Cylinder liner wear at top ring reversal point: Engine experiment and simulation model

A new technique has been developed to measure the wear and surface texture of the cylinder liner at the top ring reversal point (TRRP) in an internal combustion engine under actual running conditions without the need to disassemble the engine. A wear probe was designed, manufactured and installed in a single cylinder S.I. engine to measure the wear at TRRP over the break-in period. The wear mechanisms were determined from examining the surface texture of the wear probe by using the Scanning Electron Microscope, the optical microscope and the 3-D laser stylus. The probe surface was examined before, during and after the break-in period. The highest rate of wear was found to occur at the beginning of the break-in period, and decreased sharply during the first hour. The wear reached its low steady rate after three and half hours of engine break-in. The primary wear mechanisms were found to be abrasion and plastic deformation.; In addition, the total instantaneous engine frictional torque was measured. The friction and surface roughness, Ra, decreased with time took around 20 hours longer than the wear to reach their steady states. Correlations between the rates of change in wear, surface roughness and engine friction over the break-in period were developed.; A one-dimensional elstohydrodynamic mixed lubrication, friction and wear model was developed. Wear is predicted based on the surface asperity contact pressure. The model can predict the effects of surface roughness, asperity contact, temperature-pressure-viscosity on wear, lubrication and friction of the piston rings and cylinder liner. The cylinder bore wear during the engine break-in was simulated and compared with the experimental results. The predicted cylinder bore wear at TRRP showed a good agreement with the engine test results. The following results are obtained from the model: (a) the minimum oil film thickness, the highest asperity contact friction and the most serious wear on the cylinder liner surface occur at the TRRP in the beginning of the expansion stroke, (b) the oil film thickness decreases and the wear of the cylinder bore and the piston rings increases at higher cylinder wall temperatures, (c) the combined ring friction due to both hydrodynamic and asperity contact is affected by the oil temperature and reaches a minimum level at a certain temperature and (d) the increase in surface roughness causes a drop in oil film thickness and an increase in ring pack friction and liner wear.