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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.

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.

Electrical ac impedance measurements were used for tracking the time dependence of the electrical properties (resistivity and permittivity) for 18 fully formulated engine oils during two types of engine dynamometer tests: high-temperature high-load (HTHL) and postal cycle (PC). The signatures in the time dependence of the electrical resistivity of engine oil at beginning-of life (BOL) and during early service differentiate both oil service classifications and test/driving conditions. The air content in engine oils can be determined quantitatively from the permittivity with a detection limit of 0.2 vol%. The significance of our results and their consequences for on-board monitoring of engine oil through sensing technology based on electrical ac impedance measurements are discussed.

A radiometric method has been developed for the determination of camshaft wear during engine operation. After a radioactive tracer is induced at the tips of one or more cam lobes by the technique of surface layer activation, calibration procedure are performed to determine the amount of radioactive material remaining versus the depth worn. The decrease in γ-ray intensity measured external to the engine is then directly related to cam lobe wear. By incorporating a high-resolution detector and an internal radioactive standard,measurement accuracy better than ±0.2 μm at 95% confidence has been achieved. Without the requirement of engine disassembly, this method has provided unique measurements of break-in wear and wear as a function of operating conditions. Because this approach requires only low levels of radiation, it has significant potential applications in wear control.

The radiotracer technique of surface layer activation was used to study piston ring wear rates in the Detroit Diesel Allison “Series 60” engine. Radioactive 54Mn was induced in the chromium surface of the ring face by bombardment with an α beam from a particle accelerator. Wear of the piston ring surface was determined by measuring the accumulation of radioactive debris in the oil during engine operation and by measuring the radiation intensity of the rings from outside the engine between intervals of engine operation. Information was obtained on the wear rate of the top compression ring during break-in and as a function of engine speed and power output. In addition, piston rings activated around their entire circumference were used to determine wear as a function of angle from the ring gap. The collection efficiency of the oil filtration system, for ring wear debris was also determined by measuring radioactivity in the oil filters.

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.

A radiotracer method has been developed to measure piston ring and cylinder bore wear rates in spark-ignition (SI) engines. The method has sufficient sensitivity to measure ring and bore wear rates in real time during normal operating conditions. This work reports measurements on the rates of break-in and steady-state wear of piston rings and cylinder bores during a variety of engine operating conditions. Results show that piston ring break-in is minimal and that ring wear rates are constant at steady-state engine operation. The key factor affecting ring wear is engine brake mean effective pressure (BMEP). Ring wear behavior is repeatable for a given engine type and between two different engine designs. Cylinder bore wear is dominated by initial break-in, cold-start wear, and changes in operating conditions. Wear of the cylinder bore during steady-state operating conditions is very low when compared to break-in and changes in conditions.

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.