Valvetrain Friction and Wear Performance of Polyalkylene Glycol Engine Oils. Issue 1 (2nd January 2018) - Gangopadhyay, A.
ABSTRACT: The application of polyalkylene glycol (PAG) as a base stock for engine oil formulation has been explored for substantial fuel economy gains over traditional formulations with mineral oils. Various PAG chemistries were explored by varying the feedstock material. All but one formulation have the same additive package. The friction performance of these oils was evaluated in a motored valvetrain rig with current production engine hardware in the temperature range 40–100°C and in the speed range 300–2, 500 rpm. PAG formulations showed up to 48% friction reduction over GF-5 SAE 5W-20 oil depending on temperature, speed, and oil chemistry. The wear protection capability was evaluated using a radiotracer technique on another motored valvetrain rig where only one cam lobe rotated against a bucket tappet. The wear trend of some PAG oils was equal to or better than that of GF-5 SAE 5W-20 oil, whereas others showed high initial wear. The wear rate of the PAG oils was not significantly different from that of GF-5 oil. The bucket tappet surfaces were analyzed using scanning electron microscopy, auger electron spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy to characterize the tribofilm formed and to help explain the friction and wear performance.