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It has long been understood that the piston assembly of the internal combustion engine accounts for a significant proportion of total engine friction. Modern engines are required to have better fuel economy without sacrificing durability. The pursuit of better fuel economy drives trends like downsizing, turbocharging and direct injection fuelling systems that increase cylinder pressures and create a more arduous operating environment for the piston ring / cylinder bore tribocouple. The power-cylinder lubricant is therefore put under increased stress as modern engine technology continues to evolve. The conventional approach to investigating fundamental power-cylinder tribology employs bench-tests founded on assumptions which allow for simplification of experimental conditions.

A novel ultrasonic viscometer for in-situ applications in engine components is presented. The viscosity measurement is performed by shearing the solid-oil contact interface by means of shear ultrasonic waves. Previous approaches to ultrasonically measure the viscosity suffer from poor accuracy owing to the acoustic miss-match between metal component and lubricant [1]. The method described overcomes this limitation by placing an intermediate matching layer between the metal and lubricant. Results are in excellent agreement with the ones obtained with the conventional viscometers when testing Newtonian fluids. This study also highlights that when complex mixtures are tested the viscosity measurement is frequency dependent. At high ultrasonic frequencies, e.g. 10 MHz, it is possible to isolate the viscosity of the base, while to obtain the viscosity of the mixture it is necessary to choose a lower operative frequency, e.g. 100 kHz, to match the fluid particle relaxation time.

Increasing pressure to deliver vehicle fuel efficiency without compromising engine durability places significant demands on engine lubricants. The antiwear capability of the formulation is extremely important as wear on engine parts can lead to engine inefficiency. The rapidly advancing and diversifying array of engine architectures creates ever more arduous conditions under which lubricant additives must perform. The evolution of engine design brings with it the propensity for a variety of wear mechanisms to occur. This paper reports research conducted to rapidly collect key information from which to begin to conceive the design of better screening technologies. An exploration of wear mechanisms using simple bench-top experiments was conducted using a variety of lubricants. A lab based oil-aging technique was used to attempt to create an oil sample with wear properties mimiking those of real engine drains.