Lubricating oil influence on exhaust hydrocarbon emissions from a gasoline fueled engine

Engine exhaust hydrocarbon emissions have been investigated for different lubricating oils, using gasoline as fuel. Six samples of lubricants have been tested: synthetic SAE 5W30 and SAE 5W40, semi-synthetic SAE 15W40 and SAE 20W50, and mineral SAE 15W40 and SAE 20W50. Experiments were carried out in a production engine mounted on a bench test dynamometer, varying engine load and speed in the range from 1500 to 6000 rev/min. The results demonstrate the influence of lubricant viscosity and base oil on hydrocarbon emissions. The synthetic oils showed the lowest hydrocarbon emission levels, especially in the low engine speed range.

► Increasing oil viscosity reduces unburned hydrocarbons production.
► Viscosity effects on HC emissions were noticed for mineral and synthetic oils.
► Oil base effects can overcome oil viscosity effects on fuel absorption/desorption.
► Base effects on hydrocarbon emissions were verified for low viscosity oils.
► Synthetic oils produced lower HC emissions than semi-synthetic and mineral oils.