ABSTRACT

I. INTRODUCTION The main functions [1] of the lubricant used in internal combustion (IC) engines are (1) to create a film between moving surfaces in order to reduce friction and wear, (2) to act as a coolant by heat removal, and (3) to provide suspension of contaminants. However, it should be noted that oil formulations used in IC engines are subject to extremely adverse operating conditions. These include high temperatures (200-300C) and pressures and the potential for contamination by water and unburned fuel through a process known as ‘‘blow-by’’ [2]. For oils to function effectively, it is necessary to introduce a range of additives to the lubricant formulation. Additives are chemical substances that impart new or unique properties or enhance existing properties of the base oil. There are many types of lubricant additive [3-5], each with a different function, and typically about 10 different additives are blended with the base (hydrocarbon) oil to generate a fully formulated lubricant. The specific type and amount of each additive depend on the specific application. With such a complex mixture, questions of synergy, or compatibility, of the various additives can be very important. Correctly formulated, these additives provide optimal engine performance over a wide range of operating conditions. The two main colloidal additives present are the detergent additive for the neutralization of acidic species and the dispersant additive for dispersing carbon and other colloidal particulate contaminants.