• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.2
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• pp.46-54
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• 2015

Nitrous oxide is known as green and safe propellant, and can be supplied by its own vapor pressure. So, many liquid propulsion research institutes and university laboratories use nitrous oxide as oxidizer of experimental liquid rocket engine. However, the unknown explosions occurred twice during hot fire experiments using subscale ethanol/nitrous oxide thruster. In this paper, we surmised that the explosions were caused by the decomposition of nitrous oxide in the injector body and the recondensation of nitrous oxide. Improvement and the safe handling methods are suggested.

• The Journal of the Convergence on Culture Technology
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• v.6 no.1
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• pp.477-483
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• 2020

The rehabilitation methods used in existing concrete box structures rely on the method of attaching the repair material to the section of the structure with a spray equipment. In the case of ceiling or wall parts, the adhesion force to the repair material may be reduced by the gravity and dead load after construction. In subway structures, vibration causes a problem that reduces the initial adhesion. Supplementary measures are needed as the quality of repair varies depending on the worker's proficiency and construction environment. In this study, mechanical pressurization equipment was developed that can apply a certain pressure after construction of a repairwork to solve problems such as reduction of adhesion of repair materials by gravity and variation of repair quality by labor work. To find out the effect of the pressurized equipment, a chamber similar to the field conditions was constructed to measure the attachment strength different from the pressurized condition, the section, and the environmental conditions. The pressurization differed from the other parts, but the adhesion strength of up to 70% was increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.815-820
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• 2010

Fuel spray characteristics of the gasoline engine injector has been studied experimentally. Wall wetting fuel stream of the 4-hole and 12-hole injectors has been tested and measured with various installation angle and port masking shapes. Spray visualization has been performed to analyze spray formation, spray angle, and penetration length. Test result shows that wall wetting is greatly influenced by the induction air flow and injector installation angle. Wall wetting amount decreased as injector installation angle decreased. Masking decreased wall wetting amount by increasing local intake-air flow velocity due to the decreased section area. Spray visualization showed that the 12-hole injector has robust performance characteristics compared with the 4-hole injector.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.1-7
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• 2015

An ammonia fuel system is developed and applied to a 1 liter gasoline engine to use ammonia as primary fuel. Ammonia is injected separately into the intake manifold in liquid phase while gasoline is also injected as secondary fuel. As ammonia burns 1/6 time slower than gasoline, the spark ignition is needed to be advanced to have better combustion phasing. The test engine showed quite high variation in the power output to lead high increase in THC emission with large amount of ammonia, that is, higher than 0.7 ammonia-gasoline fuel ratios.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.245-245
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• 2010

최근에 반도체 소자 및 마이크로머신, 바이오센서 등에 사용되는 미세 부품에 대한 연구 개발이 활발히 진행되고 있다. 미세 부품을 제작하기 위한 MEMS 공정은 대표적으로 화학용액을 이용한 습식식각, 플라즈마를 이용한 건식식각 등이 주를 이룬다. Micro blaster는 경도가 강하고 화학적 내성을 가지며 용융점이 높아 반도체 MEMS 공정에 어려움이 있는 기판을 다양한 형태로 식각 할 수 있는 기계적인 식각 공정 기술이라 할 수 있다. Micro blaster의 식각 공정은 고속의 날카로운 입자가 공작물을 타격할 때 입자의 아래에는 고압축응력이 발생하게 되고, 이 고압축 응력에 의하여 소성변형과 탄성변형이 발생된다. 이러한 변형이 발전되어 재료의 파괴 초기값보다 크게 되면 크랙이 발생되고, 점점 더 발전하게 되면 재료의 제거가 일어나는 단계로 이루어진다. 본 연구에서는 micro blaster 장비를 반도체 MEMS 공정에 적용하기 위한 식각 특성에 관하여 확인하였다. Micro blaster 장비와 식각에 사용한 파우더는 COMCO INC. 제품을 사용하였다. Micro blaster를 $Al_2O_3$ 파우더의 입자 크기, 분사 압력, 기판의 종류, 노즐과 기판과의 간격, 반복 횟수, 노즐 이동 속도 등의 공정 조건에 따른 식각 특성에 관하여 분석하였다. 특히 실제 반도체 MEMS 공정에 적용 가능한지 여부를 확인하기 위하여 바이오 PCR-chip을 제작하였다. 먼저 glass 기판과 Si wafer 기판에서의 식각률을 비교 분석하였고, 이 식각률을 바탕으로 바이오 PCR-chip에 사용하게 될 미세 홀과 미세 채널, 그리고 미세 챔버를 형성 하였다. 패턴을 형성하기 위하여 TOK Ordyl 사의 DFR(dry film photoresist:BF-410)을 passivation 막으로 사용하였다. Micro blaster에 사용되는 파우더의 직경이 수${\mu}m$ 이상이기 때문에 $10\;{\mu}m$ 이하의 미세 채널과 미세홀을 형성하기 어려웠지만 현재 반도체 MEMS 공정 기술로 제작 연구되어지고 있는 바이오 PCR-chip을 직접 제작하여 micro blaster를 이용한 반도체 MEMS 공정 기술에 적용 가능함을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.286-286
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• 2010

