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The fatigue strength of the high strength steel sheet for truck frame use was investigated. The fatigue strength of the steel sheet with scale increases with the decrease in the roughness of the steel sheet surface. The fatigue strength of the sheared edge increases with the decrease in the roughness of the fractured surface. In case of the microstructure consisting of pearlite and coarse carbides, the fatigue strength of the sheared edge decreases. Based on these findings, two types of the 780MPa grade high strength hot rolled steel sheet with high fatigue strength as well as good formability have been developed.

Since in-cylinder flame temperature has a direct effect on an engine's NOx characteristics, these phenomena have been studied in detail in a DI diesel engine using a newly developed method allowing the in-cylinder temperature distribution to be measured by the two color method. The flame light introduced from the visualized combustion chamber of the engine is divided into two colors by filters. The images of combustion phenomena using the two wavelengths are recorded with a framing streak camera which includes a CCD camera. The flame temperature is immediately calculated by a computer using two color images from the CCD camera. A parameter study was then carried out to determine the influence of intake valve number of the engine, and fuel injection rate (pilot injection) on the in-cylinder temperature distribution.

Direct and Schlieren Photographing of the combustion process in an actual D.I. diesel engine have been investigated, and by comparing both direct and schlieren methods with cylinder pressure measurement, the characteristics of mixing, ignition and burning process were analyzed. The different combustion characteristics induced by various in-cylinder air motions were also observed. The injected fuel spray jet pattern, which impinged on the combustion chamber wall, seems to affect the mixing process due to combination with in-cylinder air motion. The development of fuel jet spray was observed and compared with some theoretical treatments. The contribution of turbulence on combustion both in pre-mixed and diffusion type burning period was recognized and the effect of swirl especially on diffusion burning period was also confirmed.