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It is effective in engine fuel economy to reduce the viscous friction by applying lubricating oil with low viscosity. The lower viscosity such as SAE0W20, however, increase lubricating oil consumption, LOC. In addition, it has become urgent to reduce the LOC because the emission of the sulfide ash, phosphorous and sulfur contents degrades the diesel particulate filter and the de-NOx catalyst, in addition to which the emission of metal oxide contents from oil additives can cause pre-ignition in highly supercharged spark ignition engines. In order to clarify the LOC mechanism of low viscosity oils, the LOC rates were measured with a supercharged diesel engine under various operating conditions when lubricated with SAE30 or SAE10W30 test oil, and the resulting data have been compared with the rates of the evaporation from the oil-film on the cylinder wall, LOE, as predicted by the devised analysis method for multi-species component oils.

In order to improve the performance of a reciprocating engine by reducing friction loss the authors have studied some characteristics of total friction loss of engine, friction of piston assembly and friction of cam / follower. Firstly, the total friction loss is accurately measured by a convenient engine run-out method to examine the change of total friction mean effective pressure with engine speed, load rate and oil temperature in a fired and braked engine. The influence of piston / cylinder assembly exchange from the worn to the unworn on friction is then examined, followed by the difference of friction loss between SAE30 and SAE10W-30 engine oils. Secondly, the cyclic change of piston assembly friction under the firing condition is measured by an improved floating liner method. Also, the friction characteristics of piston rings are investigated by comparing results with the theoretical values predicted in the mixed lubrication regime under the oil starvation condition.