Resumo

FITTON, J. C.  e  NATES, R. J.. Investigation into the relationship between knock intensity and piston seizure. R&D j. (Matieland, Online) [online]. 1992, vol.8, pp.2-7. ISSN 2309-8988.

This work concerns an investigation into the role of knock on piston seizure in spark-ignition engines. The scope of the research includes a theoretical evaluation of the relationship between knock intensity and ring gap closure, together with the subsequent fatigue and failure of the piston land. An experimental technique is developed to determine the ring gap as a function of knock intensity under operating conditions in a CFR research engine. The results of both the theoretical and experimental study show that knock intensity has a significant effect on ring gap closure. From this, it is evident that knock produces disturbances in the quench zone, resulting in a general increase in the heat flux to the combustion chamber surfaces. The resulting thermal expansion of the ring is sufficient to cause fatigue failure of the piston second land. An exponential reduction in the piston life is predicted when moving from light to heavy knock conditions. This is particularly problematic under high speed knock conditions where the operator would be unaware of any problem until catastrophic failure. This work was performed as a final year BSc (Mech Eng) project at the University of Cape Town.

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