Milton D. Johnson

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.

Inhibition of Oxidation by ZDTP and Ashless Antioxidants in the Presence of Hydroperoxides at 160°C - Part I

Reactions of zinc dialkyldithiophosphates (ZDTP) in the presence of hydroperoxides have been further investigated using a model n-hexadecane oxidation system at 160°C. Results obtained with selected primary and secondary alkyl ZDTP added alone and in combination with 2,6-di-tert butyl-4-methylphenol suggest that substantial differences exist between the reactions of these two types of ZDTP with regard to both hydroperoxide decomposition and radical trapping. The best overall oxidation control in the presence of excess hydroperoxides has been provided by i-C3ZDTP in combination with a radical trapping inhibitor. Presented at the 40th Annual Meeting in las Vegas, Nevada May 6–9, 1985

Fuel Efficient Engine Oils, Additive Interactions, Boundary Friction, and Wear

Abstract In order to encourage and accelerate development of advanced engine oils which would further contribute to improvement of engine fuel efficiency, Ford developed and made available to the oil industry a new engine test for determination of fuel efficiency of engine oils. This test, called Sequence VIB, was incorporated into the ILS AC GF-3 engine oil standard to be introduced around the year 2000. The main features of this test are increased emphasis on benefits derived under boundary/mixed lubrication conditions and improved retention of fuel efficiency during engine oil use. Friction reducing capabilities under boundary lubrication conditions can be improved through application of effective friction reducing additives, such as molybdenum dialkyldithio-carbamates (MoDTC), which, in combination with zinc dialkyldithiophosphates (ZnDTP) and other antioxidants, must provide good retention of friction reducing capabilities and also adequate antiwear properties. Formulation of such additive systems requires better understanding of various factors affecting performance of MoDTC and their interactions with other additives. From the results of our studies it is clear that ligand exchange reactions between MoDTC and ZnDTP and oxidation and antioxidant reactions involving base oil components, additives, and intermediates derived from them are all important in optimizing the performance and maximizing the benefits derived from these systems. These reactions, although occurring first in the bulk lubricant, also play a very important role in tribochemical conversions in boundary contacts where they are enhanced by more severe conditions. Thus, fundamental understanding of mechanisms and kinetics of these reactions is essential in the process of designing optimized lubrication systems that provide efficient and lasting friction reduction. Along these lines, this paper is intended to review available information, present the most recent data, explain some of the observations, draw some general conclusions, and outline future needs.

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.

ANTIOXIDANT DECAY IN ENGINE OILS DURING LABORATORY TESTS AND LONG DRAIN INTERVAL SERVICE

A new method for the determination of antioxidant capacity in lubricants has been utilized for the analyses of new and used engine oil samples. The results derived from these analyses were used for monitoring the antioxidant decay during laboratory and long drain fleet testing and in various correlation studies. The application of the method provided new insights into the nature of the oxidative deterioration of engine oils as a function of type and initial concentration of antioxidant additives, of type of base oil and of test or engine severity.