Exclusions: Pumping losses result from the flow of intake and exhaust gases. Accessories include coolant and lubricant pump, fans, and other pneumatic systems that may be powered directly by the engine. The losses in these systems depend on parameters other than the traditional concept of lubrication or a lubricant. They comprise 20%−30% of total mechanical losses for accessories for heavy-duty diesels and 30%−50% for pumping loss for gasoline engines, depending on the operating speed and load. While important, these losses are not included in the current focused discussions on mechanical or rubbing friction. With the above exclusions, the three major subsystems of the engine contributing to mechanical friction are thus: (a) piston-ring-liner system, (b) crankshaft and bearings system, and (c) valvetrain system. The exact distribution of the friction among these three groups depends on the particular engine, the component design details, and operating conditions. However, prevalent reported results show that the crankshaft system (main bearing and seals) contributes roughly 50%−100% higher friction than the valvetrain system, and the power cylinder friction approximately equals that from the valvetrain and bearing systems combined. Figure 2 shows a typical partitioning of the mechanical friction in the engine, among the three major component groups [7, 11, 13]. Friction and lubrication in these components groups will next be discussed.