Abstract
A wear measurement technique using radioactive isotopes is enhanced to facilitate the comparison of model-component tribometer tests with an engine bench test in order to investigate the lubricating performance of oils contaminated with fuel and its combustion products.
Wear measurement with radioactive isotopes proved to be the most powerful technique to quantify wear continuously during short-term experiments, when realistic loading conditions are applied. By means of thin layer activation (TLA) surface layers of only a few micrometers are doped with radioactive isotopes in such way that the total activity is below the free handling limit but provides nanoscopic resolution for wear measurement at the same time. The total wear measured by means of radioactive isotopes is compared to optical surface topography measurement and optical emission spectroscopy after the experiment. The wear measurement technique by means of radioactive isotopes opens up the possibility to establish a correlation between component/model tribometer tests and engine bench tests. This is based on the high sensitivity and on the application potential of the technique in both environments. The bench test is performed with a modern 2.0 litre passenger-car engine. The model/component tests are carried out with a SRV® tribometer with piston ring and cylinder liner components in reciprocating movement.
The wearing behaviour of piston rings during running-in and steady state conditions can be investigated in both environments – in the component and in the engine bench test – in-situ and continuously. The analysis of the steady state wear indicates the lubricating performance of the oil and allows for investigation of impacts due to fuels or bio-fuel blends.
Keywords: wear measurement, radioactive isotopes, model tribometer, engine bench test, lubricant dilution,