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In order to increase service intervals and reduce the amount and cost of waste disposal, many heavy duty diesel engine operators are investigating the technique of continuously blending small amounts of used lubricating oil into the fuel system for burning while replenishing the sump with fresh oil. The purpose of this study is to investigate the effect that this practice would have on erosion in fuel injectors and, additionally, to establish the level of fuel filtration efficiency needed to prolong injector life. Surface layer activation was used in an 11 liter diesel engine to measure erosion rates during engine operation as concentrations of used oil from 0 - 4% were blended into the fuel. A spot between the spill ports in an injector barrel was irradiated as a critical erosion location and the engine was run near full rated power for 24 hour test increments to establish erosion rates.

As a lubricating oil deteriorates with use, contaminants in the oil build up over time. These contaminants include both chemical constituents such as oil oxidation products and acids due to combustion gases and particulate constituents such as dust and dirt from external sources, wear metal debris, and combustion soot A series of tests were conducted in a test cell to separate these categories of contaminants as much as possible and measure their effect on engine wear using Surface Layer Activation (SLA). A top piston ring, the corresponding cylinder liner and a sliding tappet cam follower were irradiated and the SLA measurements using the direct or marker method were carried out while the engine was running at close to full rated load and speed. In the absence of external contamination, it was found that organic contaminants and wear metals that built up over 200 hours of operation without oil filtration had no effect on wear of the irradiated parts.