ANALYSIS OF LUBRICATION OF A PISTON-RING PACKAGE (EFFECT OF OIL STARVATION ON OIL FILM THICKNESS)

Theoretical analysis of mixed lubrication has been carried out for a p iston ring package of an automotive reciprocating engine as a method t o elucidate better specifications of rings for reducing friction loss. The starved inlet boundary conditions have been employed for oil film on each ring based upon experimental results obtained through scannin g laser-induced-fluorescence oil film thickness measurement. With cons ideration of oil starvation, the predicted oil film thickness at compr ession rings was in better agreement with that measured than the forme r prediction under fully flooded inlet conditions. Film thickness at t he Ist compression ring under full load firing conditions was predicte d to be smaller than that during motoring, which also agreed with the experimental results, due to the different inlet conditions assumed fo r the oil film at the 2nd compression and upper rail of the oil ring u nder different operating conditions. The predicted oil film thickness was much smaller than that measured at both rails of the oil ring, whi ch seems to have been caused mainly by limitations of the spatial anal ysis of the LIF measurement. Effects of the change of the oil ring sur face profile due to tilting during sliding, of viscosity variation and of cylinder bore distortion were not negligible, but were not conside red in the analysis.