How can the compression ratio of an engine be defined?

The compression ratio of an engine is a critical parameter that describes the relationship between the volume of the combustion chamber when the piston is at the bottom of its stroke (BDC) and the volume when the piston is at the top of its stroke (TDC). It is defined as the total volume inside the cylinder (which includes both the swept volume and the clearance volume) divided by the clearance volume.

This means that the acceptable definition considers how much the volume reduces when the piston compresses the air-fuel mixture during the intake and compression stages of the cycle. The correct formula for the compression ratio is expressed as:

Compression ratio = Total volume (swept volume + clearance volume) ÷ Clearance volume

In the context of this question, the definition that reflects this relationship correctly is the one that divides the combined volume (swept volume + clearance volume) by the clearance volume. The other options either misstate this relationship or miscalculate the defined volumes, leading to incorrect representations of how compression ratios are determined in the engine dynamics. Understanding the correct basis for the compression ratio is fundamental for analyzing engine performance and efficiency.