Recently, the automobile industry has focused on the FIE system of diesel engine with common-rail, EGR, and turbo charger in order to meet a more stringent emission and fuel economy regulations. High-pressure fuel direct injection by using common-rail system is widely accepted because diesel combustion and emission characteristics highly depend on the formation of air-fuel mixture quality. By this fact, an electro-hydraulic injector for common-rail fuel injection system should be designed to have precise and fast response of injector needle's opening and closing behavior to enhance air-fuel mixing rate. As know, most electro-hydraulic injectors provide its nozzle movement by solenoid coil energy or piezo-actuation. Relatively, servo-hydraulic type piezo injector with bypass-circuit mechanism, which it serve to amplify extension of the piezo stack, is also known for their good efficiency. So the piezo actuator triggers pilot valve for controlling pressure balance, which is accurately regulated by bypass-circuit system. Therefore, main actuation force of piezo injector to move injector needle is hydraulic, which is the key object as it is aimed towards all this research ranges: numerical and experimental approaches. In this study, firstly a full-circuit numerical model of an indirect acting piezo injector with bypass-circuit by using AMESim code has been developed to predict dynamic characteristics of hydraulic components and verified by comparison with experimental data. Also, two experiment schemes were carried out using a constant volume chamber with LED back-illumination system for Mie scattering and a single-cylinder CR direct-injection engine, equipped with a bypass-circuit type piezo and solenoid injector to compare high-speed spray and combustion characteristics in this study because spray penetration and duration are key factor in diesel diffusion combustion. As main results obtained by this study, the injection flow rate and injector internal pressure dynamics calculated by AMESim environment of a bypass type piezo-driven injector reasonably agreed with the experimental result. Also it has better capability in controlling injector needle closing delay and a beneficial effect on diesel diffusion combustion.

Although the sliding friction of patterned surfaces on ice has been investigated for over a century, physical analysis still needs to be improved. In this study, we investigate the friction coefficient on ice by changing the experimental conditions of temperature, gap between line patterns (20 μm and 200 μm), and sliding direction. In the temperature region of −17.7 °C < T <−2.5 °C, a longer gap (200 μm) patterned surface has a lower friction coefficient for both parallel and perpendicular sliding directions at the same temperatures. Interestingly, a lower friction coefficient is found when the sliding direction is perpendicular to the micro-structure patterns at T < −7.6 °C for gap = 20 μm and at T < −9.9 °C for gap = 200 μm. To understand this interesting phenomenon, a theoretical model is derived by modifying the model from the study by Oksanen and Keinonen. Based on this modified model, the surface with a shorter gap (20 μm) makes fewer contacts and the pattern direction determines the water layer elongation at each contact. This validates that friction on ice can be controlled using a micro-structure pattern and moreover suggests a method for finding an optimized micro-structured surface for reducing friction on ice.

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Miller cycle(밀러 사이클), Atkinson cycle(앳트킨슨 사이클), In-cylinder flow(실린더 내 유동), Variable valve timing(가변밸브 개폐시기), Intake valve closing angle(흡기밸브 닫힘각), ANSYS simulation(ANSYS 해석), Moving mesh(이동 격자)

Recently, R&D demand for environmental friendly vehicle has rapidly increased due to its global environmental issues such as global warming, energy and economic crisis. Under this situation, the most realistic alternative way for environmental friendly vehicle is a clean diesel vehicle. The common-rail fuel injection system, as key technology of clean diesel vehicle, consists of a high pressure pump, common-rail, high pressure fuel line and electronic control injector. In common-rail highpressure fuel injection system, high pressure wave of injection system and geometry of injector elements have a major effects on high-pressure fuel spray. Therefore, in this study, the numerical model was developed for analysis about the common-rail fuel pressure pulsation by using AMESim code. We could secure stability of common-rail high-pressure fuel injection system through optimal design of fuel line. . 서 론최근 커먼레일 연료 분사시스템은 크게 고압펌프, 커먼레