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In accordance with the rising concern about global environmental protection, exhaust emissions regulations for industrial diesel engines are also being strengthened worldwide in stages. In order to comply with the EPA Tier3 and interim Tier4 level, EGR (Exhaust Gas Recirculation) system is recognized as one of the most potential technologies to reduce Nitrogen Oxide (NOx), but there were concerns about durability deriving from the fuel quality and cost increase from additional parts like as EGR cooler, reed valve and EGR valve. To overcome these problems and to fulfill the market demands for industrial diesel engines, such as low cost, compactness, high output and high durability, most appropriate system should be chosen for each engine type.

Optimization of combustion system is important element to design reciprocating engines and Computational Fluid Dynamics (CFD) approach is an effective tool for it. Though CFD approach is widely used to analyze air motion now, further improvement is needed for fuel spray applications especially practical use, such as requirement of special knowledge and its complicated behavior. In this thesis, CFD approach was applied to the free spray in the test rig to understand the diesel spray characteristics and applicability for practical design. A spray visualization techniques including Phase Doppler Particle Analyzer (PDPA) were combined for further understanding. As a result, fuel injection systems were evaluated by CFD approach, that showed the potential to use for practical design process.

Lately, numerical approach plays an important role in developing reciprocating engines due to the requirement of both higher performance and environmental protection, such as exhaust emission. Using numerical approach, the performance of each engine parts can be predicted before testing and some behavior which are difficult to be visualized directly can be understood. Especially, the engines in this paper have their particular characteristics to be solved. Evaluation of In-Direct Injection system (IDI) is key issue to improve exhaust emissions. Their small dimensions also cause some difficulties to design and development. In this paper, some numerical approaches including Computer Fluid Dynamics were used to solve these tasks. In the end, we could introduce the new small IDI diesel engines with high performance, low exhaust gas emissions and good NVH characteristics.

In designing new valve train system, it is useful to predict the complicated dynamic characteristics correctly by CAE simulation at the initial stage. In this paper, a modeling technique of mechanical system simulation and the simulation results about the dynamic characteristics of the diesel engine valve train are shown. From the measured results, it is found that the valve spring plays an important role in the dynamic characteristics of valve train. Based on the results, we propose a new model which use beam coupled the displacement and shearing stress and gap elements to express the valve spring. The model is proved very well to express not only the same-pitch valve spring but also the different-pitch valve spring. As a result, the prediction of the dynamic characteristics of the valve train provides a lot of effective data and hint for the developing valve train design of a newly designed diesel engine.

The simulation techniques play important role on contemporary engine design. In this study, computer fluid dynamics approach (CFD) was focused to design the intake and combustion system of the direct injection diesel engine for versatile use. A practicality was stressed as much as an accuracy to correspond to designer and researcher's requirements, such as close relationship to the engine performance and short period of computation. The correlation of the trapping efficiency and the swirl ratio was mainly focused. A steady flow rig tests and engine operation data were combined to improve their quality mutually.