Tribometer Investigation of the Frictional Response of Piston Rings when Lubricated with the Separated Phases of Lubricant Contaminated with the Gasoline Engine Biofuel Ethanol and Water

The biofuel ethanol, a viable and cost-effective gasoline substitute, is being blended at increasingly higher concentrations in gasoline, heightening the need to investigate its effects on current automotive engine lubricants in terms of fuel economy and engine durability. The friction at the piston ring/cylinder wall interface with a fully formulated gasoline engine lubricant contaminated with ethanol and water was investigated using a Plint TE77 reciprocating tribometer and reported in a previous paper by the authors. This research takes this one stage further by studying the friction in the same tribometer configuration when lubricated with the separated phases the same contaminated lubricant forms when left undisturbed, as would happen when a vehicle is parked or garaged. The lubricant mixture separated into two distinct phases, an oil phase and a water and ethanol based ‘white sludge’ phase, both phases characterised by FTIR spectroscopy and viscosity. Significant reductions in friction were obtained when the piston ring-cylinder wall interface was lubricated with the separated phases compared to the formulated reference lubricant. When lubricated with the separated oil phase, temperature was shown to be the dominant contributor to the frictional response. When lubricated with the separated sludge phase, ethanol independently contributed to the frictional response whilst the interactions between ethanol and temperature, water and temperature and water and speed were also important.