Southwest Research Institute^® (SwRI^®) News

Radioactive tracer measurement techniques for engine tests

Real-time measurement of multiple engine components under test to examine the effects of new fuels, lubricants, and structural materials on engine wear has become possible using a new radioactive tracer technology.

San Antonio — November 20, 1995 — The innovative application of radioactive tracer (RAT) measurement techniques to study multiple engine wear component problems in real time was described to directors and trustees at Southwest Research Institute^® (SwRI^®) 48th Annual Trustees Meeting today. The technology, which evolved from the experience Institute engineers gained investigating wear in nuclear power plant equipment, is carried out under regulated safety conditions.

“Understanding the effects of changing fuels, lubricants, and additive requirements, as well as new materials and designs on the wear of engine parts, is critical if we are to produce engines with longer lives and lower emissions that meet new regulations,” says Martin Treuhaft, manager of Filtration and Fine Particle Technology in the SwRI Fuels and Lubricants Research Division.

“In addition,” Treuhaft adds, “a comparison between RAT and conventional wear measurement techniques show significant cost and time benefits as several components can be simultaneously tested.”

Use of the technology has revealed some unexpected findings. For example, shortly before Operation Desert Storm we were able to demonstrate that replacing air filters in dusty environments too frequently actually increased engine wear. This was a result that few would have believed without the hard data provided by radioactive technology.

Conventional wear measurement techniques require the disassembly of an engine and examination of all worn components. This procedure results in only average accumulated wear measurements. In addition, if the engine is reassembled for further tests, it remains uncertain whether subsequent wear is caused by normal wear processes or by factors introduced during the dismantling and reassembly process.

Using RAT techniques, engine components, such as piston rings and connecting rod bearings, are irradiated to obtain specific, identifiable, radioactive metal isotopes. Each component is then installed and run in an engine over selected time periods. As wear occurs, the isotopes serve as detectable particle tracers as they abrade from the irradiated parts and circulate through the lubrication system.

Radiation from the particles is then measured using a gamma ray spectrometer that is enclosed in a shielded container through which the oil circulates. The level of radioactivity is proportional to the mass of the wear particles for each identified part. Since radioactivity is measured continuously, the wear rate of components can be correlated immediately with changes in engine operating conditions such as load, coolant temperature, lubricant quality, and dust ingestion.

“For example,” says Treuhaft, “excessive lubricant consumption is a significant factor in limiting the life of catalytic converters and a major contributor to particulate emissions in diesel engines. Piston ring and cylinder liner wear can contribute significantly to this consumption. Radioactive tracer technology studies have confirmed that improving the design of these components as well as changing lubricant chemistries can reduce both wear and emissions and produce a better quality engine.” Radioactive tracer technology has also been instrumental in revealing the disproportionate amount of overall engine wear contributed by transient conditions. This discovery may surprise many engine designers and manufacturers, who, without examining the real-time continuous test results of multiple components, would not have believed the effects of varying engine speed and load on wear.

“This is an exciting new tool that allows clients to rapidly and cost-effectively measure what their ideas and products are doing and see the cause and effect relationships necessary for successful product development,” says Treuhaft.

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