What does the compression ratio of an engine represent?

The compression ratio of an engine is a crucial measurement that demonstrates the relationship between the total volume of the cylinder when the piston is at the bottom of its stroke (bottom dead center) and the volume remaining in the cylinder when the piston is at the top of its stroke (top dead center). This measurement reflects how much the air-fuel mixture is compressed during the engine cycle before it is ignited.

A higher compression ratio typically allows for greater efficiency and power generation from the engine, as it means that the engine compresses the intake mixture to a smaller volume, leading to a more powerful combustion event. The compression ratio plays a significant role in determining the engine's performance characteristics, fuel efficiency, and the type of fuel it can effectively use.

Understanding the compression ratio helps mechanics and engineers predict engine behavior, including the timing of ignition and the fuel's octane rating necessary to avoid knocking during combustion.