The compression ratio is a measure of the difference between the volume of the cylinder when the piston is at its highest point (top dead center) and the volume when the piston is at its lowest point (bottom dead center). It is used to determine the efficiency of an internal combustion engine.
Higher compression ratios typically result in more power and efficiency, as the fuel-air mixture is compressed to a smaller volume before ignition, leading to a more powerful explosion. However, too high of a compression ratio can also cause knocking or pre-ignition, which can damage the engine.
The two main types of compression ratios are static and dynamic. Static compression ratio is the ratio of the cylinder volume at bottom dead center to the volume at top dead center. Dynamic compression ratio takes into account the actual volume of air and fuel in the cylinder during the compression stroke.
Compression ratios can be changed by altering the stroke of the piston, the size of the combustion chamber, or the thickness of the head gasket. Different engine designs have different optimal compression ratios, so changes should be made carefully to avoid engine damage.
The ideal compression ratio for an engine depends on various factors such as the type of fuel used, the design of the engine, and its intended use. Generally, most gasoline engines have compression ratios between 8:1 to 12:1, while diesel engines have higher ratios of 14:1 to 25:1 due to the nature of diesel fuel.