What does the compression ratio indicate about an engine?

The compression ratio is a key factor in determining the efficiency of an engine. It is defined as the ratio of the volume of the combustion chamber when the piston is at the bottom of its stroke compared to the volume when the piston is at the top of its stroke. A higher compression ratio generally indicates that the engine can extract more energy from the combustion process, leading to better thermal efficiency. This is because, with a higher compression ratio, the air-fuel mixture is compressed more tightly, allowing for a more complete and efficient combustion event.

Engines with higher compression ratios tend to convert more of the fuel's energy into useful work, making them more efficient overall. This efficiency is why higher compression ratios are often associated with performance-oriented engines and those designed to use premium fuels that can withstand higher pressures without knocking. Understanding the compression ratio is crucial for optimizing engine performance and ensuring that the combustion process operates as effectively as possible.