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In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (high power density) and to have the performance to comply with stringent exhaust emissions standards as well. To meet these social demands and market requirements, there are various engineering tasks yet to accomplish. In this paper, two important technical issues have been focused, those are, combustion system improvement to enable lower exhaust emissions and higher power output than conventional models and new cooling system as a solution for increased heat load issue accompanying the progress of high power density. Firstly, for combustion system improvement, the swirl adjustment technique has been developed that will optimize the swirl ratio for each engine application with different load and speed condition.

The 82-Stroke DI (direct injection) engine has been under development at Kubota for years. Production was started in March, 1983 for installation in Kubota tractors as its first application and the cumulative production reached about 120,000 units by the end of 1986. With this performance, as a background, the launching of this DI engine into the general industrial engine market is scheduled for 1987. This new engine series is the DI version of Kubota 82-Stroke IDI (indirect injection) engine series which has reached a cumulative production of about 700 thousand units. As such, the new engine series has the dependability of the use-tested basic engine construction plus the additional features of “excellent torque characteristic”, “low fuel consumption”, “good starting characteristic” and “oil maintenance reduced to a half”.

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.

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.