• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.15-21
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• 2021

Electrically powered airplanes can reduce CO₂ emissions from fossil fuel use and reduce airplane costs in the long run through efficient energy use. For this reason, advanced aviation countries such as the United States and the European Union are leading the development of innovative technologies to implement the full-electric airplane in the future. Currently, the research and development to convert existing two-seater engine airplanes to electric-powered airplanes are underway domestically. The airplane converted to electric propulsion is the KLA-100, which aims to carry out a 30-minute flight test with a battery pack installed using the engine mounting space and copilot space. The lithium-ion battery installed on the airplane converted to electric propulsion was designed with a specific power of 150Wh/kg, weight of 200kg, and a C-rate 3~4. This study confirmed the possibility of a 30-minute flight with a designed battery pack before conducting a flight test of a modified electrically propelled airplane. The battery performance was verified by dividing the 30-minute flight profile into start/run stage, take-off stage, climbing stage, cruise stage, descending stage, and landing/run stage. The final target of the 30-minute flight was evaluated by calculating the battery capacity required for each stage. Furthermore, the flight performance of the electrically propelled airplane was determined by calculating the flight availability time and navigation distance according to the flight speed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.5
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• pp.445-455
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• 2010

In order to effectively predict thermo-acoustic instability within real combustors of rocket engines and gas turbines, in the present study, the Helmholtz equation in conjunction with the time lag hypothesis is discretized by the finite element method on three-dimensional hybrid unstructured mesh. Numerical nonlinearity caused by the combustion response term is linearized by an iterative method, and the large-scale eigenvalue problem is solved by the Arnoldi method available in the ARPACK. As a consequence, the final solution of complex valued eigenfrequency and acoustic pressure field can be interpreted as resonant frequency, growth rate, and modal shape for acoustic modes of interest. The predictive capabilities of the present method have been validated against two academic problems with complex impedance boundary and premixed flame, as well as an ambient acoustic test for liquid rocket combustion chamber with/without baffle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.417-422
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• 2010

Low temperature diesel combustion was achieved via a combination of late injection timing ($8.5^{\circ}$ CA BTDC to $0.5^{\circ}$ CA BTDC) and heavy exhaust gas recirculation (37% to 48%) with ultra low sulfur Swedish diesel fuel in a 1.7L common rail direct injection diesel engine. When injection timing is retarded at a certain exhaust gas recirculation rate, the particulate matter and nitrogen oxides decease simultaneously, while the hydrocarbon and carbon monoxide increase. Hydrocarbon speciation by gas chromatography using a flame ionization detector reveals that the ratio of partially burned hydrocarbon, i.e., mainly alkenes increase as the injection timing is retarded and exhaust gas recirculation is increased. The two most abundant hydrocarbon species are ethene which is a representative species of partially burned hydrocarbons, and n-undecane, which is a representative species of unburned hydrocarbons. They may be used as surrogate hydrocarbon species for performing a bench flow reactor test for catalyst development.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.645-649
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• 2010

Induction hardening has been used to improve the torsional strength and characteristics of wear for axle shaft that is used to transmit driving torque from the differential to the wheel in automobiles. After the rapid heating and cooling processes of induction hardening are carried out, the shaft has residual stress and material properties change; this affects the allowable transmitted torque. The objective of this study is to predict the distribution of residual stress and estimate the torsional strength of induction-hardened axle shafts with residual stress. In this study, the finite element method is used to study the thermomechanical behavior of the material, and the results are compared with experimental results. The results indicate that the torsional strength of the axle shaft depends on the surface hardening depth and distribution of residual stress.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.3
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• pp.50-57
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• 2009

A gas mechanical pulsator is developed for the study of combustion instabilities in various combustors such as LRE combustor. First, it shows that the mass flow rates and the perturbation frequencies can be successively controlled by the inlet pressure and the rotating speed of a rotating disk with many holes. Second, the device is used as an acoustic amplification source as a substitute for the speaker in the previous acoustic tests and its results show almost the same resonant frequency and damping characteristics compared with the previous results. In conclusion, the result shows that it can be used as a substitute for a speaker in the studies of LRE combustion instabilities, which has a flow and no limitation of amplification, and a device for making a perturbation source in gas flow.

