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-NO_x 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. Results obtained show that the change of LOC with the test oil is mostly equal to that of LOE under the same engine operating conditions concerning the gas pressure, the temperature of cylinder wall, the viscosity and the rotational speed. The supercharging operation has the effect of reducing the LOC because the LOE decreases as the gas pressure becomes high. The devised analysis method is more useful to predict the rate of LOE for the multi-species component oil and examine the influence of the oil volatility on the LOC.
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