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The oil consumption phenomena during transient engine operating condition is analyzed. The investigation of the oil consumption by means of the real-time oil consumption meter shows that higher intake manifold vacuum during engine-brake condition causes a larger amount of transient oil consumption. The reverse blowby gas flow into the combustion chamber from the crankcase is generated by the high vacuum under engine-brake condition. It is found that this reverse gas flow carries the oil into the chamber from the third land of the piston through the ring end gap of the compression rings. The oil on the piston skirt leaks into the third land through the clearance between the oil ring and the cylinder bore. The weakened bore-to-ring contact pressure by the piston slap motion increases the amount of the leakage oil. New ring sets and pistons are developed based on the results of this study.

A study was conducted to reduce unburned oil fractions in diesel particulate matter (PM) by improving oil consumption. A method utilizing radioisotope 14C was developed to measure the unburned oil fractions separately for the four paths by which oil is consumed: valve stem seals, piston rings, PCV system, turbocharger. The conversion ratio of oil consumption to PM was calculated by comparing the unburned oil emission rates with oil consumption rates, which were obtained by the use of the 35S tracer method. The result in an experimental diesel engine shows the highest conversion ratio for the oil leaking through the valve stem seals. The modifications to the engine were thereby focused on reducing the leakage of the stem seals. This stem seal modification, along with piston ring improvements, reduced oil consumption, resulting in the unburned oil fractions in PM being effectively reduced.

A new method of continuous measurement of engine oil consumption using sulfur as the tracer has been developed. The modified non-dispersive-infrared (NDIR) analyzer with the SO2 absorbent and a permeable plastic type dryer enable to measure very low concentration of SO2 in the exhaust gas. By the use of this method, the engine oil consumption under the transient engine operating condition has been analyzed. The experimental result show that the measured value of the transient oil consumption is larger than the estimated value by the quasisteady method using the experimental data of steady-state operations. The difference between these value is explained by the simple model developed here. This model also show that the total oil consumption under the transient engine operating condition depends mainly on the amount of oil drawn into the combustion chamber by the high vacuum during engine-brake conditions.