Oil film thickness distribution between piston ring and cylinder considering non-circular of cylinder bore

In order to investigate the effect of non-circular of cylinder bore on tribological properties of oil film between cylinder and piston ring, a new theory and method to calculate oil film thickness between piston ring and cylinder was presented, considering non-circular of the cylinder bore in firing condition. The deformation of the piston ring was obtained using three moment equations on continuous beam to get the equilibrium of forces on it including gas pressure, ring tension and supporting force from oil film, afterwards, the oil film thickness between piston ring and cylinder was calculated. Results indicated that distribution of the film thickness between piston ring and cylinder along the circumferential direction not only was affected by forces on it, but also had a close relationship with shape and magnitude of cylinder deformation. At top dead moment in suction stroke, the maximum ratios of minimum value, maximum value and mean value of oil film thickness along circumferential direction in four different cylinders reached 1.08, 1.78, 1.37 respectively. Comparing with that between piston ring and ideal round cylinder, mean value of oil film thickness along circumferential direction between piston ring and non-circular cylinder bore was bigger.