What does engine compression ratio mean?

[VonWalker]

Engine compression ratio refers to the degree to which the engine's air-fuel mixture is compressed, expressed as the ratio of the total cylinder volume before compression to the cylinder volume after compression (i.e., combustion chamber volume). Additional information: 1. The vast majority of automobiles use so-called "reciprocating engines", where a piston in the engine cylinder performs linear reciprocating motion repeatedly in cycles. Therefore, within these continuous working strokes, there is a specific range of motion. 2. For a particular engine cylinder, when the piston reaches its lowest point, this position is called bottom dead center, and the entire cylinder volume including the combustion chamber forms the maximum stroke volume. When the piston moves in the opposite direction and reaches the highest point, this position is called top dead center, resulting in the smallest volume condition during the entire piston stroke. The compression ratio to be calculated is the ratio of this maximum stroke volume to the minimum volume.