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. Coatings, metallurgies, roughness, geometries, loads, speeds and temperatures are all important parameters in simulating tribocouple conditions that underpin fuel economy and durability performance as they exist in the final application. These parameters must be included for meaningful results.
This paper describes a first-of-its kind experimental technique where piston ring / cylinder bore tribology is investigated on a bench-top scale. Cylinder pressure data captured from a firing engine is used to simulate dynamic loading of a piston ring against a section of engine cylinder bore. This operation closely mimics that which is seen around the top dead centre (TDC) in a firing engine; the area where the tribocouple experiences the highest friction and wear. This simulation of engine operation is shown to yield superior friction and wear results, which compare well with data collected from fired engines.