Assessment of the Properties of Internal Combustion Engine Lubricants Using an Onboard Sensor

Abstract

The physical properties of diesel engine oil were quantified through direct, real-time measurements using an onboard sensor. The sensor measures the lubricant temperature, density, dynamic viscosity, and dielectric constant. Bench-top experiments were conducted to validate the accuracy of sensor outputs against results from ASTM test methods or reference instruments over a specific temperature range. Bench-top experiments were also used to establish correlations between fuel contamination levels and changes in lubricant properties. Measurements were then conducted in a diesel engine using the onboard sensor to quantify changes in the lubricant physical properties with respect to engine operating time.

Through bench-top testing, it was determined that the onboard sensor's viscosity output is accurate to within 6% of results obtained through the ASTM standard method, whereas dielectric constant readings displayed a 7% systematic error with respect to reference values. The oil viscosity was found to decrease by 20% when fuel contamination increased by 10.5% with respect to the baseline value. The dielectric constant showed marginal sensitivity to fuel contamination but significant dependence on the oil additive package. Data measured during engine operation demonstrated a significant, simultaneous increase in viscosity and a decrease in dielectric constant during the first 73 h of testing. The change in the lubricant properties might be attributed to incipient consumption of the additive package and accumulation of oxidation by-products.

KEY WORDS:

• Oil Condition Monitoring
• Diesel Engines

ACKNOWLEDGEMENTS

This material is based upon work for the Center for Advanced Vehicle Design and Simulation (CAViDS). The work was supported by the U.S. Army TACOM Life Cycle Command under contract No. W56HZB-08-C-0236, through a subcontract with Mississippi State University, and was performed for the simulation-based reliability and safety (SIMBRS) Research Program.

The authors are grateful to Peter Thannhauser, laboratory technician, and to undergraduate mechanical engineering students Michael J. Nienhuis and Matthew S. Roobol for their assistance with engine setup and instrumentation.

Review led by Benjamin De Koven