R. K. Jensen

Automotive lubricants for the next millennium

During the first decades of the next millennium, automobile manufacturers will strive to achieve, in the USA, another twofold increase in energy efficiency and tenfold reduction in emission levels. On the way to achieving these goals, automobile manufacturers will be improving efficiency and emissions of internal combustion engines, while minimizing customer servicing requirements, as well as introducing new unconventional engine technologies and gradually changing energy sourcing from oil to gas, and possibly to hydrogen. Numerous supporting technologies, such as electronics, computers, sensors, fuels, catalysts, lubricants, etc., will be involved in contributing to engine system improvements. This paper describes expected improvements and changes in lubricant technology and points out the need for development of “breakthrough” technologies which could satisfy the near‐term requirements and eventually in the long term, in combination with novel surface technologies and engine design changes, lead to fill‐for‐life engine lubrication.

Regeneration of Amine in Catalytic Inhibition of Oxidation

Kinetic and mechanistic investigations of decomposition of O-sec-hexadecyl- and O-3-heptyl-4,4′-dioctyldiphenylhydroxylamines showed that at 120 and 140°C these compounds rapidly decompose to yield 4,4′-dioctyldiphenylamine. These results suggest that in the catalytic inhibition of oxidation by aromatic secondary amines or corresponding nitroxide radicals at elevated temperatures the decomposition of O-sec-alkyldiarylhydroxylamines leads to regeneration of the parent aromatic secondary amine.

The Friction Reducing Properties of Molybdenum Dialkyldithiocarbamate Additives: Part II - Durability of Friction Reducing Capability

Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001

Relation between Base Oil Composition and Oxidation Stability at Increased Temperatures

The sources of crude oil have become more uncertain, therefore, the quality of base oils may fluctuate. The authors have been studying the effects of base oil composition changes on oxidative stability. The long range goal is to develop a laboratory procedure to predict changes in Automatic Transmission Fluid performance with variation in base stock composition. In this initial study, the compositions often commercially available base oils, plus ten mixtures made from them, have been characterized by NMR and IR spectroscopy and their high temperature (180 C) oxidation rates determined. The relative oxidation stability, as measured in a glassware oxidation test without catalyst, was found to be most sensitive to the sulfur and aromatic content of the base oils. A correlation between composition parameters and oxidation rate has been derived. Presented at the 30th Annual Meeting in Atlanta, Georgia, May 5–8, 1975

Reduced Phosphorus Concentration Effects on Tribological Performance of Passenger Car Engine Oils

Phosphorus is present in engine oils in the form of the antiwear and antioxidation additive zinc dialkyldithiophosphate (ZDDP). Its effects on wear and friction were studied at different temperatures using a high-frequency reciprocating rig (HFRR). The electrically insulating tribofilm formation was measured using an electrical contact resistance (ECR) technique. The wear and friction performance of a fully formulated fresh oil containing 0.05 wt% phosphorus was compared with the corresponding used oil drained from a vehicle. The results show that the wear performance of fresh oils having phosphorus concentration from 0.02 to 0.1 wt% is very similar. Further reduction of phosphorus concentration below 0.02 wt% leads to high wear. The coefficient of friction increases with increased phosphorus concentration at temperatures above 80°C but decreases with increased phosphorus concentration at temperatures below 80°C. The used oil and the fresh 0 wt% P oil running on the original fresh steel surface exhibit higher wear than when both oils were evaluated on a previously formed film from a fresh oil containing 0.05 wt% phosphorus.

The Influence of Autoxidation on Wear Asymmetry with n-Hexadecane

Autoxidation of n-hexadecane had a profound effect on wear behavior as measured in a four-ball machine. For pure n-hexadecane, the wear of the stationary (continuously loaded) balls was very much greater than the wear of the rotating (cyclically loaded) ball under the test conditions employed. Mild autoxidation at 110-kPa oxygen pressure reversed this relationship. Mild autoxidation at low oxygen pressure gave intermediate results. This wear behavior can be related to differences in wear chemistry and contact kinematics for the apposing surfaces. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in San Diego, California, October 22–24, 1984

Interactions Leading to Formation of Low Friction Films in Systems Containing Molybdenum Dialkyldithiocarbamate and Zinc Dialkyldithiophosphate Additives

The friction reducing capability of an additive system containing molybdenum dialkyldithiocarbamate (Mo(dtc)2) and zinc dialkyldithiophosphate (Zn(dtp)2), which is used in advanced low friction engine oils, is gradually depleted with mileage accumulation due to oil oxidation. In order to understand processes involved in this loss of friction reducing capability and to find a way to improve the retention of this capability, we have investigated chemical changes occurring in the Mo(dtc)2/Zn(dtp)2 additive system during oxidation in base oils of different composition and assessed the effects of these changes on friction reduction. It has been previously determined that under oxidative conditions Mo(dtc)2 and Zn(dtp)2 undergo ligand exchange reactions leading to formation of an equilibrium mixture of Mo and Zn dialkyldithiocarbamate and dialkyldithiophosphate products including molybdenum dialkyldithiophosphate, Mo(dtp)2, and zinc dialkyldithiocarbamate, Zn(dtc)2. All these products are known to be antioxidants which during oxidation react with peroxy radicals or hydroperoxides and at the same time undergo series of oxidative conversions producing secondary antioxidants. In our studies the Zn containing products were found to be stronger antioxidants than the corresponding Mo compounds. They effectively prevent chain oxidation and protect Mo compounds from being consumed. Zn(dtp)2 and its conversion products were found to preferentially react during oxidation with hydroperoxides (in oils containing aromatics) and Zn(dtc)2 with peroxy radicals (in paraffinic oils). Extensive base oil oxidation in the systems inhibited by Mo(dtc)2/Zn(dtp)2 begins only when Zn(dtp)2 is completely consumed. This was found to coincide with a complete loss of friction reducing capability despite the fact that Mo compounds are still present in the system. Evidence is presented that this loss of friction reducing efficiency occurs because the polar base oil oxidation products and polar base oil components interfere with friction reducing process involving Mo(dtc)2 and its ligand exchange products. Based on these results, the retention of friction reducing properties can be improved through the use of additional effective antioxidants which protect Mo(dtc)2 and its ligand exchange products from being consumed and prevent formation of polar oxidation products and also through the use of base oils which do not contain polar components or are not prone to form them upon oxidation.