Dept of Mech Eng and Appl Mech University of Michigan

OVER THE YEARS it has come to be recognized that piston and ring assembly friction is the primary source of friction in the reciprocating diesel engine. Under part-load operation and moderate speeds, piston and ring friction may account for up to 60% of engine friction. In a minimally cooled or adiabatic diesel, piston and ring friction could become excessively high, and in fact could negate much or all of the efficiency benefits of reduced heat rejection. Unlike the friction of some other components of the engine, the measurement of piston and ring friction is very difficult. No satisfactory bench tests have been developed which simulate the complex thermal and mechanical environment of the operating engine.

A review of the literature shows that several researchers have reported measurement of piston and ring friction. Pioneering work was done by Forbes and Taylor (1) at MIT in the 1940's. In that study the bore was elastically mounted so that the friction forces between the rings and the liner caused deflections of the bore. These were recorded optically and related to friction. More recently Furuhama et. al. (2,3) have developed a moveable bore method for use on both diesel and gasoline engines. Typically moveable bore methods require extensive engine modifications.

The present paper discusses two approaches that are being used at the University of Michigan on the Cummins 903 engine. The first is termed the Instantaneous IMEP method (4,5,6) and is now well developed. The second is a new method termed the Fixed Sleeve method, and is a derivative of the moveable bore method typified by Taylor and Furuhama.

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