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Lean-burn technology is now being reviewed again in view of demands for higher efficiency and cleanness in internal combustion engines. The improvement of combustion using in-cylinder gas flow control is the fundamental technology for establishing lean-burn technology, but the great increase in main combustion velocity due to intensifying of turbulence causes a deterioration in performance such as increase in heat loss and N0x. Thus, it is desirable to improve combustion stability while suppressing the increase in main burn velocity as much as possible (1). It is expected that the fluid characteristics of the in-cylinder tumbling motion that the generated vortices during intake stroke breake down in end-half of compression stroke will satisfy the above requisition. This study is concerned with the effects of enhancing of tumble intensity on combustion in 4-valve S. I. engines.

Recent years have seen much effort being expended to increase engine output while reducing engine volume, to achieve better fuel economy. In increasing engine output, the lubricating conditions of engine sliding areas come to be strict. It becomes important, therefore, to define the critical values of lubrication for ensuring engine reliability. In these aspects, a new method to measure piston temperature of the reciprocating engine was developed. This method employs a torsion coil spring as contact which sends out signals of piston temperatures. This contact has superior response and durability and being compact, makes it possible to take multi-channel measurement. In addition, it is demonstrated that this method for measuring sliding surface temperature permits evaluation of durability with con rod big end bearing and piston lateral face in a short time.