The sealing effect of piston rings in reciprocating engines have a major impact on blow-by and lube oil consumption (LOC). The sealing is achieved by the gas forces acting on the top and back side of the rings. In addition, the load in the radial direction is increased by the initial ring tension. Inertia forces arising from the oscillating vertical stroke and shear forces due to the secondary piston movement influence this sealing effect by a reduction in contact pressure.
Numerical simulation of the piston and ring dynamics solves this non-linear problem and predicts the interaction between piston secondary motion, axial ring motion, and 2nd land pressure. This paper describes the modeling of the cylinder kit dynamics of a six-cylinder truck diesel engine for several operating conditions and ring modifications. The influence of boundary conditions and adjustment parameters on piston ring motion and gas penetration was investigated. The original gas flow model for predicting the gas flow through the ring package was extended by an additional orifice at piston top land. As a result, the different gas flow quantities on piston major and minor thrust side were taken into account.
A simulation method is described which predicts lube oil consumption due to evaporation from liner wall and mechanical losses of oil which go past the top ring. Furthermore, the paper reviews the comparison of measured and predicted inter-ring gas pressure, axial ring motion and blow-by, which underline the applicability of the simulation.
The principal findings are that top edge scraping of the first compression ring can be influenced by the second land pressure. This top side sealing of the second ring may also cause a radial collapse and lead to a higher remaining amount of oil. In addition, the magnitude of inter-ring gas pressure is shown to be significantly different between the piston major and minor thrust side. This is undoubtedly due to secondary movement of the piston. It is recommended to address this issue when cylinder kit dynamics are analyzed.