• 한국분무공학회지
• /
• 제25권2호
• /
• pp.60-67
• /
• 2020

Despite its benefit in engine thermal efficiency, gasoline-direct-injection (GDI) engines generate substantial particulate matter (PM) emissions compared to conventional port-fuel-injection (PFI) engines. One of the reasons for this is that the spray collapse caused by the spray-to-spray interaction forms the locally rich fuel-air mixture and increases the fuel wall film. Previous studies have investigated the spray collapse phenomenon through the macroscopic observation of spray behavior using laser optical techniques, but it is somewhat difficult to understand the interaction between sprays that is initiated in the near-nozzle region within 10 mm from the nozzle exit. In this study, the spray structure, droplet size and velocity data were obtained using an X-ray imaging technique from the near-nozzle to the downstream of the spray to investigate the spray-to-spray interaction and discuss the effects of spray collapse on local droplet size and velocity distribution. It was found that as the ambient density increases, the spray collapse was promoted due to the intensified spray-to-spray interaction, thereby increasing the local droplet size and velocity from the near-nozzle region as a result of droplet collision/coalescence.

• Computers and Concrete
• /
• 제20권5호
• /
• pp.617-625
• /
• 2017

Prestress force identification (PFI) is crucial to maintain the safety of prestressed concrete bridges. A synergic identification method has been proposed recently by the authors that can determine the prestress force (PF) and the excitation force simultaneously in prestressed concrete beams with good accuracy. In this paper, the ability of this method in the application with prestressed concrete box-girder bridges is demonstrated. A reasonable assumption is made to capture the similarity of the dynamic behavior of the prestressed concrete box-girder bridge and a beam under a certain loading scenario, and the feasibility of this method for application in a prestressed box-girder bridge is affirmed. A comprehensive laboratory test program is conducted, and the effects of PF, excitation, measuring time and uncertainties are studied. Results show that the proposed method can predict the PF and the excitation force in a prestressed concrete box-girder accurately and has a great robustness against uncertainties.

• 한국건축시공학회지
• /
• 제13권2호
• /
• pp.112-121
• /
• 2013

Korean overseas construction has been on the rise, and exceeded the 2011 goal of $50 billion by securing $59.1 billion in orders. However, these orders were heavily concentrated in the Middle East (50%) and plant construction contracts (75%). This study suggests that, to maintain growth in foreign markets, Korea construction companies should enter into the high value-added investment development business and aggressively seek ways to diversify their regions of activity and construction types. To secure the entry of Korean construction companies into lucrative markets and better understand the competitive factors facing Korean construction concerns, a survey of the literature and focus group discussions targeting relevant experts were carried out. From those efforts, a list of 44 competitive factors crucial to entering and competing in the international investment development business was developed. Survey responses were analyzed by applying IPA. The results revealed that while Korean concerns compete well in engineering/technical capabilities, maintaining a cooperative relationship with contractors, and warranty/after sales service capabilities, their ability to obtain business information on the target country, to form private/public cooperative systems, and to build international human networks require immediate improvement.

• 한국분무공학회지
• /
• 제14권4호
• /
• pp.184-189
• /
• 2009

Recently, ultrafine particles emitted from internal combustion engine is main concern because of its well known adverse health effects. So Europe decided to start the regulation about diesel engine particle number emissions. The nanoparticles smaller than 50nm in diameter have the ability to penetrate deep into interstitial tissue of luge, where they may cause severe respiratory inflammation and acute pulmonary toxicity. Recent studies have showed that spark ignition engines emit particles number concentration comparable to those from diesel engines with DPF under high load and rich mixture conditions, including cold starts and acceleration. So this study investigated emission characteristics of ultrafine particles according to fuel injection type in gasoline vehicles and LPG vehicles. The test vehicles were tested on CVS-75 and NEDC vehicle test mode using the chassis dynamometer, CPC system applied as a particle measuring instrument at the end of dilution tunnel. As a result, the correlation between fuel injection type and particulate emission was determined. GDI vehicle emitted 10 times higher particles than PFI vehicles, and compared to Mixer and LPGI type LPG vehicle, LPLI vehicle emitted particles high.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2008년도 정기학술발표대회 논문집
• /
• pp.38-43
• /
• 2008

한 국가의 SOC 시설 보유량은 공공서비스의 공급능력을 보여주는 지표로 활용되고 있으며, 국가경쟁력의 원천이 되고 있다. 한국은 SOC 시설이 충분하다는 판단하에 '03년 이후 SOC 투자를 점차 축소하고 있다. 하지만 SOC 투자 축소는 기존 SOC 공사의 공기지연이 발생하고 있으며, 향후에는 국가경쟁력을 저해할 가능성을 갖고 있다. 따라서 충분한 수준의 SOC 투자는 지속되어야 한다. 이를 위해 우선 교통시설특별회계를 최소한 국가기간교통망계획의 계획기간인 '19년까지 연장할 필요가 있다. 또한 민간투자사업을 효과적으로 활용하고, SOC 투자를 완공위주의 집중투자를 해야 한다.

• 한국분무공학회지
• /
• 제22권1호
• /
• pp.1-7
• /
• 2017

Recently, Performance and fuel efficiency of gasoline engines have been improved by adopting direct injection (DI) system instead of port fuel injection (PFI) system. However, injecting gasoline fuel directly into the cylinder significantly reduces the time available for mixing and evaporation. Consequently, particulate matters(PM) emissions increase. Moreover, as the emission regulations are getting more stringent, not only the mass but also the total number of PM should be reduced to satisfy the Euro VI regulations. Increasing the fuel injection pressure is one of the methods to meet this challenge. In this study, the effects of increased fuel injection pressures on combustion and emission characteristics were experimentally examined at several part load conditions in a 1.6 liter commercial gasoline direct injection engine. The main combustion durations decreased about $2{\sim}3^{\circ}$ in crank angle base by increasing the fuel injection pressure due to enhanced air-fuel mixing characteristics. The exhaust emissions and number concentration distributions of PM with particle sizes were also compared. Due to enhanced combustion characteristics, THC emissions decreased, whereas NOx emissions increased. Also, the number concentrations of PM, larger than 10 nm, also significantly decreased.

