Compression ratio

It is the ratio of the total volume of the cylinder when the piston is at bottom dead center to the volume of the combustion chamber when the piston is at top dead center.
The compression ratio of an engine can be shown as.
Compression ratio = Total volume / Clearance volume
In petrol engine, compression ratio is kept as high as 11.5:1 and in diesel engine, compression ratios are as high as 20:1. An increase in the compression ratio results in a higher degree of compression. The combustion will occur at a faster rate.