2014 IR&D Annual Report

Elucidating the Effects of Lubricant Viscosity, Oxidation and Soot Loading on Total and Component Engine Friction, 08-R8300

Principal Investigator
Peter M. Lee

Inclusive Dates: 04/01/12 – 01/15/14

Background — Governmental legislation has increased pressure on vehicle manufacturers to reduce exhaust NOx emissions. One way in which this has been achieved in diesel, and now gasoline engines, is the inclusion of exhaust gas recirculation. This technology results in increased soot levels in the lubricant, adversely affecting wear rates and frictional properties of the lubricant. Vehicle manufacturers also are increasing engine loads in an attempt to improve fuel economy resulting in higher operating temperatures, increasing thermal oxidation of the lubricants. In addition, there is a trend towards reduced lubricant viscosities, causing thinner operating films, resulting in increased component contact, which, in turn, results in higher wear rates. There becomes a point where the friction created by component contact outweighs the advantages of lower viscosity lubricants. At this time this is not fully appreciated and is little understood due to the complexities of measuring engine component friction on bench-top rigs. Only measuring the friction of engine components running in an engine will allow direct comparison between results.

Approach — A single cylinder research engine has had all ancillaries removed, ensuring all friction experienced by the engine is caused by engine components only. The engine has been instrumented so total engine friction can be measured. The valvetrain has the cam wheels instrumented to measure instantaneous friction, and the connecting rod has been instrumented with strain gauges to measure piston assembly friction. Bearing friction is calculated by subtracting piston assembly and valvetrain friction from total engine friction. This gives friction for each engine component. The objectives of this project were:

  • Elucidate the effect of reduced lubricant viscosity, lubricant oxidation and lubricant soot loading on engine component friction (valvetrain, bearing and piston assembly)
  • Validate the results for lubricant viscosity against industry standard tests for fuel economy
  • Elucidate the effect of engine load on engine component friction
  • Install piston assembly friction on a Cummins ISX in the SwRI clean diesel program
  • Generate unique knowledge for SwRI, giving employees more authority when talking with clients
  • Create a new and unique capability at SwRI

Accomplishments — The engine, dynamometer and engine control system has been assembled in the test cell and is operational. Four different viscosity lubricants have been supplied and run in the sequence IVD fuel economy test and results reported. Special instrumentation for the engine has been designed, manufactured and successfully used to measure component friction within the engine. Several client tests have been run using this equipment.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.