Friction Reduction Due to Lubrication Oil Changes in a Lean-Burn 4-Stroke Natural Gas Engine: Experimental Results

A project to reduce frictional losses from natural gas engines is currently being carried out by a collaborative team from Waukesha Engine Dresser, Massachusetts Institute of Technology (MIT), Colorado State University (CSU), and ExxonMobil. This project is part of the Advanced Reciprocating Engine System (ARES) program led by the US Department of Energy. Changes in lubrication oil have been identified as a way to potentially help meet the ARES goal of developing a natural gas engine with 50% brake thermal efficiency. Previous papers have discussed the computational tools used to evaluate piston-ring/cylinder friction and described the effects of changing various lubrication oil parameters on engine friction. These computational tools were used to predict the effects of changing lubrication oil of a Waukesha VGF 18-liter engine, and this paper presents the experimental results obtained on the engine test bed. Measured reductions in friction mean effective pressure (FMEP) were observed with lower viscosity lubrication oils. Test oil LEF-H (20W) resulted in a ∼ 1.9% improvement in mechanical efficiency (η_mech) and a ∼ 16.5% reduction in FMEP vs. a commercial reference 40W oil. This improvement is a significant step in reaching the ARES goals.