Frances E. Lockwood

The Influence of Copper-Containing Additives on Oil Oxidation and Corrosion

The effects of transition metals in either catalyzing or inhibiting oil oxidation in the liquid phase have been extensively reported in the literature. However, little attention has been paid to the surface films formed as by-products of these reactions. In this paper, the authors investigated surface films for the important case of copper-containing additives influencing the oxidation of oil that contacts a steel surface. Copper naphthenate in solution was found to inhibit oil oxidation and to form copper-containing precipitates and deposits on the steel surface. The surface films formed were characterized by X-ray photoelectron spectroscopy, Auger spectroscopy and scanning electron microscopy. The precipitates showed a unique morphology of spherical particles several microns in diameter. A high level of copper naphthenate was found to prevent corrosion of the steel surface.

Measurements of Elasticity in Multigrade Motor Oil at Elevated Pressure

It has been recognized for about 50 years that the addition of polymer to motor oil will result in shear-dependent viscosity at relatively low shear stress. This shear-thinning can be shown to reduce the elastohydrodynamic film thickness and there has been an expectation of a reduced film in hydrodynamic lubrication as well. The expected associated increase in the journal bearing wear, however, has not been observed. The load-supporting benefit of the elastic properties contributed by the polymer has been used as an explanation for the success of the polymer blended oils in this application. The available measurements of elasticity in the form of normal stress differences have been inconclusive regarding their contribution to load support. These measurements have all been at atmospheric pressure, however, and at a very high shear rate. The oil in the load-carrying region of a bearing is at elevated pressure and the elevated pressure may enhance the elasticity. A new experimental technique for the measurement of elasticity in oils at elevated pressure was developed. A Weissenberg rheogoniometer of the parallel plate, torsional flow type has been miniaturized and placed in a 350-MPa pressure vessel. This is essentially a parallel face thrust washer that can support a load unrelated to the usual viscous action. The load capacity due to the liquid elasticity vanishes for low-molecular-weight liquids of the same viscosity. The device has been validated with an NIST non-Newtonian standard reference material and the preliminary measurements on commercial multigrade oils clearly show the effect of elevated pressure. The possibility exists to provide additional load support without a viscous frictional penalty.

Lubricant shear thinning behavior correlated with variation of radius of gyration via molecular dynamics simulations

The shear thinning of a lubricant significantly affects lubrication film generation at high shear rates. The critical shear rate, defined at the onset of shear thinning, marks the transition of lubricant behaviors. It is challenging to capture the entire shear-thinning curve by means of molecular dynamics (MD) simulations owing to the low signal-to-noise ratio or long calculation time at comparatively low shear rates (104-106 s-1), which is likely coincident with the shear rates of interest for lubrication applications. This paper proposes an approach that correlates the shear-thinning phenomenon with the change in the molecular conformation characterized by the radius of gyration of the molecule. Such a correlation should be feasible to capture the major mechanism of shear thinning for small- to moderate-sized non-spherical molecules, which is shear-induced molecular alignment. The idea is demonstrated by analyzing the critical shear rate for squalane (C30H62) and 1-decene trimer (C30H62); it is then implemented to study the behaviors of different molecular weight poly-α-olefin (PAO) structures. Time-temperature-pressure superpositioning (TTPS) is demonstrated and it helps further extend the ranges of the temperature and pressure for shear-thinning behavior analyses. The research leads to a relationship between molecular weight and critical shear rate for PAO structures, and the results are compared with those from the Einstein-Debye equation.

High-Performance Heterocyclic Friction Modifiers for Boundary Lubrication

The demand for increased energy efficiency continuously drives the development of new lubricants. Here we report the design and synthesis of hexahydrotriazine, triazine, and cyclen derivatives as friction modifiers (FMs) for enhanced fuel economy. This series of sulfur- and phosphorus-free oil-soluble heterocyclic ring-based molecules exhibits differing thermal and chemical stability depending on the degree of aromatization and number of linking spacers within the central heterocyclic ring. Thermally stable triazine and cyclen FMs significantly increase friction performance in the boundary lubrication regime. Cyclens in particular reduce friction by up to 70% over a wide temperature range. Detailed experimental investigations of the newly synthesized FMs at elevated temperatures demonstrate their favorable tribological performance under four operating conditions: variable-temperature sliding, linear speed ramping, reciprocating sliding, and rolling–sliding contact. These latest experimental findings suggest the potential of the application of “designer” heterocyclic FMs for reducing frictional loss in motor vehicles.

Modeling and Analysis of Mixed Lubrication in Automotive Valve Train

Environmental regulation and high fuel cost are among the leading driving forces behind the demand of energy efficient vehicles. Together with new engine hardware technologies, engine oil is expected to significantly contribute to improving vehicle fuel economy. New fuel-efficient engine oils are often formulated with advanced additives and low viscosity base oils. Understanding the lubrication performance at key engine components such as the cam and follower in valve train systems becomes critically important to ensure engine durability with the new fuel-efficient low viscosity oils. A full numerical mixed lubrication analysis of the cam and roller follower pair is conducted using the three dimensional line contact mixed elastohydrodynamic lubrication (EHL) model. The results show significant effects of surface roughness, topography, slide-to-roll ratio, and viscosity grade on lubricant film, contact pressure, and subsurface stress.Copyright

Integration of Nanofluids into Commercial Antifreeze Concentrates with ASTM D15 Corrosion Testing

Abstract : Originally five candidates of nano material were chosen for making stable nano dispersions. Nano graphite particles remain a practical choice for nanofluids thermal application after taking divergent performance attributes into full account: significant thermal conductivity increases, minimal viscosity increase, low density for better dispersion stability, and relatively low cost, among others. Three different types of commercial antifreeze coolants were chosen for the integration with graphite nano fluids. Without corrosion inhibitors our nano coolants typically fail both ASTM D15 engine coolant corrosion tests: D1384 and D4340. Yet, heating up and adding in electrolytes are two common ways to destroy a nano particle dispersion. After making adjustments in particle loading, choosing an effective dispersant, and establishing proper dispersant levels, two nano graphite coolants made from two different nano sources passed both engine coolant corrosion tests plus the CID AA-52624A compatibility and storage stability tests. Compared with the base fluid, the nano graphite coolants thermal conductivity has more than a 25% increase at 2 volume percent particle loading, which is a significant enhancement.

Behaviour of Boundary Lubricating Additives on DLC Coatings

The friction properties of a range of boundary lubricating additives in DLC-DLC sliding-rolling, lubricated contact have been investigated. Two types of DLC have been studied, one hydrogenated diamond-like and the other a non-hydrogenated graphitic type. The graphitic-type DLC coating gave initially very low boundary friction with additive-free base oil but after a few minutes of rubbing in thin film conditions this rose to the higher value produced immediately by the diamond-like DLC. With the graphitic-type DLC, ZDDP formed a thin patchy film while MoDTC produced a marked reduction of friction. Lateral force microscopy showed that the latter resulted from the formation of low friction material on the asperity peaks. Some organic friction modifiers preserved the low friction of g-DLC during prolonged rubbing. MoDTC and ZDDP were also effective in reducing friction on diamond-like DLC.© 2007 ASME