• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.113-121
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• 1994

Since two oil shocks in 1970s, all of engine makers have persevered in their efforts to reduce specific fuel consumption and to increase engine power rate as much as possible in marine diesel engines. As a result, the maximum pressure in cylinders of these engines has been continuously increased. It causes direct axial vibration. The axial stiffness of crank shaft is low compared to old types of engine models by increasing the stroke/bore ratio and its major critical speed might occur within engine operation range. An axial damper, therefore, needs to be installed in order to reduce the axial vibration amplitude of the crankshaft. Usually the main critical speed of axial vibration for the propulsion shafting system with a 4-8 cylinder engine exists near the maximum continuous revolution(MCR). In this case, when the damping coefficient of the damper is increased within the allowance of the structural strength, its stiffness coefficient is also increased. Therefore, the main critical speed of axial vibration can be moved beyond the MCR. It has the same function as a conventional detuner. However, in the case of a 9-12 cylinder engine, the main critical speed of axial vibration for the propulsion shafting system exists below the MCR and thus the critical speed cannot be moved beyond the MCR by using an axial damper. In this case, the damping coefficient of an axial damper should be adjusted by considering the range of engine revolution, the location and vibration amplitude of the critical speed, the fore and aft vibration of the hull super structure. It needs to clarify the dynamic characteristics of the axial vibration damper to control the axial vibration appropriately. Therefore authors suggest the calculation method to analyse the dynamic characteristics of axial vibration damper. To confirm the calculation method proposed in this paper, it is applied to the propulsion shafting system of the actual ships and satisfactory results are obtained.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.520-525
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• 2011

As worldwide concern stands on global warming and greenhouse gases from internal combustion engine, the interests in technologies for a highly efficient powertrain has been increased. Concurrently the investigation to improve the deteriorated NVH, a by-product of energy efficient powertrain, is conducted seriously. The NVH performance of a new type of active engine mount that offers increased advantages over a passive hydraulic mount is examined using a newly developed 6-DOF simulator. The simulator is in the shape of Hexapod Stewart Platform adopting LEMA, a new type of actuator which is patented and commercialized by ACT Inc,, the world wide leader in the design, development, and manufacture of high performance linear electro-magnetic actuators for active vibration control. The target vibration signals of an aimed vehicle at four engine mounts are measured and simulated by 6-DOF simulator at the laboratory. The resulting NVH performances of the new active mounting system at a vehicle and on a simulator are examined and compared. Even though the active mount performance of lab test demonstrates less effective than the result of a real vehicle test, vibration reduction is identified through the simulator.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.88-94
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• 2002

For the pressurized propellant supply system of liquid rocket, feed pressure is determined with respect to the chamber pressure of normal combustion state. However, during ignition period the initial chamber pressure is atmosopheric. This may cause overflow, hard-start and even critical damage for the engine. This paper proposes an improved propellant feed system for the stable combustion of liquid rocket. The proposed system utilizes the cavitating venturi to provide stable mass flow rate. Cavitating venturi offers unique flow control capabilities at normal and abnormal combustion state, because flow rate is soley dependent on the upstream absolute pressure and fluid properties, but independent on th downstream condition. Experimental variables are propellant feed pressure and chamber pressure. The effectiveness of cavitating venturi increased when the ratio of actual feed pressure to the cavitating venturi design pressure is increased. It is also found that Kerosene if more effective to supply stable mass flow rate than LOx.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.166-174
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• 2015

This study examined combustion characteristics by selecting the fuel which have a different physical properties compared to gasoline in order to examine the effects of vehicle performance and environment depending on the physical properties. The experiment examined the combustion characteristic in the optimum ignition timing according to the physical properties change and the lean burn by performing control about ignition timing and air-fuel ratio for each fuel, and it was also evaluated the exhaust gas according to the experiment. We used a single-cylinder engine for the experiment, and tested for gasoline properties change by selecting a fake fuel that beyond the fuel quality standards in 석대법. As a result, in the case of the selected fuel showed a difference in Octane and distillation characteristics, vapor pressure and it was also found to unstable combustion, and leads to a large amount of harmful exhaust gas.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.39-45
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• 2006

In liquid rocket engine turbopump, it is difficult to evaluate turbine performance for high pressure, high temperature circumstance. Turbine test is often done by using air at similarity condition so that the turbine can be tested at lower risk. This paper describes an air similarity test program of liquid rocket engine turbopump turbine. A test facility has been built to evaluate aerodynamic performance of turbines. The test facility consists of high pressure air supply system, mass flow rate measuring nozzle, test section, hydraulic break, exit orifice for pressure control, instrumentation and control system. This paper also presents how to decide the similarity conditions of the turbine test and describes how to control test conditions. Relative standard deviation of measurement parameter was less than 1% and measured turbine efficiency corresponded with analysis result within 2%.