최근에 환경 오염과 화석 에너지의 고갈 문제를 해결하기 위하여 태양광을 전기 에너지로 변환하는 태양전지 연구에서 가장 이슈가 되는 부분은 저가격화와 고효율이다. 상용화 되어 있는 대부분의 태양전지는 단결정 실리콘 웨이퍼와 다결정 실리콘 웨이퍼를 사용한다. 실리콘 웨이퍼의 원자재 가격을 낮추는 방법에는 한계가 있기 때문에 태양전지 제작 공정에서 공정 단가를 낮추는 방법이 많이 연구되고 있고, 실리콘 웨이퍼가 가지는 재료의 특성상 화합물을 이용한 태양전지 보다 낮은 효율을 가질 수밖에 없기 때문에 반도체 소자 공정을 응용하여 실리콘 웨이퍼 기판에서 고효율을 얻는 방법으로 연구가 진행 되고 있다. 본 연구에서는 마이크로 블라스터를 이용하여 태양전지 cell 상부에 AG(anti-glare)를 가지는 유리 기판을 형성하여 낮은 단가로 태양전지 cell의 효율을 향상시키기 위한 연구를 진행 하였다. 태양전지 cell 상부에 AG를 가지는 유리 기판을 형성하게 되면 태양의 위도가 낮아 표면에서 대부분 반사되는 태양광을 태양전지 cell에서 광기전력효과가 일어나게 하여 효율을 향상시킨다. 이때 사용한 micro blaster 공정은 고속의 입자가 재료를 타격할 때 입자의 아래에는 고압축응력이 발생하게 되고, 이 고압 축응력에 의하여 소성변형과 탄성변형이 발생된다. 이러한 변형이 발전되어 재료의 파괴 초기값보다 크게 되면 크랙이 발생되고, 점점 더 발전하게 되면 재료의 제거가 일어나는 단계로 이루어지는 기계적 건식 식각 공정 기술이라 할 수 있다. 먼저 유리 기판에 마이크로 블라스터 장비를 이용하여 AG를 형성한다. AG는 $Al_2O_3$ 파우더의 입자 크기, 분사 압력, 노즐과 기판과의 간격, 반복 횟수, 노즐 이동 속도 등의 공정 조건에 따른 유리 기판 표면에서의 광학적 특성 및 구조적 특성에 관하여 분석하였다. 일반적인 태양전지 cell 제작 공정에 따라 cell을 제작 한후 AG 유리 기판을 상부에 형성시키고 솔라시뮬레이터를 이용하여 효율을 측정하였다. 이때 솔라시뮬레이터의 광원이 고정되어 있기 때문에 태양전지 cell에 기울기를 주어 태양의 위도 변화에 대해 간접적으로 측정하였다. AG 유리 기판이 태양전지 cell 상부에 형성 되었을 때와 없을 때를 각각 비교하여 AG 유리 기판이 형성된 태양전지 cell에서의 효율 향상을 확인하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.1108-1111
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• 2009

Auto Pilot is the system which move automatically the vessel through locating operation mode to automatic after entering operating course using a electronic chart or plotter. And water jet is the a propulsion system that make a power to push the vessel through spouting the accelerated water which is absorbed by the hole in the bottom of vessel. The water jet receive the effect of the depth of water lowly, it's acceleration efficiency is higher under high speed and have an advantage on vibrating and floating sound, so it's demand is increasing as new propulsion system. However, the signal systems of auto pilot and water jet are different, we need the system to interface between each system. We designed the interface that efficiently digital feed back control embedded module between auto pilot and water jet system in this paper.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.78-84
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• 2020

