A study of the tribological impact of biodiesel dilution on engine lubricant properties

• Published in: Process safety and environmental protection Vol. 112; pp. 288 - 297
• Main Authors: Hamdan, S.H., Chong, W.W.F., Ng, J.-H., Chong, C.T., Rajoo, S.
• Format: Journal Article
• Language: English
• Published: Rugby Elsevier B.V 01.11.2017; Elsevier Science Ltd
• Subjects: Automobile industry; Automobiles; Automotive engines; Bearing strength; Biodiesel dilution; Biodiesel fuels; Biofuels; Boundary lubrication; Carrying capacity; Coefficient of friction; Cold starts; Compression; Diesel; Diesel engines; Dilution; Engine lubricant; Friction; Fuel economy; Greenhouse effect; Greenhouse gases; Load carrying capacity; Load distribution; Long-term effects; Lubricants; Lubricants & lubrication; Lubrication; Lubrication Stribeck curve; Palm Methyl Ester; Shear rate; Tribology; Tribometer; Tribometer; Friction; Palm Methyl Ester; Biodiesel dilution; Lubrication Stribeck curve; Engine lubricant
• ISSN: 0957-5820; 1744-3598
• DOI: 10.1016/j.psep.2017.05.007

•Biodiesel dilution on lubricant could have adverse effects on engine efficiency.•The tribological impact of biodiesel diluting engine lubricant is studied.•Lubrication Stribeck curve analysis is conducted using a pin-on-disc tribometer.•The acceptable PME dilution level for SAE5W40 is at 17.5-vol%.•The acceptable PME dilution level for SAE10W40 is between 28.0-vol% and 34.5-vol%. The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raised tribological performance concerns among major automobile manufacturers. Biodiesel dilution on engine lubricants could have adverse long-term effects on the engine efficiency, which will reduce the fuel economy, thus, leading to higher greenhouse gas emissions. Therefore, this study investigates the tribological impact of palm methyl ester (PME) diluted in SAE5W40 and SAE10W40 engine lubricants along different lubrication regimes under engine cold start condition. Through lubrication Stribeck curve analysis conducted using a pin-on-disc tribometer, coefficient of friction (CoF) for both engine lubricants showed parabolic maximum behaviour with increasing PME dilution. The CoF reduction beyond these peak values is attributed to the improved friction modifier effect from the now-dominant PME but with reduced load carrying capacity. An effective lubricant should possess both reasonable friction modifier effect and highest load carrying capacity in mitigating boundary friction. Hence, through the study, it could be deduced that the acceptable PME dilution threshold level for SAE5W40 is up to 17.5-vol%, while for SAE10W40 is between 28.0-vol% and 34.5-vol%. PME dilution levels beyond these thresholds could easily cause lubrication film rupture under high load, high shear rate conditions during application along the mixed to boundary lubrication regimes, inducing material wear.