Page "Internal combustion engine" Paragraph 169

The thermodynamic limits assume that the engine is operating under ideal conditions: a frictionless world, ideal gases, perfect insulators, and operation for infinite time.

Real world applications introduce complexities that reduce efficiency.

For example, a real engine runs best at a specific load, termed its power band.

The engine in a car cruising on a highway is usually operating significantly below its ideal load, because it is designed for the higher loads required for rapid acceleration.

In addition, factors such as wind resistance reduce overall system efficiency.

Engine fuel economy is usually measured in the units of miles per gallon ( or fuel consumption in liters per 100 kilometers ) for automobiles.

The volume of hydrocarbon assumes a standard energy content.