ABSTRACT
The transfer of power from its source of generation to its final destination where useful work occurs is the subject of much study and engineering development. In the case of internal combustion engines, liquid fuel is combusted by compression ignition (diesel) or spark ignition (gasoline). The gas expansion pressure within the combustion chamber drives a piston, which, in turn, translates reciprocal motion into rotary motion via a connecting rod that is attached to a crankshaft. Once the crankshaft is set in motion, pulleys, chains, clutches, bearings, and gears continue the chain of energy transfer to accomplish the ultimate purpose of the engine, be it transportation, pumping, electricity generation, or the like. At every step of the energy transfer process, solid contacts are set in relative
motion, and they often sustain considerable loads acting both normal and tangential to the direction of motion. Unless the contacts are separated by a lubricating film (solid, liquid, or gas), a tremendous amount of frictional heat builds up in the contact zone that can lead to equipment failure in a relatively short period of time. Therefore, the lubricant is one of the most important components of an energy transfer device. This monograph, in part, is devoted to selected performance attributes
of liquid lubricants, particularly mineral oils and synthetic fluids. To fully describe the design features of modern lubricating oils is beyond the scope of this work. However, some elements need to be discussed to serve as the basis for further discussion. Lubricating oils consist of base oils, which are selected on the basis of viscos-
ity, thermal/oxidative stability, and cost. Chemical additives are also present and provide a number of useful functions. Viscosity modifiers (improvers) are oil-soluble polymers that impart useful rheological characteristics over a wide range of temperatures. Pour point depressants are added to prevent paraffin waxes (present in most refined mineral oils) from impeding oil flow at low temperatures. Dispersants, detergents, anti-wear agents, anti-oxidants, corrosion inhibitors, foam inhibitors, and friction modifiers do what their names imply.
