The Effect of Friction Modifiers and DI Package on Friction Reduction Potential of Next Generation Engine Oils: Part II Aged Oils

Engine oil plays an important role in improving fuel economy of vehicles by reducing frictional losses in an engine. Our previous investigation explored the friction reduction potential of next generation engine oils by looking into the effects of friction modifiers and dispersant Inhibitor packages when engine oil was fresh. However, engine oil starts aging the moment engine start firing because of high temperature and interactions with combustion gases. Therefore, it is more relevant to investigate friction characteristics of aged oils. In this investigation, oils were aged for 5000 miles in taxi cab application. The friction and wear protection characteristics were evaluated in laboratory bench tests i.e., MiniTraction Machine 2 under rolling/sliding conditions, lubricant film thickness measurements using ElastoHydrodynamic Lubrication (EHL) rig followed by tribo-film analysis by surface sensitive analytical techniques i.e., Auger and Time-of-Flight - Secondary Ion Mass Spectroscopies. Finally, the friction characteristics of aged oils were evaluated using a motored cranktrain rig. It was observed that aged oils took longer to form a protective tribo-film under rolling/sliding conditions and the composition of the film was different that than formed with fresh oils in the sense that tribo-films contained higher concentration of additive elements and phosphates and sulfites. This is possibly related to improved wear protection capability observed with aged oils. Motored cranktrain friction data did not show any degradation with aged oils.