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Quick Look Engine Wear Trending Using Radioactive Tracer Technology, 03-9126 Printer Friendly VersionPrincipal Investigators Inclusive Dates: 02/25/99 - 06/23/99 Background - Wear of internal engine components is of major importance in determining performance, exhaust emissions, maintenance requirements, and longevity. Conventional wear testing is time consuming, relatively expensive, and inexact. In this type of testing, components of interest are removed, measured, and reinstalled in preparation for testing. The engine is then run for hundreds of hours, after which it is disassembled for remeasurement, yielding two data points. This process can alter the wear state, compromising further testing. Furthermore, since only two data points are obtained per test segment, it is likely that little is learned about the real wear history of the engine or about specific cause-and-effect relationships. Solving wear problems can become experimentally cumbersome, exasperatingly slow, and unacceptably expensive. SwRI has overcome many difficulties by developing methods for measuring engine wear using radioactive tracer technology (RATT®). These methods measure wear in real time, when historic trending is apparent. RATT has been successfully employed on numerous projects. One protocol developed over the years measures lubricant quality through repetitive series of short tests, during which wear performance of specific lubricants is compared to wear performance using known reference oils. As an experimental expedient, individual test runs are accomplished without filtration. This lack of filtration likely has no adverse affect because 1) each test segment is short enough that the oil is not stressed with respect to breakdown products, 2) wear particles are much smaller than those normally collected by the oil filter, and 3) the oil is drained and the engine flushed following each test. However, when considering longevity and modeling wear over extended periods of time, potential oil degradation and filtration must be considered. For this reason, quick-look funding was sought to conduct experiments combining standard unfiltered tests with longer-term tests using normal filtration. These results would be examined in their own light and with respect to results from previous tests conducted without filtration. This process would also allow SwRI to gauge the effectiveness of its technologies and test protocols with respect to known client needs and interests and to assess the potential for extending its capabilities to include oil degradation and filtration. Approach - The overall objective of this project was to investigate impacts of oil condition and filtration on the measurement of piston ring and rod bearing wear when employing standard radioactive tracer methods of wear measurement. Work centered on conducting a series of interrelated tests designed to experimentally investigate this situation. In particular, sequential tests were conducted to compare the amount of ring and bearing wear measured during three consecutive operating scenarios. The first scenario consisted of repetitive, standard, short-duration tests (6.23 hours) using clean oil without filtration. The second scenario replicated the first scenario, except conditioned oil was used. This oil was obtained by operating the engine for 72 hours with filtration. The third scenario repeated the first scenario, again using clean oil without filtration. The 2.5-liter gasoline test engine was refitted with bulk-activated compression rings and connecting rod bearings and equipped with a radioactive tracer sampling loop. On-line wear was measured, and post-test bottle samples were obtained for each unfiltered test. In addition, the oil filter was post-processed to determine the source and mass of irradiated wear debris collected during the 72-hour oil-conditioning run. Results were analyzed for cumulative wear and wear rate trending during each test and for overall trending of sequential end-of-test, cumulative wear. Accomplishments - The experiments were successful and much was learned. While radiometric analysis of the oil filter showed it collected significant amounts of wear debris, radiotracer wear data showed that filtration had no noticeable affect on wear particle removal until approximately 20 hours into the oil-conditioning test run. This result supports the decision not to include filtration in the shorter, standard test protocol. The radiotracer data also showed periods of wear particle reentrainment, dispersion, and recollection, following engine restarts and idle periods during the oil-stressing test run. Radioactive tracer technology could be used to measure filter performance and engine wear simultaneously, providing a powerful tool for investigating filtration requirements, an often-asked inquiry. Filter involvement during longer term testing must be taken into account in developing test plans and evaluating results. Testing with partially stressed oil, which contained some wear debris, produced less wear than testing with clean oil. This finding was unexpected and initially confusing (further inquiry suggested that the result was not so surprising, as many oil chemistries require time and temperature to enhance their effectiveness). Although based on limited data, the finding could be significant, and verification should be pursued. If the finding is verified, the mechanisms should be determined, and ramifications with respect to oil change intervals, filter involvement, and additive packages should be considered. A similar finding for diesel engines could have even greater significance, since the topics of extended oil drain and, in some cases heavy exhaust gas recirculation are of major interest. Although the conditioning run altered the oil, it did not stress or render it unusable (as noted, there is indication that it was tribologically improved). As such, the impact of testing with significantly stressed oil was not measured and remains a future objective. Engines, Fuels,
Lubricants, and Vehicle Systems Program |
