What does it mean when an engine is said to have a "high compression ratio"?

A high compression ratio in an engine indicates that the air-fuel mixture is compressed into a smaller space before ignition. This compression leads to more efficient combustion, as it allows the engine to produce more power with each cycle. Essentially, by reducing the volume of the combustion chamber, the engine can achieve a higher temperature and pressure during the combustion process. This increase in thermal efficiency means that a high-compression engine can extract more energy from the same amount of fuel compared to an engine with a lower compression ratio.

While larger displacement can affect power output, it is not a direct indicator of compression ratio. Similarly, the efficiency of mixing air and fuel relates more to the design of intake systems than to the compression ratio itself. Engines with higher compression ratios may also run hotter due to the increased combustion temperatures, which contrasts with the notion of running cooler. Thus, the correct interpretation of a high compression ratio revolves around the enhanced power generation capabilities due to reduced combustion chamber volume.