Experimental Evaluation of Piston-Assembly Friction Under Motored and Fired Conditions in a Gasoline Engine

Piston-assembly friction measurement has been carried out on a single-cylinder gasoline engine using the IMEP (indicated mean effective pressure) method at realistic engine speeds and loads without any major engine modifications. Instantaneous and mean piston-assembly friction were measured under motored and fired conditions at different lubricant temperatures. The forces acting on the piston assembly were carefully determined by measuring the cylinder pressure, crankshaft angular velocity, and strain in the connecting rod. The difference between the resulting gas pressure, inertia, and connecting rod axial forces acting on the piston yields the piston-assembly friction. To achieve this with confidence, an advanced instrumentation, telemetry, and data acquisition system was designed and developed, giving special attention to the synchronization and simultaneous sampling of analog and digital channels. Experiments are reported for piston-assembly friction at a range of engine operating conditions with different lubricant formulations, with and without a friction modifier.