The performance of pintle thruster is analyzed by using the pintle thruster performance analysis model which integrating the element models introduced in Part I. To verify the performance analysis, the results of the developed program are compared with the experimental data of kerosene/hydrogen peroxide liquid pintle thrusters. Based on the results, the characteristics of the pintle thruster are analyzed. The sensitivity analysis is performed to investigate the effect of thruster shape and operation parameters on performance characteristics using both OAT and scatter plot methods. The four performance parameters such as droplet diameter, film flow rate, O/F ratio, and nozzle throat diameter are evaluated to investigate their effects on characteristic speed, combustor pressure, and specific thrust.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.84-93
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• 2022

To implement carbon-neutrality in transportation sectors until 2050, hydrogen is considered a promising fuel for internal combustion engines because hydrogen does not contain carbon itself. Although hydrogen does not emit CO₂ emission from its combustion process, the low energy density in a volume unit hinders the adoption of hydrogen. Therefore, the understanding of hydrogen jet behavior and measurement of equivalence ratio must be conducted to completely implement the high-pressure hydrogen direct injection. The main objective of this research is feasibility test of hydrogen local equivalence ratio measurement by laser-induced breakdown spectroscopy (LIBs). To visualize the macroscopic structure of hydrogen jet, high-speed schlieren imaging was conducted. Moreover, LIBs has been adopted to validate the feasibility of hydrogen local equivalence ratio measurement. The hydrogen injection pressure was varied from 4 MPa to 8 MPa and injected in a constant volume chamber where the ambient pressure was 0.5 MPa. The increased injection pressure extends the vertical penetration of hydrogen jet. Due to the higher momentum supply when the injection pressure is high, the hydrogen has easily diffused in all directions. As the laser trigger timing has delayed, the low hydrogen atomic emission was detected due to the longer mixture formation time. Based on equivalence ratio measurement results, LIBs could be applied as a methodology for hydrogen local equivalence ratio measurement.

• Journal of Soil and Groundwater Environment
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• v.13 no.5
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• pp.81-87
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• 2008

In accompany with the transfer of US army bases, recent surveys reported serious contamination of soils by the release of petroleum from storage facilities and heavy metals accumulated in rifle-ranges. These problems have made an increased concerns of cleanup technology for contaminated soils. In this study, a full-scale soil washing process improved by multistage continuous desorption and agitational desorption techniques was examined for petroleum-contaminated soils obtained from three different remedial sites that contained 29.3, 16.6, and 7.8% of silt and clay, respectively. The initial concentrations of total petroleum hydrocarbon (TPH) were 5,183, 2,560, and 4,860 mg/kg for each soil. Pure water was applied to operate washing process, in which water used for washing process was recycled 100% for over 6 months. The results of full-scale washing tests showed that the TPH concentrations for soils (> 3.0 mm) were 50${\sim}$356 mg/kg (85.2${\sim}$98.2% removal rates), regardless of the contents of silt and clay from in A, B and C soil, when the soils were washed at 3.0 kg/$cm^2$ of injection pressure with the method of wet particle separation. Based on the initial TPH concentration, the TPH removal rates for each site were 85.2, 98.2 and 89.9%. For soils in the range of 3.0${\sim}$0.075 mm, the application of first-stage desorption technique as a physical method resulted 834, 1,110, and 1,460 mg/kg of TPH concentrations for each soil, also additional multi-stage continuous desorption reduced the TPH concentration to 330, 385, and 245 mg/kg that were equivalent to 92.4, 90.6, and 90.1% removal rates, respectively. The result of multi-stage continuous desorption for fine soil (0.075${\sim}$0.053 mm) were 791, 885, and 1,560 mg/kg, and additional agitation desorption showed 428, 440, and, 358 mg/kg of TPH concentrations. Compared with initial concentration, the removal rates were 92.0, 93.9 and 92.9%, respectively. These results implied we could apply strategic process of soil washing for varies types of contaminated soils to meet the regulatory limit of TPH.