An improved technique for measuring piston-assembly friction and comparative analysis with numerical simulations: Under motored condition

Robust and accurate measurement techniques are essential to studying the piston-assembly friction of Internal Combustion (IC) engines. Based on the instantaneous Indicated Mean Effective Pressure (IMEP) method, this paper develops an improved measurement technique to evaluate the piston-assembly friction in engines. Wireless telemetry technology is employed in the measurement of connecting rod axial force, which greatly minimizes the engine modifications and enhances the measurement stability compared to the conventional wired way. The measurement system, which is composed of computer, data acquisition system, sampling trigger apparatus and sensors, is exploited with special attention given to the sampling synchronization of signal channels including cylinder pressure, connecting rod force and crank angle position. Engineering implementations are carried out on a four-stroke gasoline engine under motored condition. The measurement results are compared with numerical results from a newly developed numerical coupling model system, and it shows that the two agree well. In addition, the piston-assembly friction under different engine speeds and inlet lubricant temperatures are also measured, and analyses indicate that these results are in good correlation with the well-known Stribeck curve. This improved measurement technique provides an accurate and reliable option for the friction evaluation of piston-assembly components in engine designs.