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Recent literature published by Toyota Motor Company[1] and Musashi Institute of Technology[2] have found that an offset crankshaft design has the potential for reducing friction and possibly increasing thermodynamic efficiency. In an effort to further evaluate this potential, a single-cylinder variant of a production GM 4.2L I6 engine was designed and tested. Cylinder pressure acquisition equipment and dynamometer torque measurements were used to quantify differences in combustion performance and firing friction between an offset crankshaft design and a standard baseline configuration. Extensive testing on the single-cylinder engine in both configurations found no significant frictional or thermodynamic differences to exist. Multiple tests of both design configurations were run in an effort to increase statistical confidence and test data showed good repeatability and precision.

Comparisons are made between friction predictions of the FLARE (Friction and Lubrication Analysis of Reciprocating Engines) computer code and experimental data for the purpose of validating FLARE. An in-line four-cylinder engine under motoring conditions was selected for doing the experiments. Three major friction producing subassemblies were considered: piston assembly, crankshaft main bearings, and valve train. A Taguchi-type L16 matrix was used for the piston assembly, while an L8 matrix was used for the valve train. A traditional approach (varying one parameter at a time) was used for crankshaft main bearings. The agreement between experimental measurements and FLARE predictions, for all the cases studied, is very good. The match is closest for the valve train, followed by the crankshaft main bearings and piston assembly. In addition, trends and effects of changing design parameters are predicted correctly by FLARE.