• Tribology and Lubricants
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• v.28 no.4
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• pp.167-172
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• 2012

The turbo pump of a liquid rocket engine is composed of three main parts: the oxidizer pump, fuel pump, and turbine. Liquid oxygen ($LO_X$) is the working fluid in the cryogenic environment in the oxidizer pump, but tests are usually performed using liquid nitrogen ($LN_2$), which has a boiling point similar to that of $LO_X$ but is comparatively safer and easier to use for the test. In this study, a bearing test rig is developed and its performance is evaluated using a cryogenic ball bearing with $LN_2$ as the working fluid. Verifying the performance of the bearing test rig is crucial for ensuring correct working of the turbo pump unit in the liquid rocket engine. A stable test rig for the bearing in a cryogenic environment makes the bearing technology enhance its reliability. The test results show that the system operates stably and the requirement of performance time of 500 s is met. The test results of temperature, motor speed, and torque are discussed. The developed cryogenic bearing test rig is expected to help in widening knowledge and expanding research on ball bearings in the future.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.83-87
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• 1998

To reduce the supersonic jet noise from the liquid rocket engine, water injetion silencers were designed and tested. Test variables were the mass flow rate of water jet, the length of primary pipe and the diameter of expansion pipe. Followings are the results of this study. 1. From the same mass flow rate of water, longer primary pipe was more effective to reduce the noise. 2. Noise level was significantly reduced with increasingly water flow rate. 3. The optimum water flow rate was 10～12 times of the propellant flow rate. 4. By installing expansion pipe, noise level was reduced approximately 30㏈ compared to without expansion pipe

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.12
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• pp.1035-1042
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• 2016

By using commercial flight simulation game engine, X-Plane, we have studied QTG(Qualification Test Guide) generation that can satisfy FTD level 5. Flight model is SR-20 of Cirrus. In list of QTG, There are some items to measure control forces. therefore, we have installed CLS(Control Loading System) to flight control devices in order to make it possible to measure control forces. We made Autopilot function externally to make flight model in trim conditions because X-Plane don't provide internal trim routine function. In addition to develop an algorithm, it can automatically perform the test. To avoid the inconvenience to control as it was to be carried out in same conditions. In case of FTD level 5, it is possible to use alternative data sources not only real flight data. By using these alternative data sources, all test results satisfy a scope given by CFR Part 60.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.210-216
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• 2017

Recovery of low level nitric acid and sulfuric acid ions, which were contained in wastewater of a wet scrubber for de-NOx and de-SOx from ship engines, was attempted as fertilizing materials. This study utilized a selective extraction method using four organic solvents to precipitate the solid salts of ammonium nitrate and ammonium sulfate. The IR analysis showed almost same composition of the extracted ammonium salts with a commercial product, and recovery rate of nitrogen and sulfuric ions was 89% and 80% respectively. It was found that the selectivity and solubility consequently could be the crucial factors to recover the low level ions from the waste scrubbing water.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1108-1115
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• 2015

In this study, correlation equations were arranged about mass flow rates of oxygen and volume flow rates of helium using a mouthpiece method. The mouthpiece method can reduce examination cost by using similar empirical formula. Instead of liquid oxygen, in the mouthpiece method, gas helium can be measured in order to determine the leakage amount of liquid oxygen conveniently. Experiment was conducted and compared to understand leakage amount relation between the helium and the oxygen for prototype item under a room and a cryogenic temperature conditions. The leakage volume flow rate [$A.m{\ell}/s$] of the helium was 174 times higher than mass flow rate [g/s] of the oxygen leakage at liquid state. The derived correlation equations were verified using data from the National Institute of Standards and Technology (NIST).