• Journal of Navigation and Port Research
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• v.33 no.5
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• pp.303-308
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• 2009

Recently, unmanned systems have been studied and developed in various areas including aircrafts, automobiles and vessels. In addition, many researches about unmanned systems in Korea have been studying actively with the advancement of IT However, it is not satisfied with the result of the researches and developments. Bemuse of the reason we've here tried to make a very small USV which is a barge type. We applied the Great circle navigation calculation based on GPS to the autonomous navigation algorithm and used the LabVIEW 8.2 developed by NI corp. for programming The engine and rudder were controlled by pulse width modulation method. The engine system was composed of the DC motor and ESC(Electronic Speed Controller). It was also applied by the direct cooling system using DC motor pump. A very small USV was designed and made by ourself and it was verified the effectiveness of autonomous navigation algorithm through the tests at the sea.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1121-1126
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• 2010

This study is to investigate the effects of aromatics and T90 for low cetane number (CN) fuels on combustion and exhaust emissions in low-temperature diesel combustion. We use a 1.9-L common rail direct injection diesel engine at 1500 rpm and 2.6 bar BMEP. Low temperature diesel combustion was achieved via a high external EGR rate and strategic injection control. The tested fuels four sets: the aromatic content was 20% (A20) or 45% (A45) and the T90 temperature was $270^{\circ}C$ (T270) or $340^{\circ}C$ (T340) with CN 30. Given the engine operating conditions, the T90 was the stronger factor on the ignition delay time, resulting in a longer ignition delay time for higher T90 fuels. All the fuels produced nearly zero PM because of the extension of the ignition delay time induced by the low cetane number. The aromatic content was the main factor that affected the NOx and the NOx increased with the aromatic content.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.3
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• pp.160-167
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• 2020

A two-stroke diesel engine and a propeller normally adopted in large merchant ships are regarded as major ship vibration sources. They are directly connected and generate various excitation components proportional to the rotating speed of diesel engine. Among the components, the magnitude of two excitation components with the same frequency generated by both engine and propeller can be compensated by the adjustment of their phase difference. It can be done by the optimization of propeller assembly angle but requires a number of burdensome trials to find the optimal angle. In this paper, the efficient estimation method to determine optimal propeller assembly angle is proposed. Its application requires the axial vibration measurement in sea trial and the numerical vibration analysis for propulsion shafting which can be substituted by additional vibration measurement after one-trial modification of propeller assembly angle. In order to verify the validity of the proposed method, the phase difference between two fifth order excitation components generated by both diesel engine and propeller of a real ship is calculated by the finite element analysis and its result is indirectly validated by the comparison of axial vibration responses at intermediate shaft obtained by the numerical analysis and the measurement in sea trial. Finally, it is numerically confirmed that axial vibration response at intermediate shaft at a resonant speed can be decreased more than 87 % if the optimal propeller assembly angle determined by the proposed method is applied.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.64-77
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• 2020

An electric-pump cycle, which is a propellant supply system for driving pumps of a liquid rocket engine using an electric motor, has the advantages of simple system configuration and easy control of supply flow rate and pressure. This paper investigates and analyzes the overseas research trends of the electric-pump cycle. In addition, the research and development country, performing organization, application, engine thrust, pump pressure increase, motor power, and rotation speed are summarized. Among them, the design variables of the overseas research that applied the upper-stage propulsion system with the thrust range of 0.445~2.2 kN could be used in the study of a similar electric-pump cycle in Korea.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.825-832
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• 2016

This paper describes the development of a data bus analyzer for use in avionics systems integration test. The data bus analyzer is equipped with MIL-STD-1553B, CAN and Ethernet interface cards which is incorporated in a majority of the avionics systems to accommodate a variety of interfaces. It has an individual hardware for a capture engine and a analyzing engine in order to perform the collection and the analysis of the bus data at the same time efficiently. It provides a data display function of the grid, 2-dimensional and 3-dimensional form to increase the data analysis efficiency. Verification of the data bus analyzer was carried out module unit testing and inter-module integration testing on the basis of the test procedures. Verification of interlocking requirement and usefulness of developed equipment was confirmed through an integration test result performed on a system integration laboratory of aircraft which is an actual testing environment.