Development of the ring zone sampling technique for operating internal combustion engines is described. Results show a standing ring of lubricant in the piston ring zone which is substantially degraded compared to that of the sump lubricant. Recent work shows that the degradation of a formulated lubricant can be followed by multiple sampling points in the ring pack, e.g., complementary anti-oxidant degradation/protection of base oil is demonstrated. ‘Residence times’ for lubricant in the ring zone are defined and their determination discussed. The influence of bore and ring surface finish is emphasised. Extension of the technique to differentiate between different quality of lubricants and the different conditions of first ring and the base of the crown land for a piston is described. The principal areas of detailed knowledge which are not known for piston ring lubrication and tribology are examined.

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