and 52 in female. Fifty-five cases of single valve were replaced, consisting of 47 mitral and 8 aortic valves. There were 9 double valve replacement cases which consist of 7 mitral and aortic and 2 mitral .and tricuspid valves. Six varieties of prosthetic valves, 3 ball and 3 disc types and 3 kinds of xenograft tissue valves were utilized. Beall, BjSrk-Shiley and Starr-Edwards prosthetic valves and Hancock valves were used mainly. For single valve 34. 5% and for double valve replacement 44% mortality were noted. There were 23 operative deaths out of 64 patients, over all mortality rate of 36.9%. Mortality for mitral valve replacement was 29.5%. But in recent 12 consecutive cases one death occurred, showing 8.3% mortality. In earlier days thrombocyte anti-adhesive drug dipyramidole-persantin-aspirin and/or SP 54 were adminstered. But in recent cases after heparinization, coumadin and Persantin were prescribed routinely.

• Journal of Chest Surgery
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• v.51 no.1
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• pp.15-21
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• 2018

Background: Prosthetic valve endocarditis (PVE) is a serious complication of cardiac valve replacement, and many patients with PVE require reoperation. The aim of this study was to review our institutional 20-year experience of surgical reoperative valve replacement in patients with PVE. Methods: A retrospective study was performed on 84 patients (mean age, $54.8{\pm}12.7years$; 51 males) who were diagnosed with PVE and underwent reoperative valve replacement from January 1995 to December 2016. Results: PVE was found in 1 valve in 61 cases (72.6%), and in 2 or more valves in 23 cases (27.4%). The median follow-up duration was 47.3 months (range, 0 to 250 months). Postoperative complications occurred in 39 patients (46.4%). Reinfection occurred in 6 cases, all within 1 year. The freedom from reinfection rate at 5 years was $91.0%{\pm}3.5%$. The overall survival rates at 5 and 10 years were $64.4%{\pm}5.8%$ and $54.3%{\pm}7.3%$, respectively. In stepwise multivariable Cox proportional hazard models, older age (hazard ratio [HR], 1.48; 95% confidence interval [CI], 1.05 to 2.10; p=0.027) and cardiopulmonary bypass (CPB) time (HR, 1.03; 95% CI, 1.00 to 1.01; p=0.033) emerged as independent risk factors for death. Conclusion: Older age and a longer CPB time were associated with an increased risk of overall mortality in PVE patients.