What does engine compression ratio mean?

[Jones]

It refers to the ratio between the maximum and minimum volume of gas in the cylinder during piston movement. When the piston is at its lowest point, the gas volume in the cylinder is at its maximum (called total cylinder volume). When the piston is at its highest point, the gas volume is at its minimum (called combustion chamber volume). Below are relevant explanations: 1. Stroke form: All follow the four-stroke cycle - intake, compression, power, and exhaust. The intake and power strokes occur when the piston is at bottom dead center, while compression and exhaust occur at top dead center. 2. Mixture volume: If the cylinder volume is 10 when the piston is at bottom dead center, and the compressed mixture volume is 1 at top dead center, then the engine compression ratio is 10:1. Higher compression ratios generally improve fuel efficiency and power output, but excessive ratios can have adverse effects.