Development and analysis of a fire ring wear model for a piston engine

Ring wear may not be a problem in most current automotive engines, however a small alteration in the ring face geometry can significantly affect the hydrodynamic lubrication characteristics of the ring. This in turn can cause excessive frictional losses and blowby in an engine. As engines become more compact and highly loaded, ring wear is likely to be more severe than in current engines. To be able to assess the effect of ring loading, a piston ring wear model has been developed through the use of ring dynamics analysis with the assumption of a linear relationship between ring wear and the friction work applied on the surface of the ring. It is also assumed that ring wear occurs only in the mixed or boundary lubrication regime, where the hydrodynamic film breaks down. The lubrication regimes are separated by the nominal minimum film thickness, which is defined by the ratio of the minimum oil film thickness to the effective surface roughness of the joint.; Input dynamics to the piston ring wear model were provided by a commercially available ring dynamics analysis program which has been under development for the past five years. Analysis shows that the minimum oil film thickness at a given engine speed tends to be lower just after TDC and BDC, which implies that mixed lubrication occurs between the piston ring and the cylinder wall at these points. This effect appears more prominent at the lower engine speeds than at the higher engine speeds under the same power output. The equation developed for the piston ring wear model is based on the several results of experimental wear efforts. This ring wear analysis clearly shows that the higher the engine speed, the lower the wear rates at the same power output, as is obtained through the experiment. The specific wear rate at steady state drawn from this analysis corresponds to the maximum value of the wear coefficient observed in other experimental studies.; The present analysis was developed and the predictions were compared to data available for a Diesel engine. The model developed in this study can be applied to any piston engine, as long as the specifications of the engine such as the oil viscosity, temperature distributions in the cylinder bore, the ring geometry, the ratio of cylinder bore hardness to ring hardness, and the ring face profile are given as the same. This is the first model of piston ring wear which includes ring dynamics, and is intended to provide a framework for a general model which can include the factors mentioned above. This ring wear model can be used to estimate apriori wear rates for RII or SLA studies.