Transient Piston Ring Wear in Automotive Engines Using Fe⁵⁹

A single cylinder engine with a radioactive iron piston ring was used to observe transient wear during break-in, cold start-up, and changes in speed. Small changes in engine speed and load under some conditions produce more wear during a given time interval than steady-state operation at high speeds and loads. Our studies show that measuring transient wear is more difficult than measuring steady-state wear partially because of insufficient counting rates. Errors in measurements due to counting statistics were analyzed. High counting rates will be necessary for reproducible measurements of fast transient wear such as that which occurs with an automatic transmission during acceleration. When premium lubricating oils are used, the piston rings should have specific activities of 3.0 to 30.0 mc/gm of Fe⁵⁹ which require irradiation in reactor fluxes of approximately 7 × 10¹² to 7 × 10¹³ n/cm²/sec. Neutron fluxes of this order have not been available in existing reactors for parts as large as automotive piston rings. However, informative measurements of slow transient wear can be made uniquely with available specific activities.