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The authors et al. developed a unique single cylinder diesel engine equipped with a floating liner device for the measurement of piston friction force, aimed at the clarification of the relationship between the multiple fuel injections and the state of piston lubrication. Using this engine, the effects of the post fuel injections on the state of piston lubrication have been checked under this study, according to the variation in the piston friction force. As a result, it is verified that the oil film on the cylinder near the top dead center is diluted immediately with the injected fuel, and that the piston lubrication deteriorates more than anticipated even for the case using the SAE 5W/30 oil, compared with the case where the SAE 0W/20 oil with a lower viscosity is used.

The effect of local lubricant viscosity on the temperature and thickness of oil film on a piston ring in a diesel engine is analyzed by using the Reynolds equation, and unsteady and two-dimensional energy equation with heat generated from viscous dissipation. The oil film viscosity for a multi-grade oil is then estimated by using the local oil film temperature and the local shear rate. Moreover, the heat transfer between ring and liner surfaces is examined. The oil film thickness calculated from this method is lesser than that of the case where the viscosity is based on the liner temperature and the mean shear rate. Maximum values of heat transfer at the ring and liner surfaces are obtained at the vicinity of crank angle where the oil film thickness is at a minimum.