Radioactive tracer technology (RATT™) is an important tool for measuring real-time wear in operating engines and other mechanical systems. The use of this technology provides important wear information that is not available by other, more conventional wear measurement methods. The technology has advanced to the point where several components can be interrogated simultaneously, and new methods have extended the method to materials that are normally not amenable to radioactive tracer evaluation. In addition, sensitivity has increased so that the onset of wear can be detected long before practical with non-tracer methods. This improves the ability to measure and determine cause and effect relationships, thus providing a better understanding of wear responses to specific operating conditions and to changes in operating conditions. This paper reviews the radioactive tracer process and recent improvements that have extended its reach in both automotive and non-automotive applications. In the automotive area, RATT is particularly well suited for measuring wear responses of power assembly components to various combustion strategies being developed to meet the more stringent 2007 and 2010 emissions requirements. Many of these strategies include the use of early and/or late fuel injection and heavy EGR, which can have profound effects on the operation of aftertreatment devices and reliability due to engine wear. Liner wear caused by localized fuel impingement can lead to excessive oil consumption, and fuel dilution can cause excessive wear of rings and bearings. Higher boost and cylinder pressures are likely to cause an increase in wear between rings and liners, as well as between rings and piston grooves. Asymmetrical bore wear can result from fuel spray impingement during post-injection. This can promote non-conformal ring adjustment, leading to increased oil consumption, with subsequent damage to diesel particulate filters and catalysts. Fuel on the wall also risks increasing fuel dilution in the engine oil, adversely affecting oil viscosity and lubricity. Heavy EGR can increase soot loading and accelerate aging of the oil. All of these effects are likely to increase the wear rate of other lubricated sliding components in the engine, such as valve trains, camshafts and bearings.
RATT can and has been used to evaluate the impact of EGR operating strategies on engine component wear. The increasing levels of soot in diesel engine oils are raising concern, since high soot, when allowed to agglomerate, may lead to increases in abrasive wear. In addition, soot may absorb some anti-wear additives, reducing the formation of protective layers on component surfaces. Abrasive soot particles may also remove any protective layers that do form. Additives are being evaluated to keep soot dispersed in the oil to limit agglomeration and strategies are also being considered to control soot buildup. RATT has been used extensively to evaluate additive packages in the past and makes an excellent tool for evaluating and developing these strategies today.