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Radiometric techniques have been developed and successfully applied to journal bearing studies in a unidirectional bearing test machine. These techniques, which involve the detection of wear debris from a radioactive (113Sn) test bearing, were used to determine bearing load capacity with both Newtonian and non-Newtonian lubricants. Results indicate that the radiometric method can rapidly provide information that correlates with other laboratory and engine test data.

Organic acid degradation products and other anions in engine oil were speciated by capillary electrophoresis (CE) and liquid chromatography-mass spectrometry (LCMS) with electrospray ionization. The sample preparation procedure involved selectively extracting the acids and other water soluble salts into 0.05M aqueous potassium hydroxide. Samples of engine-aged mineral oil and synthetic engine oil contained formic acid, acetic acid, and complex mixtures of fatty acid degradation products. CE analysis of formic acid, acetic acid and selected fatty acids is proposed as a new chemical analysis method for evaluating the condition of engine oil and for studying the effects of high temperature-high load (HTHL) oxidation. Because the overall pattern of CE peaks in the electropherogram changes with oil age or condition, CE-fingerprint (i.e., pattern recognition) techniques may also be useful for evaluating an aged oil's condition or remaining service life.

An engine dynamometer test was developed to simulate the effects of high-temperature, high-load driving conditions on the rate of engine oil degradation. The test engine, a 3.4-L 60° V6, is operated at 3000 r/min and 103 Nm load for 125 h at elevated oil and coolant temperatures and without oil additions. Oil samples are collected at regular intervals and analyzed for chemical and physical properties. Results show that five different chemical and physical properties exhibit regular, predictable changes with operating time. By fitting all data to appropriate functional forms, a very precise fit is obtained (r2 typically > 0.97) for the rate of change in each parameter. When these changes are normalized and corrected for oil consumption, their average can be used to calculate an overall Performance Factor.

A radiotracer method was developed to measure real-time wear rates of piston rings and cylinder bores in spark-ignition engines. Initial work determined baseline wear rates during break-in and steady-state operating conditions. This work examines the effects of lubricant properties on wear rates of the ring/bore interface. Results show that engine oil service classification, the level of antiwear additives, severe engine aging, synthetic formulations, and viscosity classification have little or no impact on wear rates. These results suggest that concerns of wear between the rings and cylinder bore may not be a roadblock to extended oil-change intervals. Engine operation under cold temperatures appears to be a very important factor in ring/bore wear.

The time dependence of the electrical properties for several fully formulated engine oils was tracked during engine dynamometer tests. The pattern for the resistivity indicates the existence of two types of processes (fast ion-depleting and slow ion-releasing) whose existence cannot be inferred through standard engine oil analysis. After these processes have subsided, the change in the resistivity correlates with the change in oil viscosity. We show that the peak value of the resistivity at early test times correlates with oil performance longevity as determined from conventional oil analysis parameters. In addition, the permittivity can provide an early warning of a dangerously low oil level. The significance of the results and their consequences for on-board monitoring of oil life through sensing technology based on electrical ac impedance measurements are discussed.

A radioactive tracer method was used to measure the contribution of engine oil to deposits on exhaust system components and particulates in the exhaust gas of a gasoline engine. The technique involves the use of an oil molecule labeled with radioactive 14C. By measuring the 14C concentration in engine deposits, the fraction of carbon derived from the lubricating oil can be determined. Results show that depending on the location of the deposit, oil contributes from 1 to 8% of the carbon deposited, and is independent of engine operating conditions. Oil contribution to particulate filtered from the exhaust gas ranges from 2 to 30% of the carbon, which increases in proportion to engine speed.

Radiometric wear techniques have been applied to determine the effect of fuel-saving engine oils on journal bearing load capacity. A test machine which applied a unidirectional load to a radioactive test bearing was used to evaluate bearing load capacity. The onset of bearing wear with increasing load provided a direct measurement of fluid-film breakdown, which defined hydrodynamic bearing load capacity. From this, an “effective” lubricant viscosity was calculated by comparing the performance of non-Newtonian lubricants to the performance of Newtonian lubricants. Results show that for the oil formulations tested that employ either a low viscosity or a soluble friction modifier to reduce engine friction, there is a high correlation between high-shear viscosity and hydrodynamic load capacity. The use of an insoluble friction modifier resulted in a higher bearing load capacity than expected based on high-shear viscosity.

Radiometric wear measurement techniques have been applied to determine the effect of journal surface finish on journal bearing load capacity. Bearing load capacity was measured by using a test machine that applies a linearly increasing unidirectional load to a radioactive test bearing. The onset of bearing wear provides a direct measurement of fluid-film breakdown, which is used to define hydrodynamic bearing load capacity. By use of a journal that can be located at two different positions on the shaft, the relative difference in load capacity between two journal surface finishes can be measured without the need to disturb the geometry of the bearing. The effect of journal surface finish on bearing load capacity was thereby quantified. In this study, nodular iron journals were prepared to have test surfaces with different levels of surface roughness.