This paper describes the measurement of in-cylinder engine friction using the instantaneous IMEP method. This method has been applied to measure in-cylinder friction force in a modern, low friction design production spark ignited engine. An improved mechanical telemetry system has been developed to implement this method. The telemetry system continues to provide excellent data even after 50+ hours of operation at speeds as high as 2000 rpm.

Investigated in this study were the primary sources of error associated with this technique. Also presented are the steps taken to minimize the effects of these errors. The refined technique has been subsequently used to obtain piston assembly friction data for both motoring and a limited number of firing cases. The effects of design parameters and operating conditions were investigated. In addition, crank-angle resolved and cycle-integrated results, converted to in-cylinder FMEP, were compared and the trends obtained were consistent with the Stribeck curve. The ratio of in-cylinder to total engine FMEP ranged from 19-45% in the tests performed in this study.

This technique was also used to obtain “cold-start” incylinder friction data, which in turn were used to calculate an oil viscosity correction coefficient. This coefficient was implemented in an engine friction model for prediction of motoring and firing friction at different operating temperatures.