Enhanced engine efficiency through subsystem lubricant viscosity investigations

Abstract

This study initiates a three-year project to investigate the potential benefits in fuel efficiency, engine emissions, lubricant longevity, and engine durability. Two experimental testing platforms were designed and implemented to empirically study the effects of lubricant formulations on the internal combustion engine's frictional losses. A motored cylinder head enables the characterization of valvetrain lubrication regimes and friction contributions. A Kohler KDW-702 engine was also instrumented with pressure and torque measuring instrumentation, in addition to being modified to have two separate lubrication circuits - one to lubrication the valvetrain system, and one for the crankcase system. Using a novel split lubrication strategy, the full engine experimental setup was used to investigate the effect of lubricant viscosity on subsystem friction as well as demonstrate the efficiency gains possible by optimizing lubricant formulations on a subsystem basis. The Kohler KDW-702 test engine was shown to experience significant boundary contact within its valvetrain system, contrasting the predominantly hydrodynamic nature of the crankshaft bearings and piston assembly. A split lubrication configuration addressed this, using a 15W-40 oil in the cylinder head, and a 1OW-30 oil in the crankcase, yielding 6% lower overall friction and 3% higher mechanical efficiency over the stock recommended full 15W-40 lubrication configuration. While significant frictional gains have been demonstrated through the use of a split lubrication system and optimized lubricant viscosity classifications, the project will continue to demonstrate benefits in engine emissions, lubricant degradation, and engine component wear.