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Refinement of Engine In-Cycle Losses of Parasitic and Errant Dynamic Nature

Home  Research Programme  Surface Tribology  Top Compression Ring  Cylinder Liner  Piston Skirt  Experiments   
Surface Measurements
Ultrasound Measurements
Measurement of film thickness
  • Film thickness in the piston-liner conjunctions (rings and skirt) are measured through ultrasonic wave reflection
  • Piezoelectric circular ultrasound crystal elements are bonded to the outer wet surface of a test barrel and properly sealed.
  • The crystal are pulsed and the proportion of the wave reflected from the conjuntional interfaces are recorded by the piezoelectric sensor.
  • The reflected energy within the bandwith of the piezoelectric sensor can be processed to obtain a measure of film thickness


Results shown correspond to 3200 rpm at full throttle

Data for an engine is shown

Lubricant film thickness decreases significantly with combustion loading in expansion stroke around 11 degrees past TDC.



                  Inferring the fluid film regime of lubrication                         






 Code validation against measured film thickness


An ultrasonic piezoelectric sensor measures film thickness between a ring sliding in a halved cylinder liner

The ring is held within a piston ring holder and reciprocates within the stationary liner fitted into a modified Plint TE77 sliding tribometer.

Two different lubricants are used: a) base oil without boundary additives and b) full grade Castrol 10W40

Numerical predictions are made with Elrod modification to the 1D Reynolds equation, taking into account cavitation boundary.

Good agreement is found between experiment and numerical predictions.





Experimental Bench-top for Ring/Liner Tests


A test apparatus is being designed at the University of Sheffield to allow small sections of ring and liner to be tested at different loads and speeds with particular interest at reversal. The rig consists of a modified Plint TE77 mechanical reciprocator potentially allowing a maximum sliding speed of 2.3m/s (at 50Hz). The design of the rig will be extended to enable frictional loading to be recorded alongside film measurements. These tests should help to assess the phenomena occurring during mixed lubrication regime at the stroke ends



Experimental bench-top for ring/liner tests at the University of Sheffield. Left the constructed apparatus, right the original design