Avan, E., Mills, R., and Dwyer-Joyce, R., "Ultrasonic Imaging of the Piston Ring Oil Film During Operation in a Motored Engine - Towards Oil Film Thickness Measurement," SAE Int. J. Fuels Lubr. 3(2):786-793, 2010, doi:10.4271/2010-01-2179.
The oil film that forms between piston rings and cylinder liners is an essential parameter which influences parasitic loss and emission rates in an internal combustion (IC) engine. Several methods have been used to analyse these thin oil films in the past, however, all these methods have required invasive access to the contact area via a window or a surface mounted sensor in the cylinder wall or liner. This paper introduces a novel approach for the imaging of the piston ring - cylinder contact, non-invasively.A straight beam ultrasonic contact transducer was coupled to the wet-side of the cylinder wall of a motored diesel engine. Ultrasonic waves were propagated through the cylinder wall and reflections from the ring-liner contact were recorded as the piston rings passed over the sensing area. The proportion of an ultrasonic pulse that is reflected from the layer, known as reflection coefficient, varies with the stiffness of the layer and the acoustic properties of the matching materials and lubricant. The transducer has successfully detected the rings and the reflection coefficient has been generated using the recorded reflection from the contact. Future evaluation of the oil film thickness (OFT) at the ring contact has been proposed using various ultrasonic transducers.