• 국제학술발표논문집
• /
• The 6th International Conference on Construction Engineering and Project Management
• /
• pp.32-36
• /
• 2015

This study explores the issue of program management consortia involving multinational participants. The aim of this research was to leverage advantages in program management (PM) skills and PM model improvement in product line construction in mega scale construction programs, typically funded by public funds. Such ventures involve multinational parties using dedicated partnering based on a program management consortium (PMC) to reduce confrontation between parties in complex circumstances, allowing an open and non-adversarial approach to project management. This research also seeks to implement an ongoing feedback program of best practices and lessons learned to minimize the repetition of mistakes and to reduce costs in sequenced construction. Recently, the Korean government has planned to undertake three large new projects: the Korean Peninsula major river maintenance, the reclamation of Se-Mangum, and the Science/Business City. This paper starts by providing a framework for the cost-reduction strategy for the United States Forces Korea (USFK) Relocation Program, which will be funded with public funds and a private fund investment (PFI) that combines programs executed by two governments as owners and multinational stakeholders, joined in the PMC. The establishment of project-oriented consortia is an innovative and non-adversarial approach to massive international construction projects. Such projects have used various tools effectively and skillfully. This experience may offer an opportunity to practice new and advanced program management delivery methods, and it is expected that Korea will gain a competitive advantage in the international construction market.

• 한국수소및신에너지학회논문집
• /
• 제25권6호
• /
• pp.636-642
• /
• 2014

As environment problem became a worldwide issue, countries are tightening regulations regarding greenhouse gas reduction and improvement of air pollution problems. With these circumstances, one of the renewable energies produced from biomass is getting attention. Bio-ethanol, which is applicable to SI engine, showed a positive effect on the PFI (Port Fuel Injection) type. However, Ethanol has a problem in homogeneous mixture formation because it has high latent heat of vaporization characteristics and in the GDI (Gasoline Direct Injection) type, mixture formation is required quickly after fuel injection. Particularly, South Korea is one of the countries with great temperature variation among seasons. With this reason, South Korea supply fuel additive for smooth engine operation during winter. Therefore, experimental study and investigation about application possibility of blending fuel is necessary. This paper demonstrates the spray characteristics by using the CVC direct injection and setting the bio-ethanol blending fuel temperature close to the temperature during each seasons: -7, 25, $35^{\circ}C$. The diameter and the width of the CVC are 86mm and 39mm. High-pressure fuel supply system was used for target injection pressure. High-speed camera was used for spray visualization. The experiment was conducted by setting the injection pressure and ambient pressure according to each temperature of bio-ethanol blending fuel as a parameter. The result of spray visualization experiment demonstrates that as the temperature of the fuel is lower, the atomization quality is lower, and this increase spray penetration and make mixture formation difficult. Injection strategy according to fuel temperature and bio-ethanol blending rate is needed for improving characteristics.

• 대한기계학회논문집B
• /
• 제36권3호
• /
• pp.335-342
• /
• 2012

자동차배출가스는 이산화탄소($CO_2$)에 의한 지구온난화 및 탄화수소(HC)와 질소산화물($NO_x$)에 의한 오존 생성을 야기하는 등, 인체와 환경에 나쁜 영향을 미치기 때문에 이에 대한 관심이 증폭되고 있다. 가솔린 직접분사 (Gasoline Direct Injection; GDI)엔진은 디젤엔진과 같이 연소실내에 연료를 직접 공급하는 방식으로서 가솔린엔진의 취약점으로 지적되어 오던 높은 연료소비율 문제를 획기적으로 개선할 수 있는 기술로 평가되고 있다. 본 연구에서는 분무유도방식(Spray-guided type)의 GDI엔진을 이용하여 공기과잉률 2.0 이상의 초희박 연소를 통해 연료소비율을 개선하였다. 추가적인 연료소비율 개선 및 배출가스 저감을 위해 희박연소시 다단 분사전략과 Exhaust Gas Recirculation (EGR)을 적용하였다. 배출가스 수준과 운전성능을 평가하고 이를 배출가스 규제와 비교 검토함으로써 국내 관련기술 개발 방향 및 상용화 가능성에 대해 검토하고자 하였다.

• 한국산학기술학회논문지
• /
• 제10권10호
• /
• pp.2907-2916
• /
• 2009

민간투자사업은 1990년대 이후 본격화되어 주요 교통시설을 중심으로 진행되어 왔으며 2005년 이후에는 장기간 서비스를 제공하고 임대료 방식으로 사업자에게 대가를 지급하는 BTL 방식의 사업이 도입되어 학교, 군 주거시설, 하수관거 등 다양한 분야의 시설 및 서비스가 제공되고 있다. 정부 재정사업과 차별화되는 민자사업에 대해서 관련된 위험을 도출하고 그 가치를 평가, 위험 발생을 최소화하려는 제도적 노력은 부진한 편이며 특히 장기간 서비스 계약을 통해 이루어지는 BTL 사업의 경우 위험가치 평가 제도의 도입이 시급한 실정이다. 본 연구는 민자사업 성공의 주요 원인으로 알려진 영국 등의 민자사업 위험가치 평가제도를 비교 분석하고 국내 BTL 사업의 실제 사례에 대해 위험가치를 반영한 PSC(Public Sector Comparator)를 구축, 분석하였다.